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  1. you realize of course that they do not teach geometry anymore, but (grumpy as I am today from a winter cold) your putting Q.E.D. at the end of your article has made me smile, thanks & be well.

    Comment by David Wilson — 6 Aug 2007 @ 4:41 PM

  2. Back in the 1980′s, when the greenhouse effect first reached prominence as an issue, I was a skeptic. I thought if CO2 is the principal driver of global warming, why did most of the 20th century warming happen before 1940, while most of the CO2 accumulation happened after 1940? I figured if there was anything to anthropogenic global warming (AGW) temperatures would continue to rise over the next few decades and the issue would come to a head in the 2000′s.

    Well they did and it has. Given the results of this natural “experiment” and the fact that many laymen are now interested in this issue I decided to look into the science of AGW to see how much I understood and how many results I could obtain for myself using simper models. In the website given above I present my current understanding of AGW in terms of a model that I have implemented on an Excel spreadsheet and which anyone with some math and technical background could do for themselves.

    I bend over backwards to the skeptics by including the cosmic ray mechanism as a central feature of my model. Interestingly, the inclusion of this mechanism *strengthens* the case *for* AGW.

    The reason is that in the absence of the cosmic ray effect the impact of solar is through total solar irradiance (TSI), and is very small. The data I find has a solar cycle size of 1 watt/meter in TSI. With albedo of 0.3 this comes to a 1*(1/4)*(1-0.3) = 0.18 watts/meter impact on average solar insolation which translates to maybe 0.1 C, depending on what you assume for climate sensitivity.

    With the cosmic ray model, the size of this effect rises to ~0.4 C. It cannot be seen directly because of oceanic damping, but it does call for about ~0.3C of warming (instead of ~0.1 C from pure TSI) in the early 20th century based on Lockwood’s solar activity reconstructions. Since solar activity hasn’t risen since the 1950′s, solar contributes zip to recent warming.

    Between 1900 and 1950 the CO2 forcing was about a quarter of the post-1950 forcing, which is capable of producing ~0.7 C of warming. Yet the temperature rise early in the 20th century was not much smaller than the recent rise. With the cosmic ray effect we have ~0.3 C of solar warming combined with ~0.2 of CO2 warming, which is then offset by human-produced aerosols to yield ~0.3 of waring. Since the 1950′s we have ~0 C of solar warming plus ~0.7 C of CO2 warming combined with aerosols to yield ~0.4 C of actual warming.

    Without the cosmic ray solar effect it is harder to explain why the early 20th century temperature rise was so big compared to the post-fifties warming.

    Svensmark and the cosmic ray skeptics have pretty much nailed the case for AGW, despite their intentions.

    Comment by Mike Alexander — 6 Aug 2007 @ 5:08 PM

  3. Loved this post as I am currently studying math (yes In summer) and you mention Logarithims which I’m currently learning. Math makes more sense when it’s related to actual usage rather then numbers on a dry erase board.

    Comment by Chris S — 6 Aug 2007 @ 5:21 PM

  4. Q.E.D.

    The six step explaination is most clear. Thank you.

    Comment by David B. Benson — 6 Aug 2007 @ 5:46 PM

  5. How significant?

    Arctic sea ice (area) on 7/31/07 was 35% less than on 7/31/1997.

    The North Atlantic is warmer than it was 10 years ago. Therefore, we can reasonably speculate that a warming North Atlantic contributed to the weather patterns that caused flooding in England this summer.

    Does anyone want to argue that global warming in some way mitigated the current flood situation in South-East Asia? Is there a weatherman out there willing to state that the heat content of the oceans had no effect on the monsoon? NO? The only other option is that AGW contributed to the effect. We may not be able to quantify the effect at this time, but AGW added its mite.

    I look at the current warming of the North Pacific, and I expect that heat in the water will cause the Pacific storm tracks to move, and change the weather up and down the West Coast of North America. That is significant.

    It is time for weathermen to STOP saying that they cannot attribute specific weather events to AGW. Weather forecasts are going to fall flat unless they account for global warming. Every honest weather man will start their weather forecast, “Because of global warming. . . . “ Then, the public will pay attention.

    And, Gavin has just reminded us that we have not yet seen the full effects from green house gases already emitted!

    Comment by Aaron Lewis — 6 Aug 2007 @ 5:57 PM

  6. As a physicist I can pretty much follow the science on AGW, and can demonstrate to reasonably open-minded people that it exists and is significant. However, I have very little idea what the effects of AGW on humanity will be beyond the fact that it is an ecological disaster which can kill lots of people in the developing world (excellent reasons to do whatever it takes to get rid of it, in my opinion) and so I have a problem with responding to the argument that we need do nothing because at least as far as the DEVELOPED world is concerned AGW will be at most a nuisance.
    Living in Houston, TX where many people work for oil companies I often hear that “plants/animals are cute, but people come first; no breaking the economy for a few critters”, “ok glaciers are on their way out, but people can always build desalinization plants”, “agriculture may be hurt someplaces but will improve in others” and “no matter what this cannot make or break OUR economy and lives. The rest of the world can go XXXX”. Can sbd give me a few arguments to use on such idiots?

    Comment by Konstantin — 6 Aug 2007 @ 7:33 PM

  7. Aaron Lewis> Does anyone want to argue that global warming in some way mitigated the current flood situation in South-East Asia? Is there a weatherman out there willing to state that the heat content of the oceans had no effect on the monsoon? NO? The only other option is that AGW contributed to the effect.

    I do not follow your logic. I think that you at least need to show that current weather extremes are outside what is expected from historical variation.

    [Response: Actually no. To demonstrate attribution you don't need to show that something is unprecedented, merely that it follows consistently. If you take your request to its logical conclusion, we would have to wait until we find ourselves with 10 deg C warming and 100 metres of sea level rise (each of which has happened before) before we could say anything about what was causing it. - gavin]

    Comment by Steve Reynolds — 6 Aug 2007 @ 7:38 PM

  8. Konstantin, this may help:
    http://initforthegold.blogspot.com/2007/07/first-meter.html

    Comment by Hank Roberts — 6 Aug 2007 @ 8:05 PM

  9. A lot of good information. Numbers that I hadn’t seen before. Thank you. I wondered where the coefficient 5.35 came from and I see you point out in part 4., that a doubling of CO2 causes a radiative forcing of 3.7 watts/meter^2 ( within plus or minus .4 w/m^2), then 3.7=Cxln2 or C=3.7/ln2 =5.35 or nearly so.

    Comment by Lawrence Brown — 6 Aug 2007 @ 8:45 PM

  10. I hate to say this, but the world needs to stop all car and plane transport right NOW, for a one year test run. To see if we can survive without these co2 machines……the UN should declare a global emergency NOW and ask all member nations to stop all vehicular and plane traffic NOW. For a one year period, and then get together and see what the results are. We are in a major major emergency, and most media are worring about Paris Hilton and Becks. Who cares? Barry Bonds and A-Rod, not important. The Planet is in DIRE DIRE straights….

    Comment by danny bee — 6 Aug 2007 @ 9:20 PM

  11. Konstantin (#6) wrote:

    Living in Houston, TX where many people work for oil companies I often hear that “plants/animals are cute, but people come first; no breaking the economy for a few critters”, “ok glaciers are on their way out, but people can always build desalinization plants”, “agriculture may be hurt someplaces but will improve in others” and “no matter what this cannot make or break OUR economy and lives. The rest of the world can go XXXX”. Can sbd give me a few arguments to use on such idiots?

    Well, by the end of this century, over a billion people in Asia are going to be facing severe water-shortages as the result of the disappearance of the glaciers in the Tibetean Plateau. This will destroy much of the agriculture in the region. This should drive up food prices worldwide.

    But closer to home, you will see a permanent dustbowel begin to form in the US Southwest – and another begin to form in the US Southeast. We aren’t supposed to be able to grow wheat in the continental US much beyond 2080. Wheat. Thats under business as usual.

    Of course, we could have Canada grow things for us – except they are already using their farmland to capacity. But maybe they could start farming in all of that thawing permafrost…? It tends to have a problem holding water. Not much reason to think the chemistry is right, either, but I have only started digging into their soil. Additionally, farming counts on a great deal of infrastructure being in place. So do cities.

    And it already appears that ice melt is a fairly nonlinear process. Under business as usual could greatly exceed the IPCC’s estimates. Several meters by the end of the century seems quite possible, given the various feedbacks. Five meters isn’t entirely out of the question – either in terms of the dynamics (e.g., positive feedback between Greenland and the West Antarctic Peninsula) or the paleoclimate record.

    Please see:

    However, Hansen et al (2007) show that the typical ~6ky time scale for paleoclimate ice sheet disintegration reflects the half-width of the shortest of the weak orbital forcings that drive the climate change, not an inherent time scale of ice sheets for disintegration. Indeed, the paleoclimate record contains numerous examples of ice sheets yielding sea level rise of several meters per century, with forcings smaller than that of the BAU scenario. The problem with the paleoclimate ice sheet models is that they do not generally contain the physics of ice streams, effects of surface melt descending through crevasses and lubricating basal flow, or realistic interactions with the ocean.

    Hansen, J.E., 2007: Scientific reticence and sea level rise. Environ. Res. Lett., 2, 024002, doi:10.1088/1748-9326/2/2/024002.
    http://pubs.giss.nasa.gov/abstracts/2007/Hansen.html

    And it should be remembered that approximately half of the world’s population lives within 100 km of the coasts. According to the USGS, five meters would submerge 3.2 million kilometers of land, displacing more than half a billion people.

    Please see:

    Modeling Sea-Level Rise Effects on Population using Global Elevation and Land-Cover Data
    E. Lynn Usery (2007)
    http://cegis.usgs.gov/pdf/aag-2007.pdf

    Personally, in economic terms and under business as usual, I believe we could see the beginnings of an economic crisis in this century which will dwarf the Great Depression both in terms of its severity and duration.

    Comment by Timothy Chase — 6 Aug 2007 @ 9:32 PM

  12. Re # 6 Konstantin, here is some more ammunition for you:

    Ecosystem Services provide by Mother Earth include:
    1. Provisioning, including food, water, fuel, and fiber.
    2. Regulating, such as the prevention of soil erosion and flooding.
    3. Cultural, including recreation, spiritual values, and a “sense of place.”
    4. Basic support, including soil formation, nutrient cycling, and oxygen from photosynthesis.

    A few peer-reviewed scientific reports, and summaries of reports, that explain and quantify these services:

    Schröter, D. et al (2005) Ecosystem Service Supply and Vulnerability to Global Change in Europe. Science 25 November 2005, Vol. 310. no. 5752, pp. 1333 – 1337

    Worm, B. et al (2006) Impacts of Biodiversity Loss on Ocean Ecosystem Services. Science 3 November 2006, Vol. 314. no. 5800, pp. 787 – 790

    Stokstad, E. (2005) Taking the Pulse of Earth’s Life-Support Systems
    Science 1 April 2005, Vol. 308. no. 5718, pp. 41 – 43
    Note: This article is an overview of the “Millennium Ecosystem Assessment Synthesis Report,” http://www.maweb.org

    Balvanera, P. et al (2001) Conserving Biodiversity and Ecosystem Services. Science 1 June 2007, Vol. 316. no. 5829, p. 1285

    Kareiva, P. et al (2007)Domesticated Nature: Shaping Landscapes and Ecosystems for Human Welfare. Science 29 June 2007, Vol. 316. no. 5833, pp. 1866 – 1869

    Comment by Chuck Booth — 6 Aug 2007 @ 10:35 PM

  13. Re: 6: Konstantin, I’ve found it effective to point out that, with just another (roughly) 1.5 deg F increase in global ave. temp. (GAT), we will be entering a global climate that the human ecosystem has never seen before. Now note that the most recent IPCC results (Fourth Assessment Report) indicate, with high confidence, a 21st-century temp increase of 3.5-8 deg F. My reading of the paleoclimate data suggests that the last time GAT was 3.5 deg F warmer was roughly 4 million years ago (whereas modern humans came on the scene roughly 150,000 years ago).

    These are knobs on the master control panel that we really don’t want to be twiddling. The full spectrum of the consequences that temp. increases like these – on the timescale of a century – will effect is simply impossible to anticipate. I think that an effective point to make to people is that, from a risk management standpoint, we simply cannot risk the twiddling (“Dad, what does this one do?”). Reading the IPCC working group 3 report one does find some “winners” in the short term, but by century’s end it’s pretty much all bad for human civilization – with strong potential for catastrophically bad.

    Comment by robert davies — 6 Aug 2007 @ 10:55 PM

  14. Re: comment 10 by Danny bee
    It’s often hard to tell if a poster has tongue in cheek, but I’ll assume not in this case.
    Eliminating car & plane transport immediately would be an economic disaster. Over the next few decades shifting much of our road & air traffic to electric rail would be relatively easy. Of course the CO2 emission reductions would be minor unless the electricity is generated by non-fossil (probably nuclear) means.

    Comment by Jim Baerg — 6 Aug 2007 @ 11:43 PM

  15. Another quiet hurricane season this year, huh? And yet “we will see a permanent dust bowl begin to form in the US Southwest – and another begin to form in the US Southeast”

    Pardon me if I don’t trust your rain forecasting.

    The problem you should all be worried about is that the international housing bubble, being substantially more oppressive that this summer’s temperatures, is going to preempt your AGW-derived economic depression by 75 years and steal all of your thunder. Pun intended.

    Comment by Ed Barkley — 7 Aug 2007 @ 12:51 AM

  16. Chaps and ladies,

    Here’s a funny discovered on forum-land. Version 2.0 no less (July 24, 2007). I have a strong suspicion this is Moncktonite bull and requires debunking before the clown brigade start quoting it.

    Gerhard Gerlich, Ralf D. Tscheuschner. Falsification of the atmospheric CO2 greenhouse effects within the frame of physics.

    http://xxx.lanl.gov/PS_cache/arxiv/pdf/0707/0707.1161v2.pdf

    Abstract

    The atmospheric greenhouse effect, an idea that authors trace back to the traditional works of Fourier 1824, Tyndall 1861, and Arrhenius 1896, and which is still supported in global climatology, essentially describes a fictitious mechanism, in which a planetary atmosphere acts as a heat pump driven by an environment that is radiatively interacting with but radiatively equilibrated to the atmospheric system. According to the second law of thermodynamics such a planetary machine can never exist. Nevertheless, in almost all texts of global climatology and in a widespread secondary literature it is taken for granted that such mechanism is real and stands on a firm scientific foundation. In this paper the popular conjecture is analyzed and the underlying physical principles are clarified. By showing that (a) there are no common physical laws between the warming phenomenon in glass houses and the fictitious atmospheric greenhouse effects, (b) there are no calculations to determine an average surface temperature of a planet, (c) the frequently mentioned difference of 33 C is a meaningless number calculated wrongly, (d) the formulas of cavity radiation are used inappropriately, (e) the assumption of a radiative balance is unphysical, (f) thermal conductivity and friction must not be set to zero, the atmospheric greenhouse conjecture is falsified

    End of Abstract

    Comment by Mike Donald — 7 Aug 2007 @ 2:39 AM

  17. I think you lost the readers at step 1! what is sigmaT^4 ?? how is it related to 15C.

    The magical parameters 1-a and S/4 appear from nowhere? what are they?

    [Response: Sorry. I did assume a little knowledge so this isn't the post for absolute beginners. sigmaT^4 is the upward blackbody radiation (based on stefan-boltzmann) at the surface, 'a' is the albedo (reflectivity), so (1-a) is the fraction of incident solar radiation that is absorbed by the planet. And S is the solar constant (1366 W/m2). The factor 1/4 comes from the ratio of the area of the disk to the total surface area of the planet (which takes into account the Earth spherical shape and the difference between day and night). - gavin]

    Comment by John Carter — 7 Aug 2007 @ 3:37 AM

  18. 6.

    Konstantin

    Read ‘Six Degrees’ by Mark Lynas. A good summary of the latest research on temperature change and the impact on human beings.

    James Lovelock ‘The Revenge of Gaia’ will give you a more extreme view. But Peter Ward’s work on mass extinction (especially the Permian Extinction), see his recent article in Scientific American, is even more extreme still. If we get a giant methane bubble due to permafrost melt, then we die.

    Tim Flannery ‘The Weather Makers’ also has a good intro to the impact of temperature changes.

    The idea that the US will be OK if half of the species on this planet dies is a pretty specious one, if you think about it. When you don’t know which species. The honey bee, maybe?

    Then there is the pine bark beetle, which is destroying the forests of British Columbia. And now, due to the warmer winters, it has hopped the Rockies into Alberta.

    And of course there is West Nile Virus, which is moving north with the warmer weather. Close Central Park, anyone?

    You might mention drought in California (Australia is having the worst drought ever recorded, since the white man arrived, and is considering shutting down agriculture in the Murray-Darling system, which is 90% below its normal water level), or the Dust Bowl conditions in the Great Plains in the 1930s (another 5 year drought), or the collapse of water flow into the Colorado River, or category 6 Hurricanes (Katrina was a 4).

    Massive uncontrollable forest fires might be another consequence in places like Colorado. Greece has lost something like 40% of its forest cover this summer.

    Turning to James Hansen’s latest pieces (the technical piece, and the non technical piece in New Scientist) 40% or more of Florida could be under water by 2100, if Hansen is right about glacial melt (which the IPCC explicitly excluded from its forecast).

    Comment by Valuethinker — 7 Aug 2007 @ 5:16 AM

  19. Gavin, your six steps would mean nothing to the vast majority of students I taught over 15 years at the community college level. Way too much math for them!

    I taught Earth Science, a survey course at the freshman level which included the basics of Geology, Meteorology, Oceanography and Astronomy. Yea, I know – a brief brush approach. I picked out of each major topic those subtopics which would mean most to my students, most of whom would never ever see another science course.
    And gobal climate change was a major topic.

    But these students often had not even an algebra background. So I was forced to teach “Physics for Poets” when necessary to explain physical phenomena and concepts. An interesting assignment, for sure.

    These same students, incidentally, read around the tenth grade level. I often had to explain specific words and phrases from the textbook, and the meaning of a long paragraph was often beyond them.

    We need your explanations in those terms to talk to virtually anyone chosen randomly from the public: short words, no math.

    [Response: One thing I've found over the years of dealing directly and indirectly with high school students is that the direct scientist-student route is not very productive (very different assumptions about what an explanation entails!). However, the scientist-teacher then teacher-student route is much more so. Teachers get the scientific points much faster and are also in a much better position (and have more patience) to lead the students to understanding. Therefore, maybe we could help each other out here. Since you presumably understand the points made above (!), perhaps you'd care to translate it down another level - If so, I'll post that up as well and we can see if it works better. - gavin]

    Comment by Bob Bergen — 7 Aug 2007 @ 5:47 AM

  20. Re 15

    sigma*T^4 is the amount of (infrared) energy radiated from 1sqm Area earth surface according to Boltzmann´s law
    http://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law
    sigma is the boltzmann constant; T is absolute temperature in K, the surface temperature (in °C) has to be converted to K (Kelvin – add 273.15K)

    a is the albedo (reflectivity for sunlight) of the earth, it is roughly 0.3 without unit
    http://en.wikipedia.org/wiki/Albedo
    S is the “solar constant”, the amount of solar energy into 1sqm (90° incidence angle) before it enters earths atmosphere, it is roughly 1366W
    http://en.wikipedia.org/wiki/Solar_constant#Solar_constant
    it has to be divided by 4 to account for the area ratio: crossection of a sphere / surface area of a sphere
    (the incident sunlight on earth surface is proportional to the crosssectional area, but the radiated energy is proportional to the surface area)

    Comment by Andree Henkel — 7 Aug 2007 @ 6:04 AM

  21. Thanks for another great post — I really appreciate the efforts you make to make the science behind global warming understandable by the average person. This is a still a bit technical for complete lay people, but generally excellent work.

    Kevin
    http://www.21st-century-citizen.com

    Comment by Kevin — 7 Aug 2007 @ 6:18 AM

  22. Re: 6: Konstantin

    My favourite places on Earth are coral reefs. These ecosystems are among the most diverse on Earth. They directly support large human populations, and indirectly, through tourism, fisheries and medicinal derivatives, support many more.

    Coral reefs are under extreme threat from climate change. Tropical corals are particularly at risk from bleaching, due to higher than average sea temperature, and from calcium carbonate skeleton dissolution as a result of lowering sea pH. It is estimated that up to 50% of coral may be killed by 2030 under present trends.

    See the Australian Great Barrier Reef Marine Park Authorities web site for more info:

    http://www.gbrmpa.gov.au/corp_site/info_services/science/climate_change/climate_change_and_the_great_barrier_reef

    Cold water corals are also under threat, although much less is known about these very recently discovered ecosystems. Check out Lopelia.org

    http://www.lophelia.org/conservation/threats_cc.htm

    Hope that helps.

    Comment by ChrisC — 7 Aug 2007 @ 6:37 AM

  23. [[I hate to say this, but the world needs to stop all car and plane transport right NOW, for a one year test run. To see if we can survive without these co2 machines……]]

    A recipe for instant worldwide recession, not to mention starvation. Food moves on trains, trucks and ships, you know.

    Are you, by any chance, an agent provocateur working for the denialists?

    Comment by Barton Paul Levenson — 7 Aug 2007 @ 6:50 AM

  24. [[I think you lost the readers at step 1! what is sigmaT^4 ?? how is it related to 15C.

    The magical parameters 1-a and S/4 appear from nowhere? what are they?]]

    The “Stefan-Boltzman law” says that a perfect radiator known as a black body emits a flux of so many watts per square meter, depending on the fourth power of the object’s temperature:

    I = σ T4 (1)

    Here, σ is the Stefan-Boltzmann constant, equivalent to about 5.6704 x 10-8 W K-4 m-2 and T is the temperature in °K., I comes out in watts per square meter. For example, Earth’s surface, at a mean global annual temperature of 288° K., radiates 390 watts per square meter. (Or it would if it were a blackbody. Actually, for most objects you have to sandwich in a factor ε called the “emissivity” into the equation above, ε ranging from 0 to 1, and it’s about 0.95 for Earth’s surface.

    The average Solar energy flux falling on the Earth’s surface is

    F = (S / 4) (1 – A)

    Here S is the “Solar constant,” the average flux intercepted by one square meter of space perpendicular to the sun at Earth’s distance from the sun. It has an a canonical value of 1,367.6 watts per square meter. A is the Earth’s “bolometric Bond albedo,” the fraction of solar energy reflected away by the Earth’s surface and atmosphere (mostly by clouds). A for Earth is 0.306 according to NASA. The factor 1/4 arises because Earth intercepts Solar energy on its cross-sectional area — π R2 — but has a spherical surface area — 4 π R2. Or in other words, half the Earth is in darkness and most of it slants away from the Sun.

    Plugging S = 1367.6 and A = 0.306 into the equation above, we find that F is about 237 watts per square meter for the Earth, corresponding to an “equilibrium temperature” (or “emission temperature,” or “effective temperature”) of 254° K. Most formulations use a slightly different S and A and get 255° K. This is actually the temperature you would measure if you tried to calculate Earth’s temperature from a distance. The difference between the 255° K. emission temperature and the 288° K. surface temperature, 33° K., is a measure of the strength of Earth’s greenhouse effect.

    Comment by Barton Paul Levenson — 7 Aug 2007 @ 7:03 AM

  25. Danny Bee could also help by turning off his computer.

    Comment by B Buckner — 7 Aug 2007 @ 7:12 AM

  26. To 15)

    T and sigma are standard nomenclature used in physics to discuss “black body radiation”, i.e. the thermal radiation emitted by a body at temperature T.

    sigma is the Stefan-Boltzmann constant (see e.g. http://en.wikipedia.org/wiki/Stefan-Boltzmann_constant)

    However, a and S still require some more knowing person’s explanation…

    Comment by Gunnar Moller — 7 Aug 2007 @ 7:35 AM

  27. Bob Bergen is right in #19. Once you get the points clear, rewrite in simpler language.

    Simpler than the way a good writer about science can write for smart grade schoolers — write even more simply and clearly for people who may have once been curious but are older and by now tired and barely _care_ about knowing how the world works.

    Writing for smart children is easier than writing for people buried in the everyday noise. Their purchasing power and votes are being trolled for by PR and advertisers every minute. They’re hunkered down and not listening.

    Comment by Hank Roberts — 7 Aug 2007 @ 9:08 AM

  28. I had the cart before the horse in my earlier post #9. The Coefficient 5.35 in the formula RF=5.35ln(CO2/CO2-orig) comes from basic physical principles based on radiation transfer calculations using complex models, as the note in table 6.2 so clearly shows.
    What I did amounts working backwards from the data.

    Comment by Lawrence Brown — 7 Aug 2007 @ 9:09 AM

  29. Could you rewrite 4 to leave out models? That point jumps right into models, and the conclusion relies on it.

    [Response: The conclusion relies on the concept of 'radiative forcing', it doesn't rely on any GCM modelling. The linked post is the simplest explanation of the greenhouse effect that you can write down mathematically, and that is definitely not a GCM. The fundamental point is that if you put more energy into a system, then it will warm up. -gavin]

    Comment by DaveS — 7 Aug 2007 @ 9:46 AM

  30. In the article you write:

    “The climate sensitivity classically defined is the response of global mean temperature to a forcing once all the ‘fast feedbacks’ have occurred (atmospheric temperatures, clouds, water vapour, winds, snow, sea ice etc.), but before any of the ‘slow’ feedbacks have kicked in (ice sheets, vegetation, carbon cycle etc.).”

    You go on to say:

    “the last glacial period is a good example of a large forcing (~7 W/m^2 from ice sheets, greenhouse gases, dust and vegetation) giving a large temperature response (~5 ºC) and implying a sensitivity of about 3ºC (with substantial error bars).”

    This deduced 3 C sensitivity then does not just come from the ‘fast feedbacks’ but includes the ‘slow’ (ice sheet and other ) feedbacks as well ? So it is not the ‘classically defined’ sensitivity ?

    Hansen et al. recently (Climate Change and Trace Gases, Proc. Roy. Soc. A, 2007) argues that that an appropriate sensitivity might be twice the currently accepted value of 3/4 C/(W/m^2) once the ‘slow’ effects are put in. Would you care to comment on that estimate ?

    sidd

    [Response: The ice age calculations are taking the ice sheets etc. as fixed boundary conditions that impart a forcing of their own. Therefore we are only considering the fast feedbacks (i.e. ice sheets are not being seen as a feedback). The 'slow feedback' sensitivity is likely to be higher (since carbon cycle, methane and ice sheet feedbacks are very likely positive), however, estimating that from paleo is tricky since we are moving into a new regime which hasn't ever happened before. In particular, the sensitivity of the Laurentide ice sheet to warming (which you can estimate from paleo) is not likely to be the same as for Greenland. I would therefore be a little wary of giving that a number - it's an interesting point though, and I might explore that in a future post. - gavin]

    Comment by sidd — 7 Aug 2007 @ 10:22 AM

  31. Quoting today’s New York Times, in an article by Reuter’s:

    “The world experienced a series of record-breaking weather events in early 2007, from flooding in Asia to heatwaves in Europe and snowfall in South Africa, the United Nations weather agency said on Tuesday.

    “The World Meteorological Organization (WMO) said global land surface temperatures in January and April were likely the warmest since records began in 1880, at more than 1 degree Celsius higher than average for those months.

    “There have also been severe monsoon floods across South Asia, abnormally heavy rains in northern Europe, China, Sudan, Mozambique and Uruguay, extreme heatwaves in southeastern Europe and Russia, and unusual snowfall in South Africa and South America this year, the WMO said.”

    We’ve spent much of the last year debating the significance of anecdotal evidence. To me, that evidence represents a trend when year-by-year weather fails to swing back toward the previous norm.

    We have begun to see indisputable signs of this. In the U.S. we had, in some places, a cold, dry spring, and there was much ruckus made by those who see weather as ‘constantly changing’ and ‘beyond the influence of man.’ Yet, when we look around the world, we are seeing things that have not been previously observed. Weather volatility, massive shifting of wet/dry regions and seasons, severe events in areas previously untouched by them.

    The world is warming – is there any room left to dispute that? The warming is causing mega-changes in climate and weather patterns – can this, either, be disputed?

    So, we don’t know, where, when, how much and so forth. We don’t know a lot about a lot of things, yet we study them and report the results and subject them to further scrutiny, and we build a body of knowledge.

    Is climate any different than these other areas of human exploration? No, in the sense that this is how knowledge is accumulated. Yes, in the sense that no matter who or what causes these changes, they will affect the entire planet without sympathy. No buying our way out of these effects.

    And yet, don’t we already see that it is the world’s poorest who will be most cataclysmically affected? Those with the least means tend to live in the low lying coastal regions which are most prone to flooding. It occurs to me that these people will be displaced before they are flooded out: conditions will simply become unbearable. Too hot, too humid, too much disease. A human catastrophe is certainly upon us, and in the end the wealth of nations will be severely punished.

    Where will all the dispossessed go?

    Comment by Walt Bennett — 7 Aug 2007 @ 10:37 AM

  32. Re #23 where Barton wrote:

    [[I hate to say this, but the world needs to stop all car and plane transport right NOW, for a one year test run. To see if we can survive without these co2 machines……]]

    A recipe for instant worldwide recession, not to mention starvation. Food moves on trains, trucks and ships, you know.

    Yes but food doesn’t grow in deserts, or survive under flood water and that is what global warming is bringing.

    Google for ‘Forest Fires’ and see how globally they are on the increase, and they are the first step towards desertification.

    Google for ‘Floods’ and see how they are spraeding around the world. Australia, the US, Asia and Britain are all suffering. And that will cause food shortages there.

    As the environmental effects of global warming increase, the disruption to the economy will be far worse than that caused by banning the use of unnecessary transport.

    Comment by Alastair McDonald — 7 Aug 2007 @ 10:43 AM

  33. Konstantin, this will definitely help:
    download from:
    http://www.sciam.com/article.cfm?articleID=00037A5D-
    A938-150E-A93883414B7F0000&sc=I100322
    from the October 2006 issue of Scientific American
    Article: “Impact from the Deep”
    “Strangling heat and gases emanating from the earth and
    sea, not asteroids, most likely caused several ancient mass
    extinctions. Could the same killer-greenhouse conditions
    build once again? ”
    By Peter D. Ward
    The last paragraph of the article says:
    “The so-called thermal extinction at the end of the
    Paleocene began when atmospheric CO2 was just under
    1,000 parts per million (ppm). At the end of the Triassic,
    CO2 was just above 1,000 ppm. Today with CO2 around
    385 ppm, it seems we are still safe. But with atmospheric
    carbon climbing at an annual rate of 2 ppm and expected to
    accelerate to 3 ppm, levels could approach 900 ppm by the
    end of the next century, and conditions that bring about the
    beginnings of ocean anoxia may be in place. How soon
    after that could there be a new greenhouse extinction? That
    is something our society should never find out.”
    The hydrogen sulfide will finally put an end to people who think
    global warming isn’t a problem.

    Comment by Edward Greisch — 7 Aug 2007 @ 10:44 AM

  34. Pondering how everything might play out, one deep concern I have is the relationship between Global Warming and Global Dimming, or the fact that our air pollution blocks a significant amount of solar energy from reaching the surface. This decreases the effects of the GHGs that we’ve already contributed to the atmosphere. So what is likely to happen if/when we have an economic meltdown and a significant portion of global industry grinds to a halt? Seems to me this should lead to rapidly rising temps, and who knows what else? Of course I’m referring to the study of post-911 temp increases from the airline shutdown. Do that worldwide and it seems to me that we’d be in big trouble in weeks or months, not 100 years.

    Please tell me I’m wrong…

    Comment by David York — 7 Aug 2007 @ 11:06 AM

  35. According to the Wikipedia source, the value for earth’s albedo is 0,3 only because clouds are taking into account. The albedo is about a third lower without the clouds (earth’s surface = 70% water).

    Is it allowed to use part of the atmosphere in this kind of calculations?

    Thanks.

    Comment by Jan Janssens — 7 Aug 2007 @ 11:09 AM

  36. I don’t want to hijack the thread, but the cover page of the Newsweek article on oil, coal, gas and transportation industry funding of deniers and the responses to it are amusing and indicative of what is going on politically and why. Sorry if someone has already mentioned it:

    Newsweek front page article:
    http://www.msnbc.msn.com/id/20122975/site/newsweek/page/0/

    Response from a denier with utterly no scientific proof whatsoever:

    http://epw.senate.gov/public/index.cfm?FuseAction=Minority.Blogs&ContentRecord_id=38d98c0a-802a-23ad-48ac-d9f7facb61a7

    Comment by Richard Ordway — 7 Aug 2007 @ 11:50 AM

  37. # Konstantin Says:
    6 August 2007 at 7:33 PM

    As a physicist I can pretty much follow the science on AGW, and can demonstrate to reasonably open-minded people that it exists and is significant. However, I have very little idea what the effects of AGW on humanity will be beyond the fact that it is an ecological disaster which can kill lots of people in the developing world (excellent reasons to do whatever it takes to get rid of it, in my opinion) and so I have a problem with responding to the argument that we need do nothing because at least as far as the DEVELOPED world is concerned AGW will be at most a nuisance.
    Living in Houston, TX where many people work for oil companies I often hear that “plants/animals are cute, but people come first; no breaking the economy for a few critters”, “ok glaciers are on their way out, but people can always build desalinization plants”, “agriculture may be hurt someplaces but will improve in others” and “no matter what this cannot make or break OUR economy and lives. The rest of the world can go XXXX”. Can sbd give me a few arguments to use on such idiots
    ?

    I can give you a real quick answer Konstantin: Katrina and Rita. I’d also refer them to this story by Reuters: LINK, which details that the first 6 months of 2007 had some of the severest weather on record.

    Comment by Steve Searls — 7 Aug 2007 @ 11:55 AM

  38. Probably off-topic, but I’d like to nominate Timothy Chase’s (#11) “permanent dustbowel in the [U.S.] Southwest” for typo of the month! It suggested a number of perfectly atrocious puns, all of which I was able to resist…

    Comment by George Peabody — 7 Aug 2007 @ 12:34 PM

  39. Answering David York in #34: You’re not wrong. Sorry!
    http://scrippsnews.ucsd.edu/Releases/?releaseID=761

    “… After correctly predicting in 1980 that global warming would be detected by 2000, Ramanathan observed at the end of the 20-year period that the amount of warming was roughly half what he’d predicted. The stifling of the warming trend is generally attributed to a counteracting cooling effect caused by global dimming, an inference that has since been supported by data collected by Ramanathan and others from a number of field campaigns.

    But what will happen when the counterbalance is eliminated? Already Western nations have been successful in reducing particulate pollution and Ramanathan believes emerging nations, most importantly in south Asia, will soon follow suit. As one form of pollution is eliminated, the mask concealing the true impact of global warming will be stripped away. He predicts an acceleration of warming trends to take place in coming decades but what that means for cloud formation, hydrological cycles and other events that affect albedo is unknown.

    “We’re sort of in uncharted territory when it comes to what happens 30 or 40 years from now,” Ramanathan said.

    Related to AGU Fall Meeting 2006 “Bjerknes Lecture: Global Dimming and Its Masking Effect on Global Warming”

    Comment by Hank Roberts — 7 Aug 2007 @ 12:34 PM

  40. The following article (and web site) might be of interest to RealClimate readers. I can’t vouch for the scientific accuracy/validity of the content (It does not seem to have undergone standard peer review, except by the editors. The author is a research scientist at the Institute of Environmental Physics / Remote Sensing (iup/ife) at the University of Bremen, Germany). But, the animations are kinda cool. Perhaps someone more qualified than I can comment?

    Visualization of the global distribution of greenhouse gases using satellite measurements, by Michael Buchwitz. The Encyclopedia of Earth. Posted July 31, 2007
    http://www.eoearth.org/article/Visualization_of_the_global_distribution_of_greenhouse_gases_using_satellite_measurements

    Comment by Chuck Booth — 7 Aug 2007 @ 12:38 PM

  41. Is there a statistical breakdown anywhere of what percentage of human behavior causes Global Warming?

    eg.

    Carbon Dioxide
    20% Automobiles
    15% Aircrafts
    30% coal power plants
    … etc

    Methane
    40% Bovine emittance
    20% Something else
    … etc

    Sorry but I’m a complete layman to what most of this site discusses as far as the science. I see a lot of knee-jerk reaction to what ‘we’ should to to combat Global Warming. I think it would be more prudent to at least focus the public on fixing the worst offenders.

    Comment by Michael Farinha — 7 Aug 2007 @ 12:45 PM

  42. Chuck Booth (#37) wrote:

    Visualization of the global distribution of greenhouse gases using satellite measurements, by Michael Buchwitz. The Encyclopedia of Earth. Posted July 31, 2007
    http://www.eoearth.org/article/Visualization_of_the_global_distribution_of_greenhouse_gases_using_satellite_measurements

    You can find more at:

    University of Bremen IUP/IFE SCIAMACHY WFM-DOAS: Main page
    http://www.iup.uni-bremen.de/sciamachy/NIR_NADIR_WFM_DOAS/

    Comment by Timothy Chase — 7 Aug 2007 @ 12:58 PM

  43. Michael F Is there a statistical breakdown anywhere of what percentage of human behavior causes Global Warming?

    How could they answer that when no one even knows how much of the warming is due to CO2 or methane and when there is absolutely no way to account for all of the various feedbacks (notably, of course, including the ones that they haven’t thought of or don’t know about)?

    It would be a bit like asking the hurricane forecasters how many of the 19 named storms last year were due to factor X. Both rely HEAVILY on theoretical models which give ballpark figures, and which, obviously, can be dramatically inaccurate. They’re lucky if they are usably accurate, let alone able to account for the effects of particular trace gases.

    Comment by DaveS — 7 Aug 2007 @ 1:31 PM

  44. George Peabody (#38) wrote:

    Probably off-topic, but I’d like to nominate Timothy Chase’s (#11) “permanent dustbowel in the [U.S.] Southwest” for typo of the month! It suggested a number of perfectly atrocious puns, all of which I was able to resist…

    Much appreciated!

    Unfortunately spelling was never one of my strengths – and my wife tells me that I took German just long enough for it to mangle my English grammar… In contrast, my wife lost a spelling “B” on account of reading too many British novels as a child – but she probably would have done just fine in Great Britain.

    Comment by Timothy Chase — 7 Aug 2007 @ 1:51 PM

  45. RE David York (#34)…

    How about BAU with carbon dioxide buildup partially masked by aerosol-induced global dimming, building climate crisis leading to a major economic recession? No more global dimming – followed by the full effects of several more decades of high levels of CO2 emissions.

    Comment by Timothy Chase — 7 Aug 2007 @ 2:08 PM

  46. I’m not saying to get numbers to show that 10% of x causes global warming. But rather since carbon dioxide, for example, is generally accepted as one of the leading causes of Global Warming we should be able to come up with a somewhat accurate estimate of where all the carbon dioxide comes from.

    I’m not trying to debunk anything. It just gets me when people like Danny Bee say “the world needs to stop all car and plane transport right NOW, for a one year test run,” I shake my head.

    If car & plane transport causes, lets say, 5% of the worlds ‘carbon footprint’ and coal plants are 40% of the carbon footprint. Then focusing solely on cars & planes would be folly.

    [Response: The data are available at the Energy information Administration, and are roughly for CO2 30% power stations, 30% transportation, and 30% industrial and residential. However, you really need to break it down by sector and include the other greenhouse gases - there is a nice graphic of this in a paper I saw recently, I'll see if I can't find it and post it here.... - gavin]

    Comment by Michael Farinha — 7 Aug 2007 @ 2:14 PM

  47. “This means that there is an upward surface flux of LW around (~390 W/m2), while the outward flux at the top of the atmosphere (TOA) is roughly equivalent to the net solar radiation coming in (1-a)S/4 (~240 W/m2). Thus there is a large amount of LW absorbed by the atmosphere (around 150 W/m2) – a number that would be zero in the absence of any greenhouse substances.

    A more useful factor gives ~0.75 ºC/(W/m2).”
    —————————————————————————————–
    From Stefan-Boltzmann we get an Earth temperature with no greenhouse gasses;-

    T4 = [1,368 W/m2 x (0.69)]/4s ; so T = 254 K or -19° Celsius

    So the 150 W/m2 , we calculate that the Earths temperature is 150*0.75 + -19° Celsius. That is the earths average temperature is 93.5° Celsius. However, this is not the case.
    With an average temperature of 15° Celsius, forcing is going to be 15+19/150 ºC/(W/m2) or 0.225 ºC/(W/m2); 2*CO2 could maximally give 5 W/m2 gives a max of 1 ºC.

    ——————————————————————————————

    [Response: You can't take any value that has the same units as the radiative forcing and multiply it by the sensitivity and expect to get anything sensible. For one thing, the 150 W/m2 net LW absorption includes all feedbacks already, secondly expecting climate sensitivity to be linear from no greenhouse gases to today's level is rather optimistic. Bottom line, you can't estimate sensitivity from the mean conditions today - you need to look at a climate change. - gavin]

    Comment by DocMartyn — 7 Aug 2007 @ 2:50 PM

  48. DaveS -
    How are we as a society supposed to curb our ‘carbon footprint’ if we don’t have at least a moderate grasp as to which parts of our society/lifestyles is to blame? When I see people like Danny Bee suggest “the world needs to stop all car and plane transport right NOW, for a one year test run,” I shake my head. That is not a solution to this problem. If someone were actually able to impose such a restriction I can guarantee you that the death toll across the world from a lack of food and resources would far outweigh any benefit (for mankind) it would cause in the reduction of Global Warming.

    With all the politicking around Global Warming I think it would behoove us to know which culprits to focus our efforts on first. Otherwise it will be like taking a stab in the dark… and we don’t want to stab ourselves in the process.

    Chuck B -
    Thanks for the link but just knowing that the USA is responsible for xx% of greenhouse gases doesn’t help me as a citizen make an informed decision on how I can best help. If you could say, for example, the USA is responsible for 40% of the worlds greenhouse gases with 4% from automobiles, 6% from aircraft, 35% from coal power plants, etc… then I, and society, can focus on the worst offenders first.

    Supposing that my above statistics are correct It would be more prudent for society to rally around reforming our coal power plants more so than around car’s and airplanes.

    I was a business major so my line of thinking is more on a return on investment wavelength. :-) Put most of your effort where you will be most effective.

    Comment by Michael Farinha — 7 Aug 2007 @ 2:55 PM

  49. My understanding is the CO2 effect is small. It is then amplified by increased water vapour in the atmosphere resulting from the warming caused by the CO2.

    What’s the CO2 effect alone at current CO2 levels in degrees C rise?

    What evidence is there that the amplification only works for CO2 produced warming, and not some other small warming?

    [Response: Feedbacks work for everything. That's why the 'radiative forcing' concept works - it doesn't matter if the initial push is from greenhouse gases or the sun. The change in temperature you'd need to balance a forcing of 4 W/m2 with no feedbacks is around 1.2 ºC and the difference between that and the real sensitivity (around 3 ºC) is a measure of how strong the net feedbacks are. - gavin]

    Comment by N Leaton — 7 Aug 2007 @ 3:43 PM

  50. Re #48: Michael Farinha — I recommend you follow

    http://biopact.com

    to discover where many billions of $$ are being usefully spent to provide biomass derived energy sources, for the benifit of many peoples.

    You’ll also find that the blog authors have opinions about which strategies are useful and which are less so…

    Comment by David B. Benson — 7 Aug 2007 @ 3:56 PM

  51. I’ve received email–and I’m not even a climatologist–from someone who’s a denier or denialist because he’s trying to think of this as a black-body radiation problem. The guy even did an experiment with painted ping-pong balls to convince himself that AGW must not be happening.

    That’s the wrong approach–and I wish people would stop and do their homework before trying to apply high-school physics to this–but it’s instructive. You can’t say “QED” until you’ve put together at least some two-layer radiative balance equations and shown how this actually works.

    Comment by Ben Kalafut — 7 Aug 2007 @ 4:14 PM

  52. Thanks for the link David B.

    Comment by Michael Farinha — 7 Aug 2007 @ 4:39 PM

  53. Comments on #5, #7 and #19

    First, can anyone be surprised about the state of confusion on AGW among the members of the (under educated) general public after reading the comments here?

    As a TV weatherman in Cincinnati, OH, USA I run into the problem of attribution constantly. In fact in January 2007 after a very unusually warm month I made the statement that this very warm month cannot be necessarily attributed to GW. Jan. 2007 was 5.3F (9.5C) warmer than normal. I stated long term records were stronger evidence for the effect and proceeded to present the 1.0F increase in mean temperature for the previous decade as evidence in support of GW, stating that AGW is likely a part.

    Following that was an avalanche of emails telling me to read Michael Crichton’s recent book, to stop taking issue with the Bush administration’s position, to stop advocating the destruction of the American automotive industry and on and on ad infinitum even though I made no statements about automobiles or Mr. Bush.

    What is the point?

    First people in accordance with Abraham Maslow’s “hierarchy of needs” will worry about putting food on the table first and global warming second, and second only if those of us concerned about the issue properly present the supporting arguments.

    If we present confusing information or forcefully and without consideration present information that overtly threatens a person’s well being (as that person perceives it) we have lost our audience.

    To Aaron Lewis (comment #5)

    Well…. are there other factors? Is AGW the only factor involved in the flooding in England? If as you seem to imply that AGW is the only factor in these storms how do you account for the great storm of November 1703. It may not have had as much rain as the event under discussion but it devastated southern England. It had to derive its energy from some source and the 1703 storm occurred long before anthropogenic global warming kicked into high gear.

    Please do not accuse me of being absurd here. My point is that it is much more complicated than Aaron states. Many factors always contribute to a particular event and in fact there are nonlinear, chaotic and linear feedbacks and interactions at a continuum of time and space scales from the nanosecond and molecule to the multi-century and global in every weather event.

    Steve Reynolds (comment #7)

    I agree more with you than with Gavin’s comment in reply to you. You are clearly saying that if we find no Katrina magnitude hurricanes in the past then maybe Katrina is a child of AGW. However historically there have been many hurricanes that equal or exceed the magnitude of recent hurricanes. Hurricanes require multiple minimum thresholds be surpassed to attain a given magnitude so unless the thresholds other than AGW are shown to be unimportant in a particular event then one cannot claim AGW is the sole cause.

    Be careful, this does not say that there is no role of AGW in the increase of hurricane strength it merely states that more work must be done to demonstrate how important a role.

    As I read Gavin’s comment it looks to me like he is not requiring a rigorous enough standard be met to make the case for the DOMINANT role of AGW. If on the other hand Gavin is just saying that a continuous chain of cause and effect need be followed to state SOME role of AGW in an event then I agree with him.

    From Terry Gilliam and his movie “Brazil”,

    “…even the complications have complications…”

    Bob Bergen (comment #19)

    I too teach, in my case introductory meteorology and oceanography. It seems weather and oceans have much more appeal than chemistry and physics so I get the less mathematically inclined students who are surprisingly naive about math being necessary for a detailed study of the atmosphere or ocean.

    Yes, as I have argued in earlier comments, even something as simple as sigma*T**4 will send most students into a math panic. I cannot use basic trig functions to explain the effect of sun angle on radiation intensity at the surface. Just wait until you try to describe kinetic theory and life at the scale of a molecule.

    I have, with mixed success, tried to avoid math altogether and teach conceptually. I know heresy! But I am faced with two choices: fail most of them or make the best of reality and have them leave with an intuitive knowledge of the physical world.

    Think of it this way, what is the mathematical description of a phenomenon without an underlying concept. The concept comes first the formalization after that.

    Gavin, for a career scientist to whom the concepts of basic atmospheric physics have become second nature and to whom the mathematics describing the phenomena can be read as clearly as a popular novel, I imagine it is very hard to understand that the level of mathematical competence in the general populace is so removed from yours.

    After teaching part-time for nearly 30 years I have seen a remarkable decline in the ability of students to deal with even basic math and have gradually, for introductory and non-major courses only, migrated to a conceptual approach.

    That is the first mountain to climb and once I accepted conceptual teaching the second mountain was separating unnecessary details from the core general concept. Of course one person’s unnecessary detail is another’s foundation cornerstone.

    It is a continuing challenge.

    Steve Horstmeyer

    Comment by Steve Horstmeyer — 7 Aug 2007 @ 5:03 PM

  54. Post #29 raises a good point. The simple toy model referenced is not easy to follow. The author doesn’t “show the work”. He should, it’s algebra. In my simple greenhouse model (see link below) I work through the issues step by step.

    My model is naive, clouds are treated as opaque radiation screens (like carports) and the cloud-free atmosphere is treated as a pane of translucent glass. Nevertheless, with a single adjustable parameter (chosen to make the forcing for a doubling in CO2 equal to 5.35) it produces a predication of 2.8 C for a doubling of CO2, which is very close to the consensus of far more complex models. That is, it does a good job with sensitivity (without any effort on my part ot make it do this).

    I ignore oceanic damping, except to estimate the size of the solar forcing from a putative solar cycle-linked temperature effect. And I don’t consider other greenhouse gases. I plan to add improvements as I come to understand the phenomena (this is complicated stuff). Most importantly I currently include the cosmic ray mechanism that skeptics like to cite and show that it doesn’t help their case.

    One of the reasons I have developed my model is because I found that most web resources dealing with AGW are either extremely watered down or way over my head. I have a Ph.D. in chemical engineering so my head isn’t *that* low. So I have sought to produce a model that gives pretty good results that an intelligent citizen with some math and science background can actually work through (with some effort).

    I still have some problems with figures on Internet explorer (it works with Firefox) that I am trying to fix. Anyways I would appreciate comments at malexan@sbcglobal.net

    Simple climate model: http://my.net-link.net/~malexan/Climate-Model.htm

    Comment by Mike Alexander — 7 Aug 2007 @ 5:14 PM

  55. “You can’t take any value that has the same units as the radiative forcing and multiply it by the sensitivity and expect to get anything sensible. For one thing, the 150 W/m2 net LW absorption includes all feedbacks already, secondly expecting climate sensitivity to be linear from no greenhouse gases to today’s level is rather optimistic. Bottom line, you can’t estimate sensitivity from the mean conditions today – you need to look at a climate change. – gavin”

    Ah, feedbacks, yes. Pretty models not tested by experimental data.

    But you do estimate sensitivity using a rule of thumb:
    “As we have discussed previously, the last glacial period is a good example of a large forcing (~7 W/m2 from ice sheets, greenhouse gases, dust and vegetation) giving a large temperature response (~5 ºC) and implying a sensitivity of about 3ºC (with substantial error bars).”

    The fact that CO2 was not the trigger for the change in the Earths temperature, is ignored.

    [Response: Not ignored, irrelevant. And if you weren't paying attention, none of the values come from models, all of it is from observational constraints. - gavin]

    Comment by DocMartyn — 7 Aug 2007 @ 5:20 PM

  56. You based the 3ºC on:-

    1) An analysis of the last glacial period which you now appear to believe was CO2 driven (if not then it adds nothing to effects of CO2 on temperature).

    2) a paper which used Bayes’ Theorem to analyse all the various gusses in the literature. Models Gavin.

    [Response: Your reading of this is bizarre to say the least. The LGM example does not depend on what leads or lags - it is an equilibrium calculation - read Lorius et al 1991, or Hansen et al 2006 for more details - part of the forcing is GHGs, part is not. Second point: Bayes Theorem is not a GCM, and none of the estimates used in AH06 were model based either. - gavin]

    Comment by DocMartyn — 7 Aug 2007 @ 6:42 PM

  57. Re:44 Timothy Chase
    Now you have gone and misspelled “spelling B” (its Bee), which is almost as funny as dust bowel :)

    Comment by B Buckner — 7 Aug 2007 @ 7:34 PM

  58. Thank you for this article. In point 4 you said “Most of the uncertainty is related to aerosol effects”. This of course is one of the points that Lindzen appears quite troubled by. In his 2005 article Is there a basis for global warming alarm?, Lindzen says “Unfortunately, the properties of aerosols are largely unknown. In the present instance, therefore, aerosols constitute simply another adjustable parameter (indeed, both its magnitude and its time history are adjustable).” In the same article he also says “aerosols and their impact are unknown to a factor of ten or more; indeed, even the sign is in doubt.”

    Are you able to point me to resources that set out how the net cooling affect of aerosols has been calculated? Also, are you able to tell me what the accepted estimate of the degree of uncertainty associated with net cooling affect of aerosols? Is it the factor of “ten or more” that Lindzen suggests?

    Comment by Svet — 7 Aug 2007 @ 7:55 PM

  59. Gavin: In step 4 you state: “The stratosphere reacts very quickly to changes in that (radiation) balance and that changes the TOA forcing by a small but non-negligible amount. The surface response, which is much slower, therefore reacts more proportionately to the ‘adjusted’ forcing and this is generally what is used in lieu of the instantaneous forcing.”

    Temperatures in the lower stratosphere stopped going down in 1993 according to published UAH, RSS and HadAT2 data series. Since the stratosphere reacts very quickly to changes in the radiation balance, shouldn’t the temperatures there continue to decline as CO2 builds up in the atmosphere?

    [Response: Lower stratospheric temperatures (as measured by MSU4) are dominated by ozone trends, with a large contribution from volcanoes, but only a minor effect from CO2. Further up in the stratosphere, cooling is much larger and continues apace. - gavin]

    Comment by B Buckner — 7 Aug 2007 @ 8:17 PM

  60. Even though the United States has not adopted a mandated reduction in carbon dioxide emmissions, at least a lot of people are still speaking about the issue.

    Comment by Chirs Moran CPA — 7 Aug 2007 @ 9:20 PM

  61. Steve Horstmeyer> Be careful, this does not say that there is no role of AGW in the increase of hurricane strength it merely states that more work must be done to demonstrate how important a role.

    I certainly agree. AGW will have many effects, some bad, some good. Having a scientific understanding of these effects (and the associated economics) seems very important to me. Unfortunately, too many here appear unwilling to consider that some short term ‘solutions’ could cause more harm than the original problem.

    Comment by Steve Reynolds — 7 Aug 2007 @ 10:09 PM

  62. Chuck Booth (#40) wrote:

    Visualization of the global distribution of greenhouse gases using satellite measurements, by Michael Buchwitz. The Encyclopedia of Earth. Posted July 31, 2007
    http://www.eoearth.org/article/Visualization_of_the_global_distribution_of_greenhouse_gases_using_satellite_measurements

    European Space Agency?!

    This is whats coming out of NASA:

    Atmospheric InfraRed Sounder – some of the vids I mentioned…

    AIRS – Multimedia: Videos: Animations
    http://airs.jpl.nasa.gov/Multimedia/VideosAnimations/

    Total Column Ozone Time Series – 8/1/2005 to 9/30/2005
    Carbon Monoxide Time Series – 8/1/2005 to 9/30/2005
    Water Vapor Time Series – 8/1/2005 to 9/30/2005
    Atmospheric Temperature Time Series – 8/1/2005 to 9/30/2005
    Outgoing Longwave Radiation Time Series – 8/1/2005 to 9/30/2005
    Cloud Fraction Time Series – 8/1/2005 to 9/30/2005
    A 3D Look At Atmospheric Water Wapor
    Supertyphoon Pongsona
    Supertyphoon Pongsona Isotherms
    Hurricane Isabel Isotherms
    Transport of Dust from China Dust Storm of April 2006
    The Alaska Fire Season of 2004
    Upper Tropospheric Water Vapor
    Atmospheric Temperature at 500 millibars

    … and vids on how its done:

    From Data Collection Swath to Atmospheric Temperature Profile
    Light Travels Through AIRS Optics
    False Color Thermal Images From AIRS channels In Three Spectral Regions

    Anyway, this sort of thing might help – as it demonstrates that absorption and reemission takes place throughout the atmosphere – and that it is fairly well understood.

    Comment by Timothy Chase — 7 Aug 2007 @ 10:19 PM

  63. Re #16 and Gerhard Gerlich, Ralf D. Tscheuschner. Falsification of the atmospheric CO2 greenhouse effects within the frame of physics.
    This runs to ~90 pages, the first 40 of which are devoted to proving that real greenhouses rely on cutting off convection rather than differential radiation effects! The authors seem very proud of themselves and slip in several very non scientific sneers as well. They consider the IR portion of the solar spectrum to be the same as the IR of the thermal radiation from the earth, they don’t seem to consider the TOA at all (I may have missed it in all the verbiage).
    The conclusion:
    “The point discussed here was to answer the question, whether the supposed atmospheric
    effect has a physical basis. This is not the case. In summary, there is no atmospheric
    greenhouse effect, in particular CO2 -greenhouse effect, in theoretical physics and engineering
    thermodynamics. Thus it is illegitimate to deduce predictions which provide a consulting
    solution for economics and intergovernmental policy.
    The authors express their hope that in the schools around the world the fundamentals of
    physics will be taught correctly and not by using award-winning “Al Gore” movies shocking
    every straight physicist by confusing absorption/emission with reflection, by confusing the
    tropopause with the ionosphere, and by confusing microwaves with shortwave.”

    Comment by Phil. Felton — 8 Aug 2007 @ 1:00 AM

  64. It seems like quite a number of posters here are looking for an easy-to-understand explanation for why increasing CO2 is a significant problem. Perhaps someone would be happy to oblige.

    Comment by PHE — 8 Aug 2007 @ 1:34 AM

  65. Re #53 Attribution (Steve Horstmeyer)

    You might want to use the loaded dice analogy in the attribution debate (discussed earlier on this site). If we throw a few sixes in a row, that would be consistent with a fair dice. However, 10 sixes in a row would start to raise some eyebrows.

    Also you may point at setting of records. For numbers drawn from a non-changing distribution, the chance of setting a new record (say an extremely hot summer) quickly goes down to zero after the first few records. If we keep on seeing new records, clearly something is the matter, and a new record hot summer may reasonably be attributed to GW.

    Comment by Dick Veldkamp — 8 Aug 2007 @ 4:08 AM

  66. [[As the environmental effects of global warming increase, the disruption to the economy will be far worse than that caused by banning the use of unnecessary transport.]]

    Alastair, I can go along with banning UNNECESSARY transport. But if you look at what I was responding to, the original poster was suggesting banning ALL transport, which is idiotic and would kill almost everybody on Earth.

    Comment by Barton Paul Levenson — 8 Aug 2007 @ 4:58 AM

  67. [[According to the Wikipedia source, the value for earth’s albedo is 0,3 only because clouds are taking into account. The albedo is about a third lower without the clouds (earth’s surface = 70% water).

    Is it allowed to use part of the atmosphere in this kind of calculations?

    Thanks.]]

    Yes. Clouds reflect away much of the sunlight reflected by the Earth, and they do cut down on how much sunlight is absorbed by the Earth system.

    You only have to deal with the albedo of the surface if you’re doing a model involving the surface plus layers of air. One value often used for the surface albedo is 0.10, which is an average including land, sea, and ice. The Moon, which has no sea or ice, has an albedo of 0.11, and Mercury, ditto (though it may have small amounts of ice near its poles) is about 0.119.

    Comment by Barton Paul Levenson — 8 Aug 2007 @ 5:02 AM

  68. RE #48 [Supposing that my above statistics are correct It would be more prudent for society to rally around reforming our coal power plants more so than around car’s and airplanes.]

    We have to think about what sources are growing fastest as well. For example, air travel is responsible for a relatively small proportion of current global CO2 emissions (though a larger proportion of warming because of other effects), but its projected growth, which would far outpace any likely efficiency savings, and which governments are encouraging, would make it one of the main CO2 sources in a few decades.

    Comment by Nick Gotts — 8 Aug 2007 @ 5:06 AM

  69. RE #66 (Barton Paul Levenson) [[[[As the environmental effects of global warming increase, the disruption to the economy will be far worse than that caused by banning the use of unnecessary transport.]]

    Alastair, I can go along with banning UNNECESSARY transport. But if you look at what I was responding to, the original poster was suggesting banning ALL transport, which is idiotic and would kill almost everybody on Earth.]]

    No, the original post #10 specified “all car and plane transport”. Not trucks, buses, trains or ships. This doesn’t mean it’s a practicable suggestion, but it’s not obviously crazy, as your misinterpretation here and in #23 would suggest. Given a few months to prepare, I’d guess it would be possible without insupportable disruption. The impossibility is political rather than economic.

    Comment by Nick Gotts — 8 Aug 2007 @ 8:30 AM

  70. Re #16 Check out: http://en.wikipedia.org/wiki/European_Science_and_Environment_Forum

    As far as Tscheuschner is concerned he must be wanting to torpedo his academic reputation for being associated with such rubbish.

    Comment by Lawrence McLean — 8 Aug 2007 @ 8:31 AM

  71. Re #69 Sorry, rereading #10 it’s internally inconsistent, at another point saying “all plane and vehicular transport”. And it does say NOW.

    Comment by Nick Gotts — 8 Aug 2007 @ 8:35 AM

  72. I hope our hosts will forgive me for continuing the somewhat off-topic policy discussion.

    Michael Farinha #48: Your impulse to focus on ROI is a good one, but be cautious in prioritizing mitigation efforts according to sectoral contribution. Generally, reductions should be prioritized according to what can be done at the lowest marginal cost. For example, say reductions can be realized by changing certain agricultural practices at cost of $5/ton of co2 equivalent or in the electrical utility sector at $10/ton. Even though the agricultural sector contributes a relatively small portion of GHGs it’s more efficient to makes these investments first.

    The best way of determining lowest cost reductions is through market instruments such as a tax or cap and tradable emissions permits regime.

    The overall sectoral emissions contribution can be a rough guide for inclusion in the mitigation regime but the most important element of the public policy (IMHO) is to apply a nontrivial price on emissions wherever it’s administratively cost-effective and allow for market mechanisms to “find” low cost reductions. Emissions offsets/tax credits allow for reductions to be realized outside of the cap or tax regime.

    Comment by Andre Arbour — 8 Aug 2007 @ 9:41 AM

  73. Gavin,

    Some remarks on several points in this step program:

    - No problems with steps 1-3.

    - Step 4:
    The efficacies calculated in the Hansen report are within the constraints of the model used. Accoding to Hansen, the efficacy of e.g. solar is 0.9 that of CO2. Hardly to believe, as a test of the HadCM3 model (see here shows that solar may be underestimated with a factor 2.
    In the case of HadCM3, the model included a fixed value for aerosols effect, without that, the difference might have been larger.

    Indeed aerosol effects are quite important, one can halve the efficacy of CO2 in a simple model (Oxford EBM model), if the real forcing (or efficacy or both) of aerosols is lower than expected, without changing the temperature profile of the past century (see here).
    The global cooling effect of aerosols indeed is questionable: Ramanathan found (published in Nature) that the current aerosols above India (and probably China, as they use a lot of dirty coal) are increasing the warming with about 50%. India and China are also the largest contributors to SO2 at this moment. This makes the “cooling” effect of aerosols in general rather dubious…

    [Response: This is both wrong and irrelevant. All aerosols cause local heating (due mainly to absorbed LW), and the Asian Brown Cloud additionally has strong absorption of solar due to the presence of black carbon. Sulphates however are a cooling. The stott et al study does not show any differences in efficacy in any case. - gavin]

    - Step 5:
    As said in the previous point, there are problems with the attribution of efficacies. The main difference between solar and volcanic at one side and GHGs and (man-made) aerosols at the other side is their distribution effect and the kind of radiation.
    Incoming solar radiation has two important effects: heating of the stratosphere (mainly in the tropics) and deep penetration of the oceans. Downwelling radiation from GHGs is more distributed all over the latitudes and absorbed in the upper fraction of a mm of the ocean’s surface. The effect of the different radiation spectra on clouds is another item of interest…
    From solar it is known that the stratospheric warming shifts the jet stream position, cloud cover (regional and global) and rain patterns (USA, Italy, Portugal, recently South Africa) to the poles and back together with the solar cycle. From GHGs, the influence on these items is not known to any accuracy (especially cloud cover…). Stratospheric dust from volcanoes has the opposite effect of solar. But man-made aerosols should have their maximum cooling effect in the NH (90% of the emissions), where most of the increase in temperature is found…
    Most of the ocean warming is found in the sub-tropics (see fig.2 in Levitus), which is mainly caused by changes in cloud cover, inducing 2 W/m2 more insolation in the (sub)tropics over the past 15 years. This is more probably attributable to natural causes (solar or internal terrestrial) than GHGs.

    About the attribution of the different efficacies in the last ice age, again this is questionable: the start of the last ice age, at the end of the Eemian, was without any help of CO2 (maybe with some help of methane). Temperature was down near minimum, before CO2 levels started to decrease (see here, without much change in temperature when CO2 started to decline (with 40 ppmv).
    Moreover, the Epica C ice core doesn’t show any sign of positive feedback from CO2 for the whole LGM-Holocene transition. I know from my former work as process engineer how a positive (and a runaway!) feedback looks like… See here. Anyway, this points to a much smaller effect of 2xCO2, compared to the other forcings/feedbacks like insolation, ice sheet albedo, vegetation growth,…

    [Response: The reason why we look at the LGM is that it is at equilibrium. All of these other issues involve transients where we do not have complete information for what was changing when. Your last line perhaps reveals your confusion. Sensitivity comes from examining all forcings together and for the LGM it includes ice sheet albedo, vegetation and GHGs. - gavin]

    - Step 6.
    Based on the former remarks, the formula for future warming may not be a simple (sum of forcings) x (general sensitivity) but a sum of (each forcing x its own sensitivity)…
    Which makes it a little more difficult (but more exiting) for climate modelers…

    [Response: To show that this would make a significant difference you have to demonstrate that efficacies are indeed substantially different from unity (for which there is no evidence) - gavin]

    Comment by Ferdinand Engelbeen — 8 Aug 2007 @ 10:22 AM

  74. > http://en.wikipedia.org/wiki/European_Science_and_Environment_Forum
    Oh, ick. I’d forgotten. Shudder.

    Comment by Hank Roberts — 8 Aug 2007 @ 10:24 AM

  75. I don’t see step 5 as “easy”. For one thing it doesn’t point to a paper or explanation of sensitivity, rather a section. From the section I gather that correlations in climate history are used to derive sensitivity. The biggest problem with doing that is the smoothing and other time distortions in the proxies for CO2 and temperature make them only useful for longer time periods.
    So using them to predict short term catastrophe (100 years) without detailed weather models is not going to be particularly useful.

    Comment by Eric (skeptic) — 8 Aug 2007 @ 11:10 AM

  76. I think that you really need to step back at the beginning and give a broad overview of *why* quantum mechanics and radiative transfer work the way they do. I’m an astronomer, and radiative transfer is a tool that we employ all of the time. There are subtle things that are, in my experience with students, significant conceptual blocks. You’re assuming a lot of prior knowledge here, and I’d begin with the following:

    1. For a first approximation the Earth can be treated as being in radiative equilibrium; this is a state where the incoming energy from the Sun is balanced by the outgoing energy radiated by the Earth.

    2. Both the Sun and Earth emit light at all wavelengths (or colors, or energies). The temperature influences both how much total light is emitted (the Stefan-Boltzmann law) and what the typical energy of the light is (Wien’s law). The Sun has a surface temperature of 5770 Kelvin, so most of it’s energy is emitted in the form of visible light; the Earth has a surface temperature of about 300 K, so most of it’s energy is emitted in infrared light.

    3. Molecules and atoms absorb only certain wavelengths, or colors, of light. This is a fundamental feature of quantum mechanics that can be precisely measured in the laboratory. The atmosphere is very transparent to visible light, which allows sunlight to reach the surface and warm the Earth (with the exception of clouds). However, the molecules in the atmosphere absorb infrared light, and each distinct molecule (water, carbon dioxide, methane, etc.) will absorb different wavelengths of infrared light.

    4. When light emitted by the Earth is absorbed by a gas its energy either goes into heating the gas (by collisions between the molecules) or is re-emitted in a random direction (which can include reflecting it back to the surface.) In either case absorption reduces how much heat the Earth can put out, which would drive it out of radiative equilbrium. To compensate the Earth gets hotter, causing it to emit more light. This is the “greenhouse effect.”

    5. When light is absorbed by the atmosphere there are two distinct stages. As you add more of something (like CO2), the initial effect is to efficiently absorb certain wavelengths of light. However, once you have enough of an absorber then it is already blocking pretty much everything that it can, and the net effect of adding more becomes progressively smaller. This is why species like methane or carbon dioxide (which are much less abundant than water) matter; they fill in the transparent windows between windows in the spectrum that are blocked by water.

    Comment by Marc — 8 Aug 2007 @ 11:27 AM

  77. I agree with #5 that weathermen do a disservice by suggesting certain severe weather events expected in a GW world cannot be attributed to GW. While this may be technically true, since GW & its effects are at a higher order level of statistics & not single events, it grossly misleads the viewing public, who tend to interpret it as “GW is not happening.”

    So weathermen could (if they wanted to be honest in spirit, not just technically) say, “Hurricane XXX (or this flood, or brush fire) adds one more piece of evidence that GW is happening.” A piece of evidence (an observation in a statistical data set) out of context of the rest of the evidence does not a case or statistic make, so the statement (I think) would be techically accurate (i.e., no claim is being made that the hurricane by itself proves GW, it just adds one more observation to the data set that is already on the whole linked to GW), especially since GW at the macro-statistical level has already been established. The statement would be accurate both technically and in the spirit of not misleading people into rejecting the idea of global warming.

    RE #19, I don’t think one needs any math to understand GW. The greenhouse is a good heuristic device (or a closed car sitting in the sun). Another is a prism, which shows light in many colors (that ought to dazzle them); and it can be explained that certain bands (the ones that generate heat — and we all know from daily experience that the sun generates not only light, but also heat) have longer wavelengths and tend to bounce back, rather than go through, and that the GHGs up in the sky tend to bounce these heat bands back to earth …. Water acts as a prism, and so does air (with the molecules in it). And then there is the black cloth/white cloth experiment re which absorbs more heat.

    Numbers are for the professional number crunchers. It can be said that it may get hot enough by the time your children (or grandchildren) are old to melt enough glaciers and ice sheets and to raise the sea above New York’s (or Houston’s) ground level….Or other non-numerical scenarios….

    Comment by Lynn Vincentnathan — 8 Aug 2007 @ 11:49 AM

  78. [Response: Feedbacks work for everything. That’s why the ‘radiative forcing’ concept works - it doesn’t matter if the initial push is from greenhouse gases or the sun. The change in temperature you’d need to balance a forcing of 4 W/m2 with no feedbacks is around 1.2 ºC and the difference between that and the real sensitivity (around 3 ºC) is a measure of how strong the net feedbacks are. - gavin]

    Ok. So what percentage of the 3C change is just down to the CO2, and what is down to the feedback effects?

    In the IPCC report, from what I can tell, the small increase for solar radiation includes no feedback effect, but the figure for CO2 does include feedback effects.

    Is this correct?

    [Response: No. All the forcings in the AR4 figure are without any feedbacks. Feedbacks only go into the calculation of the sensitivity. If you have a forcing from solar or CO2 of 4 W/m2, then you would need to change the temperatures by 1.2 deg C (keeping everything else constant) to restore balance. However, everything else is never constant and the feedbacks multiply this 'no-feedback' temperature by about 2.5. The no-feedback response is therefore 40% of the total. But remember this factor is the pretty much the same for a solar forcing as it is for CO2. - gavin]

    Comment by N Leaton — 8 Aug 2007 @ 12:08 PM

  79. Re #53
    Dear Steve,

    Thank you for your concern about the teaching of math and science. Perhaps if we did a better job of teaching math and science we would not be facing the current situation.

    My concern about AGW is about the survival of the infrastructure required for civilization. A nomadic herding tribe can survive violent changes in climate. However, civilizations engineer structures based on their experience with the local climate. If the climate changes, then that infrastructure fails. If too much of a civilization’s infrastructure fails, then that civilization fails.

    The British know how to build infrastructures that will withstand huge monsoon rains. They learned that in India. However, their experience with the climate in Britain did not lead them to apply such engineering to the structures in Britain. They had a good reason, in the past, it would have been a waste of capital.

    The problem with AGW is that it invalidates our long experience with local climate. This disrupts our asset allocation and engineering processes. AGW increases the frequency of the most intense storms. Such storms cause damage to infrastructure engineered to modern standards where capital cost is a major concern. (Low bid mentality)

    If we deny AGW, then storm damaged infrastructure is rebuilt to the old standard on the assumption such storms occur rarely, when in fact, as a result of AGW, such storms are now occurring more frequently, and can be expected much more frequently in the future, as the full effects of AGW unfold.

    Such building and rebuilding will result in a huge waste of capital. We do not have capital to waste. We have to build to withstand the storms expected to be produced by the climate of the future rather than the climate of the past. That can be a very expensive proposition. For example, it is hugely more expensive to build a house to withstand a cat. 3 hurricane than to build a house to withstand a cat. 1 hurricane. On the other hand, it is much cheaper to build one house that can withstand a cat 3 hurricane then to build a cheaper house, and have it blow down, killing the family inside.

    Now, as an experienced weather forecaster, what is your advice to the stakeholders planning public infrastructure?

    Comment by Aaron Lewis — 8 Aug 2007 @ 12:26 PM

  80. re 69

    “Given a few months to prepare, I’d guess it would be possible without insupportable disruption. The impossibility is political rather than economic.”

    One thing for sure: muscle-powered locomotion would definitely come into vogue. Get a good lock for your bicycles, kiddies – they’ll be worth their weight in gold.

    On a related note, I think the economic factors are equally difficult to surmount. Consider – my local supermarket is selling oranges grown in Australia. Now, the last time I checked, Australia is in the midst of a severe drought with no end in sight. Yet they are shipping their water to the U.S. in the form of oranges and who knows what else. Which begs the question: what is really wrong with this picture? I enjoy winter – and summer – veggies as much as the next guy, but how much do we want to really pay for this enjoyment, long-term?

    re: 10

    “Planet is in DIRE DIRE straights….”

    Minor quibble. The planet is NOT in dire straits; it is the state and content biosphere we depend upon for our existence. The planet and life in general will continue on quite nicely with or without us, thank you very much, though as a member of an interested species, I would prefer the former to the latter.

    Comment by J.S. McIntyre — 8 Aug 2007 @ 12:47 PM

  81. As a ‘physics for poets’ style explanation of the greenhouse effect and ancillary feedbacks, I like to use an empirical comparison with the Moon, using simple arithmetic.

    This gives a rough difference of about -35C for an earth stripped of atmosphere, icecaps, oceans, vegetation and clouds, assuming an average earth temperature of ~12C over the last 400,000yrs, which fairly approximates the derivation from Boltzman’s Law, and additionally demonstrates the buffering affect against temperature extremes relative to a near vacuum environment.

    A gross over-simplification of a complex system, but it does provide an intuitive handle for those without a scientific/mathematical education.

    Comment by luminous beauty — 8 Aug 2007 @ 12:52 PM

  82. re 77
    Weather models used by forecasters reflect surface sea temperatures that are above historical norms.

    Why are the SST warmer now, than in the past? AGW is an (unspoken) assumption of every modern weatherman.

    Comment by Aaron Lewis — 8 Aug 2007 @ 1:02 PM

  83. To add to my previous comment, the Cheshire cat smile the weathermen when they say the temp is “below average” also is a disservice. It reconfirms the skeptics that GW is not happening, since the temp today is below average. (Average of what is another side issue — the last 2 years?)

    They could now and then point out that although the temp today is below average, the daily temps go up and down (above and below and just about average), but the overall trend over the years and around the world is increasing temperatures due to GW.

    They could now and then take a brief moment to mention aspects of GW. Enquiring minds want to know. Perhaps the local news could get other sponsors, besides oil and car companies. I never ever ever hear weathermen where I live now in S. Texas mention the words “global warming” or “climate change” — but that’s an improvement since a Chicago weatherman (brother of an Enron guy) used to say global warming is NOT happening, at least up until 2002 when we left the area.

    Comment by Lynn Vincentnathan — 8 Aug 2007 @ 1:25 PM

  84. I hope Marc will keep working on this explanation from the astronomer’s point of view. Note that the definition of “light”– to an astronomer — includes infrared!

    Comment by Hank Roberts — 8 Aug 2007 @ 1:44 PM

  85. Re #60 –

    “Even though the United States has not adopted a mandated reduction in carbon dioxide emmissions, at least a lot of people are still speaking about the issue.”

    People are doing more than “speaking”. I’ve been looking at cost savings from energy efficiencies a lot over the past few months (ROI strongly favors just ditching energy wasting products — so strongly I’ve learned to not worry so much about cost, and now save enough that the $400 rechargeable mower I just bought will be paid off in 9 months or less from what I save now on lighting. It’s just insane.), and what I see is a severe shortage of products (a sign of demand outstripping supply), or a major increase in variety (a sign of healthy demand being met by supply). That’s a good sign that people are DOING a lot.

    I forget the conversion rate (someone here can supply, I’m sure), but in the last several months I think I’ve avoided something on the order of 2 megawatt-hours of electric consumption. There are still a lot of people who’ve not jumped on the CFL bandwagon yet, but based on what I see in stores, a lot of people have already. Multiply those people by 4 or 5 (or more) megawatt-hours saved per year and you’re talking more than a small reduction in CO2 emitted. If you check the news in regards to declining US car manufacturer market (we make more gas guzzlers than the Japanese), and the increase in Japanese market share, I’d wager there is a shift in national fleet fuel economy as well — and if we could just kill all the SUV owners, we’d be golden.

    Comment by FurryCatHerder — 8 Aug 2007 @ 2:10 PM

  86. re: #68, #69, Nick

    I recommend David Strahan’s, “The Last Oil Shock: A Survival Guide to the Imminent Extinction of Petroleum Man” (2007), which can be ordered from Amazon in UK or Canada, but not in US. You can get some of it from http://www.davidstrahan.com/. It misses some issues, but overall is pretty readable.

    Given that Hubbert’s Peak for world oil = 2015 (+/- 5 years, depending on reality level of OPEC numbers), it seems unlikely that the amount of air travel is going to keep going up for very long. If it does, it means somebody will be converting a lot of coal to kerosene, not A Good Thing for The Climate. Note that petroleum (down) may not be a good thing if it means (unsequestered) coal (up).

    Comment by John Mashey — 8 Aug 2007 @ 2:14 PM

  87. Re: #16, “According to the second law of thermodynamics …”

    Oh, NOW I get it. The same people who believe the earth is only a few thousand years old, deny evolution, and don’t believe people cause global warming, also don’t believe the Sun is a giant fusion reactor 93 million miles away. The sun is really a god who mounts his chariot at the gates of dawn every morning, rides across the sky, and then descends into the underworld at night.

    This makes the Sun an atmospheric phenomenon, which means it is part of the “planetary system”, which means it is a closed system, which means the 2nd law of TD applies, which mean AGW isn’t possible!

    Q-E-bloody-D

    Comment by shargash — 8 Aug 2007 @ 2:20 PM

  88. Comments to Lynn Vincentnathan (comments #77 and #83)

    I get the feeling your approach would be applauded by the nay-sayers concerning AGW – generalize and lump all TV weathermen into one category – talk about confusing the issue. The nay-sayers do the same with “climate scientists”. Stereotypes will do nothing but come back to haunt anyone who uses them to argue a concept that should be based on fact and specifically cited instances. I have spent too much time in my career educating the public to let you get away with that. At the same time I will not defend American television’s abysmal record when it comes to informing the public.

    I know nothing about you Lynn but it sure seems to me that you have done very little in the way of trying to explain complex issues in a clear and general way in a time-constrained format. Basically we must use the K-I-S-S approach (i.e. keep it simple stupid. With the widespread use of the web we can drive the audience to sources of good information so then can learn more.

    Am I the only one who is asking why you are surprised that you hear nothing about global warming from TV weathercasts now? You live in south Texas what do you expect in an environment where oil is so important? Call your local TV weathercasters (the gender neutral term I prefer that also does not imply each and every one is educated as a meteorologist) and ask them if they are permitted by management to address the issue of AGW. You may be surprised! I am lucky I have no such constraints.

    FYI when a TV weathercaster (meteorologist or other) says the temperature is below average they are using the internationally recognized definition based on a 30 year period of record. That period of record changes every 10 years.

    Currently “average” is based on the 30 year period 1971 – 2000 and next it will be based on the 1981 – 2010 thirty year period.

    To add a bit of confusion to the mix “average” is different from “climatic normal”. Because 30 values of high temperature for May 4th, for example, are too prone to influence by a single extreme value the data are fit to a mathematical function called a spline which stabilizes the data. A simple example of why this is necessary: If May 4th 1988 had a high temperature 30 degrees below average it would change the 30 year average by 1 degree. It is then possible that May 4th could have a lower average high temperature than May 3rd or even April 30th for the 30 year period. At that time of year the long-term average high temp is rising each day and over a sufficiently long period of record the “average” will not decline but rise steadily. The influence of that single observation would not be so great in a 150 year data base. That single May day with a high temperature 30 degrees below average would have an influence of 30/150 or 0.2 degree. (All temperature references in °F).

    It is likely that most TV weathecasters do not know which (average or climatic normal) they are speaking about and a good bet they do not know the difference.

    Dick Veldkamp (comment #65)- good suggestions and also nicely pointed out in “An Inconvenient Truth”. Thanks for the suggestion.

    Steve Reynolds (comment #61) – great point, my favorite of the short term “solutions” with potential for damage from unintended consequences is seeding the ocean with iron filings to sequester CO2.

    Steve Horstmeyer

    Comment by Steve Horstmeyer — 8 Aug 2007 @ 2:54 PM

  89. The IPCC use the diagram on p4 of this doc. to illustrate their position http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch01.pdf perhaps someone can point out the important points of comparison with the “Six Easy Steps”

    Comment by Dermod O'Reilly — 8 Aug 2007 @ 3:18 PM

  90. Re # 76 “The Sun has a surface temperature of 5770 Kelvin, so most of it’s energy is emitted in the form of visible light”

    I’m afraid that is not true – visible light makes up less than 50% of the emitted solar radiation. http://earthobservatory.nasa.gov/Library/SORCE/sorce_02.html

    Comment by Chuck Booth — 8 Aug 2007 @ 3:37 PM

  91. The peak of the solar spectrum is in the visible, and just under half is pretty close to most. (Technical point: how you do your accounting also depends on whether you count photons or energy). I do agree that you should communicate that the Sun emits all sorts of light, and that UV, visible, and IR differ only in energy and wavelength.

    In a guide like the original proposed one, you have an overall goal. One very common question that I get from students is about why the greenhouse effect is one way – why does light from the Sun get in and light from the Earth get out? It does help to know that there are predictable rules that explain why sunlight is different from the light emitted by the Earth.

    Comment by Marc — 8 Aug 2007 @ 3:57 PM

  92. Bob Bergen’s comment in,#19, that he has college freshmen reading at a tenth grade level and that have little or no math background, and Hank Roberts comment,in #27 That John and Jane Q Public are too distracted or too apathetic to take time to get on speaking terms with climate change, worries me almost as much as AGW. Perhaps we’re not challenging our kids enough in high school. PBS ran a docu drama some years ago about a math teacher in California teaching calculus to high school kids from a poor neighborhoods with remarkable success. The kids even enjoyed it! I hope we don’t have to have a 9/11 equivalent or a Pearl Harbor, to wake people up.

    If the North Atlantic Conveyor Belt turns off, or arctic permafrost melts and suddenly releases huge amounts of methane, I don’t think you’ll have to dumb down the conversation to anybody!

    Comment by Lawrence Brown — 8 Aug 2007 @ 4:07 PM

  93. Here’s what climate scientists are up against: (I’m glad someone is saying it.)

    Gore: Polluters manipulate climate info

    By Gillian Wong, Associated Press
    SINGAPORE — Research aimed at disputing the scientific consensus on global warming is part of a huge public misinformation campaign funded by some of the world’s largest carbon polluters, former Vice President Al Gore said Tuesday.
    “There has been an organized campaign, financed to the tune of about $10 million a year from some of the largest carbon polluters, to create the impression that there is disagreement in the scientific community,” Gore said at a forum in Singapore. “In actuality, there is very little disagreement.”

    Gore likened the campaign to the millions of dollars spent by U.S. tobacco companies years ago on creating the appearance of scientific debate on smoking’s harmful effects.
    (read more)

    http://www.usatoday.com/tech/science/environment/2007-08-07-gore-climate-change-manipulation_N.htm

    Comment by catman306 — 8 Aug 2007 @ 4:14 PM

  94. Re #73 (comment)

    Gavin,

    Is there any period in history which can prove that different forcings have the same sensitivity of 0.75 K/W/m2? All I can see is that in most periods, including ice ages/interglacials, there is a huge overlap of forcings, where CO2 in the past was a feedback of temperature changes. And the above sensitivity is based mainly on solar/insolation changes (at least initially). Which isn’t necessarely similar for CO2 or other greenhouse gases.

    The overlap of forcings makes the attribution of real sensitivities quite difficult, as we have one dependent variable (temperature) and four more or less independent variables (solar, GHGs, tropospheric and stratospheric aerosols). I know, there are some attribution attempts, but these depend very much on the pre-industrial reconstruction chosen as comparison…

    [Response: Effectively yes. The response to volcanic eruptions has been used to determine sensitivity - that is relatively clean, volcanic+solar was used by Crowley (2000) and Hegerl et al (2006), the transient effects of GHGs+ ice sheets was looked at in Hansen's latest. The PETM CO2+CH4 estimates and response were looked at by in a paper of mine (though you get a reasonable match, that isn't as good a constraint). All of these are consistent with efficacies close to unity. - gavin]

    Comment by Ferdinand Engelbeen — 8 Aug 2007 @ 4:19 PM

  95. Re comment number 2 by Mike Alexander one possible explanation for why the early 20th century temperature rise was so big compared to the post-fifties warming is the rebound from cooling imposed by three large volcanic eruptions with a long gap thereafter until 1991:
    KRAKATAU Indonesia 1883 Aug 27 VEI 6
    SANTA MARIA Guatemala 1902 Oct 24 VEI (probable 6)
    NOVARUPTA Alaska Peninsula 1912 Jun 6 VEI 6

    PINATUBO Luzon (Philippines) 1991 Jun 15 VEI 6

    from Large Holocene Eruptions table by Smithsonian Global volcanism program, http://www.volcano.si.edu/world/largeeruptions.cfm

    Comment by Don Condliffe — 8 Aug 2007 @ 4:41 PM

  96. Powering the Planet, by Nathan S. Lewis, is certainly a forceful, sobering read. At least read the last two paragraphs.

    http://EandS.caltech.edu/ESarchive-frame.html

    and download the first featured pdf file.

    Comment by David B. Benson — 8 Aug 2007 @ 4:53 PM

  97. re: 93

    Seeing as you brought up the environment, I’d like to mention the absolutely marvelous time I am having reading Alan Weisman’s new book “‘The World Without Us” and recommend it accordingly.

    I originally read a short excerpt a year or so ago in Discover magazine wherein Weisman described how, as I recall, New York would eventually disappear, beginning to disintegrate almost immediately upon the disappearance of the humans needed to maintain its infrastructure. I picked the book up upon its release expecting more of the same – you know, the crumbling majesty of man’s works, the exposure of the weakness of our technology, the inability of our monuments to actually endure without us, and to a satisfying degree I got what I paid for.

    But that is only the icing on the cake. This is a truly clever book, both in structure and execution. It would appear the author has engaged a particularly subversive technique in selling his book (discussion of mankind’s demise and its effect on the planet, something that has a perverse appeal, IMHO, to human psychology) in order to discuss something much more immediate: the fragile environmental state of affairs we find ourselves in at the beginning of the 21st century.

    The set-up is delightful: in order to first discuss what the world would be like without us, one first must discuss what the world was like before we arrived and built our civilization, and then examine how the world has changed due to our civilization’s “footprint”. Only then can you have a contextual reference from which to understand the effect of our passing.

    Thus, in very clear and accessible language, Weisman details how we have really made a mess of things – and global warming is part of the discussion, on more than one level – without ever appearing to lecture his reader. I would suggest this (seriously) as a gift book for people who are on the fence or just a little over the other side on these issues. I think it one of the best ways to get people to see the damage we are doing to ourselves without engaging in arguments or to pleading with them to “read this and you’ll understand!” knowing all the while they won’t.

    Instead, appeal to that perversely morbid curiosity I mentioned, that odd conceit that makes humans wonder what survives past their deaths. The only downside: it can be a disquieting read in the sense of how thoroughly he lays out a case for how badly we have been mucking up our world.

    Comment by J.S. McIntyre — 8 Aug 2007 @ 5:35 PM

  98. Re: #89

    There really aren’t many points of comparison, as the figure you cited is an estimate of the earth’s CURRENT energy budget and the post concerns CHANGES in that budget.

    Comment by Jerry Steffens — 8 Aug 2007 @ 6:08 PM

  99. Re: #41 Where does the CO2 come from?

    This chart (World Resources Institute: GHG Emissions Flow Chart) gives a very nice overview of what contributes what to what (as it were).

    [Response: Yes! that was the graph I was thinking of. Thanks! - gavin]

    Comment by Gareth — 8 Aug 2007 @ 6:46 PM

  100. Re 99
    I feel like I am arguing over how many angels can stand on the head of a pin, but I strongly suspect that chart under reports nitrogen oxides.

    Most fuel combustion produces some NOx. Then, more are produced by organic free radicals in hot exhaust flows. Some of these compounds have significant greenhouse gas properties.

    Thus, while the percentage of NOx produced is small, the size of the underlying flows and their importance as greenhouse gases suggest that NOx from transportation, residential, and commercial buildings should be visible flows on the chart.

    Note that auto emissions form a concentrated layer just above a (black asphalt) road surface making a perfect small scale heat trap. The effect of such a heat trap will not be captured in climate models. the emmissons form buildings will be concentrted in urban areas. Does this explain some small part of the urban heat island effect?

    [Response: NOx compounds are most important climatically as ozone precursors, rather than greenhouse gases in their own right. See the previous posting... - gavin]

    Comment by Aaron Lewis — 8 Aug 2007 @ 8:06 PM

  101. Maybe I missed it but I didn’t see anything in this post about water vapor or clouds.

    I know it was a post about CO2 but isn’t much the green house effect an enhancement of effect of CO2 caused by water wapor?

    Comment by Jim Cross — 8 Aug 2007 @ 8:09 PM

  102. An interesting “toy model” was published by Svante Arrehenius in 1896 and his conclusions about the “carbonic gases” has proven to be one of the most prescient papers ever written.

    Comment by Ray Hoff — 8 Aug 2007 @ 8:30 PM

  103. Re # 91 Marc,
    With all due respect, I’m afraid I (a biologist) don’t understand how you (an astronomer) can state, with respect to the emission spectrum of solar radiation that “just under half is pretty close to most.” And yes, the peak emission is in the so-called wavelengths, but so what? Integrating (even crudely, by eyeball) the area under the energy emission spectrum (and I was referring to energy flux, Watts per cm^2 per sec – not photon flux)reveals that visible wavelenths make up about as much as IR and UV combined. Stating this fact shouldn’t complicate explanations of the “greenhouse effect.”

    My experience teaching science to non-science major college students (mostly freshman and sophomores) for over two decades hasn’t been quite as exasperating as it apparently has for others who have posted here. But, I’ve usually found it better to simplify complex topics by withholding information rather than simplifying to the point of being incorrect, or relying on flawed analogies (unless I state clearly why a particular analogy is just that, and not a scientific explanation). Students come to class with enough misconceptions – I don’t want to introduce more by telling them things that aren’t true (Funny how obviously flawed analogies seem to sink in much more readily than correct scientific explanations).

    Comment by Chuck Booth — 8 Aug 2007 @ 9:58 PM

  104. Are you able to point me to resources that set out how the net cooling affect of aerosols has been calculated? Also, are you able to tell me what the accepted estimate of the degree of uncertainty associated with net cooling affect of aerosols?

    Comment by Svet — 8 Aug 2007 @ 10:30 PM

  105. “We often get requests to provide an easy-to-understand explanation for why increasing CO2 is a significant problem without relying on climate models and we are generally happy to oblige.”

    Yet you did NOT. You rely on climate models for the key numeric values for the strenghts of different forcings and sensitivities.

    [Response: Not so. LBL codes are not climate models, and the sensitivity is from observational constraints. Please read the relevant papers. - gavin]

    And I noticed GiSS have adjusted their estimations for average annual temperatures in the United States due to the great work done by Watts, McIntyre and initially Pielke. As a result the hockey stick won’t have a blade soon, and 4 of the warmest years on record are from 1930′s now. 1998 has lost it’s place as the warmest year on record, and 1934 now holds that position. And soon you will be trying to get the models to simulate trends for 0.xx degrees less warming. Shouldn’t you be thankful to them (people you have derailed in the past in realclimate articles), that the science is getting more accurate? Or are you disappointed with these developments?

    [Response: All improvements are of course welcome. However, this had nothing to do Watts or Pielke, and the global mean temperatures are basically unaffected (since the problem was only with US temperatures which cover less than 2% of the globe). No changes in the models will happen because of this. - gavin]

    Comparing your communication of your research to the likes of Pielke, is like comparind a night to a day. You are so certain, so convinced and showing next to no doubt, while e.g. Pielke comes across as open minded, uncertain and full of doubt. Which of the two is the more scientific approach?

    [edit]

    I’m seriously concerned that we will spend thousands of billions on something that isn’t necessarily a problem to begin with, while as a result neglegting many real concerns because our resources are limited. These include bio-diversity loss, ocean depletion and water shortage.

    It’s not a win win situation. If unimaginable amounts are used to combat “global warming” and in the end it is proven that there wasn’t a serious initial problem to start with, people will ask questions about how those thousands of billions could have been spent more productively for the good of mankind. I hope you then won’t have any explaining to do about the sincerity, openness and scientific integrity of your research.

    Comment by CAGW skeptic — 9 Aug 2007 @ 2:32 AM

  106. Step 5 may be facing some challenges here:

    http://earth.myfastforum.org/about56.html

    [Response: Not really. - gavin]

    Comment by andre — 9 Aug 2007 @ 5:30 AM

  107. I think this article is important, in terms of the motivation for this particular post and the site as a whole: What matters most in politics – facts and logic, or stories and feelings?

    I see a lot of facts and figures in the “easy-to-understand” explanation. I’m also not sure of the necessity of the steps 4-6 in such an explanation.

    There has to be a simpler way of making these arguments.

    One interesting thing I came across is the idea of “lies-to-children”*. I think it was in the Pratchett, Stewart and Cohen book about “science” where they said that much of science education consisted of a series of “lies-to-children” in which they were not told the complete truth. When students got to the next level of education they would then be told “You were taught x, but, actually, it’s more complicated than that…”

    One thing we have to understand is that we are never going to convince the tiny, but loud, minority of nutjob denialists. calmly pointing out their dishonesty is important, but not if it comes at the expense of talking to the not particularly interested majority. They’ll get bored by the details, and use incessant arguing about them to justify not giving a damn.

    * A “lie-to-children” is the sort of thing you tell a small child who asks lots of questions about the world. It isn’t possible to tell them the whole truth, because they won’t understand it, but you can tell them something that approximates the truth.

    Comment by Timothy — 9 Aug 2007 @ 5:58 AM

  108. RE: 104

    A recent theory has proposed that the Younger Dryas may be associated with a comet impact striking the North American ice sheets.

    http://www.newswise.com/articles/view/530208/

    Comment by Jim Cross — 9 Aug 2007 @ 6:02 AM

  109. [[The planet is NOT in dire straits; it is the state and content biosphere we depend upon for our existence. The planet and life in general will continue on quite nicely with or without us, thank you very much, though as a member of an interested species, I would prefer the former to the latter.]]

    This isn’t really correct. We’re in the middle of a mass extinction that human technology has essentially caused and global warming will make much worse. Global warming is not just a problem for humans.

    Comment by Barton Paul Levenson — 9 Aug 2007 @ 6:07 AM

  110. Hi all

    Any comment on the latest revelations at climateaudit.org on the revelations regarding the USHCN Data Set.

    Regards
    Peter Bickle

    [Response: McIntyre noticed that there was an odd offset in the GISTEMP analysis in 2000 which turned out to be related to the transition between USHCN data to the GHCN data. The offset occurred because the USHCN corrections (for Time of Observation bias mainly) affect the more recent values in USHCN but not GHCN (as opposed to only affecting earlier values). Once notified of the problem, GISS investigated immediately, found the error, and added an extra step to the analysis to remove any jump at the transition. This only affected the US temperatures (reducing the mean by about 0.15 ºC in 2000-2006), but since the US is such a small part of the world, it doesn't effect the global temperatures. Note that this wasn't a problem with the USHCN data - rather in how the different data sources are melded. It also had nothing to do with any micro-site issues. - gavin]

    Comment by Peter Bickle — 9 Aug 2007 @ 6:38 AM

  111. “This only affected the US temperatures (reducing the mean by about 0.15 ºC in 2000-2006), but since the US is such a small part of the world, it doesn’t effect the global temperatures.”

    You make it sound like, it was no big deal. What’s 0.15C between friends, eh? And how do you know such problems are only restricted to the USA? Perhaps there are worse problems elsewhere?

    After the adjustments 1934 is now the hottest year on record after a 3/4 century of CO2 emissions. Now what did you say was the climate sensitivity for a doubling of CO2? a) 3.0C b) Perhaps 2.5C or c) To be honest, you don’t know exactly?

    [Response: 1934 is the warmest US year. Globally 2005 was the warmest year in GISS and NCDC, 1998 in the CRU analysis. And you appear to be mistaking me for someone else if you think I ever claimed to know the climate sensitivity 'exactly'. - gavin]

    Comment by CAGW skeptic — 9 Aug 2007 @ 7:23 AM

  112. This only affected the US temperatures (reducing the mean by about 0.15 ºC in 2000-2006), but since the US is such a small part of the world, it doesn’t effect the global temperatures. Note that this wasn’t a problem with the USHCN data – rather in how the different data sources are melded. It also had nothing to do with any micro-site issues. – gavin]

    That’s a big conclusion that isn’t justified.

    One of the largest sets of data is the US.

    With this error, it isn’t a small percentage of the world’s temperature that is the issue. It is that the US data is a large percentage of the data available.

    Nick

    [Response: But the global average isn't simply an average of all the stations divided by the number of stations. You need to adjust for area so that a high concentration of stations in one spot doesn't bias the mean. If the US is 2% of the area, then a 0.15 ºC correction there implies only a 0.15*0.02=0.003 ºC correction to the global mean (though it's actually a little higher because of incomplete global coverage). These things should obviously be fixed, but the implications need to be kept in perspective. - gavin]

    Comment by Nick — 9 Aug 2007 @ 7:31 AM

  113. “Not so.”

    What is this then:

    “experience with more sophisticated GCMs suggests that…”

    I don’t think you are saying that you count the actual forcings and sensitivies independently of the hugely complex mechanisms of the atmosphere / climate? For an example, different AGM’s cited by the IPCC offer everything between 1.4C and 6.4C for the climate sensitivity of doubling of CO2. What is the worth of a value that is theoretized with no consideration for the huge complexity and countless mechanisms that affect the climate? And when you consider them, you have to model it to the best of your ability, to make some sense of it, isn’t that right? Or alternatively just hold your hands up.

    I don’t think anyone denies that CO2 affects the climate. The question is how much. I’m sure the so called “denialists” would basically agree with everything else here except “3.0C”.

    The northern hemisphere should have warmed more than the southern (e.g. New Zealand observed no warming during the 20th century), this is how the theory goes. Now you do little adjustments, and you find out it was even a bit warmer in 1930′s than in the first decade of the 21st century. And don’t say it is just 2%. The US is bit more than just 2% of the land area in the Northern hemisphere, and representative of an even larger area.

    No noticeable increase in temperature in 75+ years of CO2 emissions. And who knows if the current mean temperatures will come down a little bit more, when the sites have been surveyed.

    Then there’s Pielke and dozens of his colleagues who say that land use change is a major climate forcing, which they say have been neglected by the IPCC and the AGM modellers. Then there are another dozen or more uncertainty factors.

    You cannot possibly confidently state an accurate number for the doubling of atmospheric CO2. That makes no sense. It is far beyond our current capacity.

    Comment by CAGW skeptic — 9 Aug 2007 @ 7:49 AM

  114. Re #111 [[After the adjustments 1934 is now the hottest year on record after a 3/4 century of CO2 emissions. Now what did you say was the climate sensitivity for a doubling of CO2? a) 3.0C b) Perhaps 2.5C or c) To be honest, you don’t know exactly?

    [Response: 1934 is the warmest US year. Globally 2005 was the warmest year in GISS and NCDC, 1998 in the CRU analysis. And you appear to be mistaking me for someone else if you think I ever claimed to know the climate sensitivity ‘exactly’. - gavin]]]

    Gavin, I’m afraid you’re forgetting, here and in your responses to #110 and #112, that nothing outside the USA really counts :-)

    Comment by Nick Gotts — 9 Aug 2007 @ 7:53 AM

  115. “you appear to be mistaking me for someone else if you think I ever claimed to know the climate sensitivity ‘exactly’.”

    Didn’t you just say:

    “Climate sensitivity is around 3ºC for a doubling of CO2″

    ?? What am I missing here?

    [Response: A dictionary? - gavin]

    Comment by CAGW skeptic — 9 Aug 2007 @ 7:54 AM

  116. re 109

    [[The planet is NOT in dire straits; it is the state and content biosphere we depend upon for our existence. The planet and life in general will continue on quite nicely with or without us, thank you very much, though as a member of an interested species, I would prefer the former to the latter.]]

    This isn’t really correct. We’re in the middle of a mass extinction that human technology has essentially caused and global warming will make much worse. Global warming is not just a problem for humans.

    You’ll forgive me if I disagree.

    While I have no arguement re the effects of global warming, my point was the biosphere has survived five mass extinctions so far and will likely survive the current one, if that is what it turns out to be (and I believe it is, for what it is worth).

    Life WILL go on, most likely, until that day in the far future when the sun boils off our atmosphere – and like even then it will find a way within the crust and mantle. Not life as we recognize it in the here and now, perhaps, but it will go on.

    Comment by J.S. McIntyre — 9 Aug 2007 @ 10:38 AM

  117. Re: #113, “You cannot possibly confidently state an accurate number for the doubling of atmospheric CO2. That makes no sense. It is far beyond our current capacity.”

    CAGW skeptic, yes, you can. As atmospheric CO2 concentrations were roughly 275-280 ppm prior to 1850 (when we started to industrialise), we can say that a doubling of CO2 would lead to concentrations around 550-560 ppm. Simple mathematics.

    Comment by Stephen Berg — 9 Aug 2007 @ 10:53 AM

  118. Re: #105, “It’s not a win win situation. If unimaginable amounts are used to combat “global warming” and in the end it is proven that there wasn’t a serious initial problem to start with, people will ask questions about how those thousands of billions could have been spent more productively for the good of mankind.”

    CAGW skeptic, have you heard of the Stern Review on the Economics of Climate Change? It says investment in fighting the worst effects of climate change is necessary to prevent an economic disaster as a result of climate change.

    http://www.hm-treasury.gov.uk/independent_reviews/stern_review_economics_climate_change/sternreview_index.cfm

    A nice summary is here:

    http://en.wikipedia.org/wiki/Stern_Review

    Comment by Stephen Berg — 9 Aug 2007 @ 10:58 AM

  119. #67 Barton, A little idea, cloud albedo may reflect energy to space, but we often forget that clouds are rich in water vapour, which is a source of energy through latent heat of evaporation, I think that these clouds may have been underestimated as a source of heat, or rather the heat loss through cloud albedo (reflection of sunlight)is not the correct calculation of net heat loss since clouds themselves are a latent heat source.

    Comment by wayne davidson — 9 Aug 2007 @ 12:02 PM

  120. Re: # 105 CAGW skeptic

    “If unimaginable amounts are used to combat “global warming” – Who is suggesting that this is necessary?

    “people will ask questions about how those thousands of billions could have been spent more productively for the good of mankind” – Such questions are always asked about potentially expensive policy decisions, such as going to war.

    Comment by Chuck Booth — 9 Aug 2007 @ 12:08 PM

  121. Off-topic, and I apologize in advance. Just following up on an earlier commenter’s detour.

    #87– I recognize the humor in your comment, but you’d do well not to alienate the religious people who take interest in reading the comments on climate blogs. There are more religious people who believe in gravity, evolution, thermodynamics, relativity, the green house effect and the sun-god who traverses the sky by day and visits wrath upon the underworld by night than you seem to think there are.
    ———-

    [[One thing I’ve found over the years of dealing directly and indirectly with high school students is that the direct scientist-student route is not very productive (very different assumptions about what an explanation entails!). However, the scientist-teacher then teacher-student route is much more so. Teachers get the scientific points much faster and are also in a much better position (and have more patience) to lead the students to understanding. Therefore, maybe we could help each other out here.]]

    I think this is a terribly interesting piece of the puzzle to ponder–how best to bridge the gap between Scientist and lay person? It seems not so different from the problem of bridging the gap between Pope and lay person in some ways. (The biggest difference is, of course, that the Scientist is actually qualified to tell people about the errors of their ways, and how then to live in order to be saved!)

    And religion has a history of causing people to actually change their ways. (Granted, its not always a nice, pleasant story about some non-violent Mahatma starving himself to liberate his people from imperial tyranny or a Messiah choosing death on a cross in favor of attempting a coup.)

    The educational process is not getting the job done in the USA, and I think a grassroots movement is what is needed to actually change America’s behavior on CO2. And if there’s one group that in America today that can spark a grassroots movement, isn’t it the evangelical? Read this.

    The emerging rapprochement is regarded by some as a sign of how dramatically U.S. public sentiment has shifted on global warming in recent years. It also has begun, in modest ways, to transform how the two groups define themselves.

    “I did sense this is one of these issues where the church could take leadership, like with civil rights,” said Northland’s senior pastor, Joel C. Hunter. “It’s a matter of who speaks for evangelicals: Is it a broad range of voices on a broad range of issues, or a narrow range of voices?”

    Hunter has emerged among evangelicals as a pivotal advocate for cutting greenhouse gas emissions that scientists say are warming Earth’s climate.

    Comment by Christopher Pearl — 9 Aug 2007 @ 12:24 PM

  122. #119 Make that latent heat of condensation, A cloud 100 meter thick probably reflects just as much energy as a cloud 1000 meters thick. The difference is that one has more energy than the other…

    Comment by wayne davidson — 9 Aug 2007 @ 2:02 PM

  123. RE #111, The Dust Bowl was caused by global warming! I knew it! :)

    Comment by Lynn Vincentnathan — 9 Aug 2007 @ 2:40 PM

  124. Re #113, #115 and possibly others here regarding CO2 sensitivity.

    I don’t think anyone denies that CO2 affects the climate. The question is how much. I’m sure the so called “denialists” would basically agree with everything else here except “3.0C”.

    Didn’t you just say:

    “Climate sensitivity is around 3ºC for a doubling of CO2″

    ?? What am I missing here?

    You might like to read Camp and Tung (submitted to JGR)

    Seems the CO2 sensitivity is quantifiable and its value is being refined.

    No matter how you look at it, it seems to me, whether the actual value is skewed left, right, or not at all wrt the wide range arising from different model runs or Camp and Tung’s constrained range (95% confidence level, independent of models) for CO2 sensitivity (based on actual measurement data), the value is ~3°C for a doubling of CO2. Of course, this might change after peer review of the Camp and Tung paper has been completed. Think it unlikely though.

    And you might like to read Camp and Tung’s analysis of solar attribution of temperature variation and the 11 year cycle at GRL or here.

    Comment by P. Lewis — 9 Aug 2007 @ 3:16 PM

  125. Wayne, a cloud is droplets of liquid H20 that have lost some heat to the surrounding atmosphere. Water vapor is H20 in gas form, molecules that have enough energy that they don’t stick together as droplets. Not sure where you’re going with the notion of clouds having energy, but it’s all just bouncing around in the lower atmosphere at that level; only when the heat gets up to the top of the atmosphere can it radiate away.

    Comment by Hank Roberts — 9 Aug 2007 @ 3:18 PM

  126. #121, I can vouch that my church has not been much help re global warming (though some evangelicals & others (e.g., Green Lights Episcopalians) are doing things). I know Pope John Paul II told us in 1990 that it’s everyone’s responsibility to mitigate GW, and the U.S. Bishops in 2001 (what took ‘em so long?) said that prudence requires us to do so, but these statements haven’t translated into action or even change of heart in my parish. One “very religious” person even said the bishops might be wrong; another said, “we all have to die sometime” (to which I responded, yes, but we don’t have to kill); and the priest seriously considers Limbaugh’s views on GW & said he’s worried about what the Limbaugh Catholics in the parish might think if he broaches the GW topic. As with the government and media, churches are also tied into anti-environmental forces & evil money; for instance when our parish’s environmental committee was to put on an “eat low on the food chain” program, the beef guys on the parish council sent a message via the nun in charge to can it (we disobeyed, since the program was already set). And educational institutions are just as bad; my friend worked up a vegetarian day during Earth Week some years back at an Illinois community college, and the beef guys on the school board disallowed her from explaining how the veggie food the students were eating that day related to environmental issues.

    What that leaves us with, I’ve recently come to conclude, is Hollywood as our only hope against the corrupt institutions of our society :) They’re only into titilating and and luring the money-paying public, and their relationship with the public is more direct, not deflected by evil as much as the church-state-education-business-(non movie)media. And if Hollywood hasn’t provided us with enough GW movies and documentaries to effect significant GHG reductions, that’s only because the public has already been corrupted to a large extent by the other societal institutions. So that’s my latest macro-sociological analysis of the global warming situation :)

    Comment by Lynn Vincentnathan — 9 Aug 2007 @ 3:27 PM

  127. “the value is ~3°C for a doubling of CO2″

    In laboratory, in theory, or in complex reality?

    If we accept this value 3 degrees, then today it should be approx. a degree warmer than it was in 1930`s with all the CO2 we have put in the atmosphere. But it isn`t and the theoretical value breaks down there and then. There`s no decline in solar activity to compensate, aerosol effects are mostly local, and the atmosphere e.g. in USA has been getting clearer. You look at this data, and if you don`t doubt the 3C, then how do you explain that?

    [Response: Climate sensitivity is an equilibrium concept. Right now we are not at equilibrium (as evidenced by the increasing temperature rises and ongoing increases in ocean heat content). The oceans have a huge inertia and take time to warm up. As in Step 6, the warming seen so far is completely consistent with a sensitivity of about 3 ºC and a net heat imbalance (going mostly into the ocean) of about 0.6 W/m2. Think of that imbalance as the 'unrealised' forcing. So of the 1.6 W/m2 we think we've added to the system, only 1 W/m2 has been realised, and so we expect a warming of about 0.7 to 0.8 degrees. Pretty consistent, no? - gavin]

    Comment by CAGW skeptic — 9 Aug 2007 @ 4:01 PM

  128. “we expect a warming of about 0.7 to 0.8″

    That`s fine, except that current global temperatures are only around 0.2-0.3 warmer than in 1930`s if even that considering UHI effect and sudden 0.15C adjustments.

    Much/Most of the warming occurred in early 20th century.

    [Response: That's simply not true. Do the analysis yourself: http://www.giss.nasa.gov/gistemp - gavin]

    Comment by CAGW skeptic — 9 Aug 2007 @ 4:37 PM

  129. re 126 and the Catholic Church, I have to wonder at how credible the C Church is regarding doing anything about GW so long as they maintain an anti-contraceptive stance.

    That said, nice analysis….

    Comment by J.S. McIntyre — 9 Aug 2007 @ 4:47 PM

  130. Re#114:

    The northern hemisphere should have warmed more than the southern (e.g. New Zealand observed no warming during the 20th century).

    This is nonsense. Over the 20th century NZ warmed by at least 0.7C. Go here and scroll down to Fig 6.

    Your claim is eerily similar to one made by a local sceptic who claimed on the basis that a hot summer in Christchurch in the early 1900s was similar to a very cold summer in 2006 that there was no warming taking place. Complete bollocks, if you’ll pardon my anglo-saxon.

    And – sorry to go off topic, but could I suggest RC solicit an urgent post from a sea ice expert?

    From Cryosphere Today:

    Thursday, August 9, 2007 – New historic sea ice minimum
    Today, the Northern Hemisphere sea ice area broke the record for the lowest recorded ice area in recorded history. The new record came a full month before the historic summer minimum typically occurs. There is still a month or more of melt likely this year. It is therefore almost certain that the previous 2005 record will be annihilated by the final 2007 annual minima closer to the end of this summer.

    In previous record sea ice minima years, ice area anomalies were confined to certain sectors (N. Atlantic, Beaufort/Bering Sea, etc). The character of 2007′s sea ice melt is unique in that it is dramatic and covers the entire Arctic sector. Atlantic, Pacific and even the central Arctic sectors are showing large negative sea ice area anomalies

    Comment by Gareth — 9 Aug 2007 @ 5:49 PM

  131. [[Life WILL go on, most likely, until that day in the far future when the sun boils off our atmosphere - and like even then it will find a way within the crust and mantle. Not life as we recognize it in the here and now, perhaps, but it will go on.]]

    I sincerely doubt it. The next step after the habitable Earth is the runaway greenhouse Earth, about 0.6-1.4 billion years from now. Since life as we know it requires liquid water, that pretty much rules out life continuing on the Earth — unless, of course, we alter the climate at that time artificially.

    Comment by Barton Paul Levenson — 9 Aug 2007 @ 6:19 PM

  132. [[You might like to read Camp and Tung (submitted to JGR)]]

    Good paper overall, but in their estimation of the effect of changing solar constant, they seem to neglect the Earth’s albedo.

    Comment by Barton Paul Levenson — 9 Aug 2007 @ 6:24 PM

  133. Gareth, New Zealand experienced glacial advances between 1980`s and early 2000`s.

    GiSS and CRU disagree so much with each other, and often the samples are wholly inadequate, and then as a rule the derived mean temperatures are always high on the scale, that it`s very difficult to take them at a face value, if you are a rational person.

    These are presumably teams of highly skilled professionals, and then a single person like Steve McIntyre can spot a basic error which makes them adjust their mean temperatures by 0.15C and they pretend it`s nothing [edit]. I doubt these errors are restricted to the USA, because the sample data is less adequate in the rest of the world, and the modellers seem to have a fetish for deriving as high mean temperatures as possible. The less data you have, the higher the mean temperatures will be.

    They try to make fun of the surface station survey, but Anthony Watts has already proven how unreliable many of these stations are. The attitudes are more political than they are scientific. A scientist would be happy that someone is doing this job, so that we can have more accurate data, but these people seem to be genuinely afraid and annoyed that they will have to adjust the mean temperatures another 0.1C soon. And down on the scale of course, as everyone could have predicted.

    Comment by CAGW skeptic — 9 Aug 2007 @ 6:24 PM

  134. #130 Garreth. Yep its bad, never quite seen anything like this…

    #125 Hank, I’ve been looking for temperature variation reasons, knowing full well that 2007 started really warm, yet there was a recent small bit of cooling which I’ve detected independently from other more known temperature records which confirm the same thing (GissTemp, NOAA etc…), been trying to find where the energy has gone to, I have reasoned that its in the clouds, which are a mixture of vapour and droplets. Of which there is 600 Calories per gram of water vapour, no small figure considering the size Earth’s cloud areas. This greater cloud extent may have been indirectly proven by strong rain showers all over the world…….

    Comment by wayne davidson — 9 Aug 2007 @ 7:01 PM

  135. Re:#133:

    Gareth, New Zealand experienced glacial advances between 1980`s and early 2000`s.

    We also have glaciers that are in long term retreat. Proves nothing about warming or cooling, because glacial mass balance depends on more than just temperature.

    Comment by Gareth — 9 Aug 2007 @ 7:19 PM

  136. Wayne, re that recent plateau in temperature, New Scientist just published an article that mentions it; it turned up as one of the results of a new model using the Argo (sea temp) instrument data; I quoted an excerpt and gave a cite here.

    The original article is in the current Science: http://www.sciencemag.org/cgi/content/abstract/317/5839/796

    Excerpt I quoted from NS in the other topic is here:
    http://www.realclimate.org/index.php/archives/2007/07/green-and-armstrongs-scientific-forecast/langswitch_lang/sk#comment-45973

    Comment by Hank Roberts — 9 Aug 2007 @ 7:42 PM

  137. Thanks for the links Hank, variability is always there, it doesn’t mean we can’t explain it. There is also
    a certain planetary wave offset stemming from the all time low Polar ice as cited above, immediate consequences just been explored since the North Pole looks soo different now, its a new landscape.

    Comment by wayne davidson — 9 Aug 2007 @ 8:04 PM

  138. Re #133,

    The cyclical behavior of New Zealand’s glaciers on a decades timescale is nothing new. What matters is the long-term behavior. For example, see Figure 6 in this USGS reference:

    http://pubs.usgs.gov/pp/p1386h/nzealand/nzealand.html

    The short-term advances aren’t very impressive when superimposed on the long-term trend.

    Comment by spilgard — 9 Aug 2007 @ 8:22 PM

  139. #111 response: Globally 2005 was the warmest year in GISS

    Interesting that it appears that the year to July 2007 is the equal warmest year in GISS. One year is not statistically significant, of course.

    Comment by Chris O'Neill — 9 Aug 2007 @ 9:50 PM

  140. Re # 134 “… [specific heat of] 600 Calories per gram of water vapour”

    Wayne, You should be aware that your spelling of calorie with a capital C may be lead to confusion – nutritionists, dieticians, food manufacturers et al use Calorie (capital C) to represent kilocalorie. Of course, the SI unit is joule, rather than calorie, but that is another matter.

    Comment by Chuck Booth — 9 Aug 2007 @ 10:25 PM

  141. Re: [[Life WILL go on, most likely, until that day in the far future...]

    All well and good, I suppose, but you seem not understand that it’s ME going on, in reasonable comfort and so on, that I’m worried about :-) And to a somewhat lesser extent my friends and putative descendants.

    Comment by James — 10 Aug 2007 @ 1:08 AM

  142. Regarding New Zealand glacial advances:

    According to Chinn et al (2005) the cause of the advance in glaciers in New Zealand’s southern alps is primarily from changes in the global circulation, causing a strengthening of westerly circulation at those latitudes. This results in increasing precipitation over the glaciers and a decrease in ablation temperatures due to the increasing wind velocities.

    Much of the changes observed in the global circulation are thought (although the research is by no means conclusive) to be coincident with the currently observed climate change, which has anthropogenic factors as one of its driving sources.

    Meanwhile, there has been an overwhelming glacial retreat observed in the last decade. The retreat of the Greenland ice sheet has accelerated from 21.33 m (70 ft) per day to 33.5 m (110 ft) per day in the period from 2001 to 2005 (Howat et al. 2006).

    It would help if people would, before bringing these points out in a debate, to read the literature and get a rudimentary grasp of the topic at hand. You can be far more convincing this way.

    Comment by Chris C — 10 Aug 2007 @ 2:24 AM

  143. [[These are presumably teams of highly skilled professionals, and then a single person like Steve McIntyre can spot a basic error which makes them adjust their mean temperatures by 0.15C and they pretend it`s nothing [edit]. I doubt these errors are restricted to the USA, because the sample data is less adequate in the rest of the world, and the modellers seem to have a fetish for deriving as high mean temperatures as possible. The less data you have, the higher the mean temperatures will be.]]

    Global warming has also been detected in sea surface temperatures — are there urban heat islands on the ocean? It has been detected in boreholes — are there poorly sited temperature stations underground? It has been detected from balloon radiosonde data, satellite observations, melting glaciers, rising sea levels, tree lines moving toward the poles, animals migrating toward the poles, and on and on and on. Are you familiar with any of this evidence? What makes you think global warming will go away if you discredit the surface record?

    Comment by Barton Paul Levenson — 10 Aug 2007 @ 4:50 AM

  144. Re #98
    My problem with the link I found, http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch01.pdf is that it represents the IPCC position now. There are two important features, it includes evaporated heat tranfers an convection, neither of which are included in here. Further the IPCC diagram shows the atmosphere radiating 324W to the earth, in general the troposphere is colder than the surface, thus, as anyone knows, energy just doesn’t go this way.

    Comment by Dermod O'Reilly — 10 Aug 2007 @ 5:41 AM

  145. To #6 onstantin
    The surest thing about climate change is that it will change precipitation patterns. Some parts will be drier and some wetter. Hydro power is ridiculous without water and dam(n) dangerous with too much water. Riverside nuclear power stations are very dangerous if flooded or unsufficiently cooled.
    Agriculture, in rich or poor countries, can on average and over long time possibly adapt to climate change. But it can’t adapt to transients: if you’ve potatoes are rotting it is not much of a comfort that it would have been a great rice harvest.
    Both more and less water will mean a shorter life for buildings, as ground water table falls or rises. Kind of global Tower of Pisa, but not much of a tourist attraction if it happens pretty simultaneously in several millions of buildings, some of them skyscrapers. This last (buildings, water-tables) is however my own speculation -would be most grateful if anybody could find reviewed studies to confirm it.

    Comment by Fredrik Lundberg — 10 Aug 2007 @ 6:03 AM

  146. CAGW skeptic,

    According to an article I read recently, it appears that it is the older temperature records that have exagerated the temperatures higher than they really were. Apparently due to insufficient shielding from the sun.

    This is directly inverse from the line of resoning from folks like yourself who deny AGW.

    Anyone capable of observing reality, truely objectively, without distorting it via their desired reality, can see how dramatically the climate is warming.

    I have noticed that there is a story circulating that 1934 has now been given the record hottest US year. I am skeptical that would be the case, I doubt that a place as large as the US could be so far outside the warming trend that I observe in Australia. How long was the ice fishing season in 1934? How long in the last 5 winters? Does anyone have any concrete information regarding this story?

    Comment by Lawrence McLean — 10 Aug 2007 @ 9:29 AM

  147. re 131 –

    [[Life WILL go on, most likely, until that day in the far future when the sun boils off our atmosphere - and like even then it will find a way within the crust and mantle. Not life as we recognize it in the here and now, perhaps, but it will go on.]]

    You wrote: “I sincerely doubt it. The next step after the habitable Earth is the runaway greenhouse Earth, about 0.6-1.4 billion years from now. Since life as we know it requires liquid water, that pretty much rules out life continuing on the Earth — unless, of course, we alter the climate at that time artificially.”

    Not to nitpick (even though that’s exactly what I’m doing), but I was more or less saying that when I noted the sun would boil away our atmosphere, the assumption being a runaway greenhouse effect was a given. Of course, this does not mean life won’t survive in a runaway greenhouse world – we have no proof one way or the other and comments in that direction are at best speculation (but as I recall, if life exists withing the crust and mantle, it would still exist, tough obviously we’re not talking about complex life).

    My real point in my original and follow-up is that life in the biosphere will go on WITHOUT US – at least in the geologically measured short-term, in relation to the original comment regarding the planet being in trouble. It isn’t.

    “…unless, of course, we alter the climate at that time artificially.”

    Ah, but isn’t that the problem being discussed here? *grin*

    Seriously, I grew up in the age where we dreamed of expanding outward into the solar system and, somehow, some way, into the galaxy. As time has gone by I’ve become pessimistic of our odds of doing so. At the same time, it is becoming ever so much more apparent to me that, in the end, we may be faced with leaving the planet as the only hope of our continued existence. (particularly if we ever manage the feat of surviving that 0.6 billion years to where it becomes absolutely imperative that we do.)

    Regardless of who or what survives, we certainly have found ourselves in one heck of a pickle, as my dear, departed Grandmother was fond of saying.

    Have a happy Friday.

    Comment by J.S. McIntyre — 10 Aug 2007 @ 10:07 AM

  148. Re: [[Life WILL go on, most likely, until that day in the far future…]

    All well and good, I suppose, but you seem not understand that it’s ME going on, in reasonable comfort and so on, that I’m worried about And to a somewhat lesser extent my friends and putative descendants.

    ================

    Ah, but I do. I’ve a daughter and nieces and nephews that I wonder about constantly. It’s then when I find myself the most depressed about the outlook.

    Put another way, I think we’ve just passed what are, in many ways, some of the best years to be a human alive on this planet (if you are in the the right country and a decent economic situation, of course). Things may never be quite so good, particularly in terms of the environment and climate.

    One can’t help but feel the generations that follow aren’t being cheated.

    Comment by J.S. McIntyre — 10 Aug 2007 @ 10:11 AM

  149. Gavin,

    I was wondering about your numbers in Step 2. You stated that removing CO2 reduces the LW absorbed by 14% or 30 W/m2. Is this a result from the referenced papers? From the 150 W/m2 LW absorbed in Step 1, it would appear that 14% should be 21 W/m2. Thanks!

    [Response: Going back over the papers, you get around 30 W/m2 for clear sky profiles (i.e. the situation without clouds) (Kiehl and Trenberth, 1997). Ramanathan and Coakley (1979) have 12% decrease in all sky conditions, and Hansen et al 1988 (using a LBL model) have 14% - again in all sky conditions. In radiative forcing calculations, the instantaneous value is around 22 W/m2, while the adjusted value is closer to 30 W/m2. Some of these variations are related to the particular configuration or metric, while some is real uncertainty. For the sake of this argument, those details aren't particularly important and so a looser statement, such as 'between 20 and 30 W/m2' is probably fine. Thanks for pointing out the inconsistency. - gavin]

    Comment by Pete DeSanto — 10 Aug 2007 @ 1:08 PM

  150. Thanks Gavin. I appreciate your website and use it as a jumping off point to find references on many topics concerning climate science. It’s nice to see a discussion of the science without all of the political rhetoric (at least in the original posts!).

    Comment by Pete DeSanto — 10 Aug 2007 @ 2:11 PM

  151. How to simplify the presentation of the greenhouse effect? Most of the focus is on forcings, which I think is the wrong way to go. Forcings are a convenient tool for those who do science but not for layman. For a layman, the forcing concept makes intuitive sense if we are talking about changes in solar output, in which case the amount of radiation impinging the Earth would increase. But the greenhouse effect intuitively understood is not about making the sun act like it is brighter. It’s about the atmosphere more effectively trapping the fixed amount of energy the sun bestows upon the Earth.

    In my treatment of the greenhouse effect (see link on my name) I start with the radiation balance:

    S(1-A)/4 = 240 = e*sig*T^4

    where S is the solar constant, A is albedo, e is emissivity, sig is the S-B constant and T is absolute temperature in Kelvins. The solar constant is a well known parameter for which I use the rounded value of 1370 watts per sq meter. Sig is a constant (5.67e-8) and the albedo is 0.3. Average temperature is 15 C (288K) Plug all these in and you get e = 0.615. This is the *apparent* emissivity of the Earth as viewed from space. If the Earth’s atmosphere was *transparent* to IR then the Earth’s emissivity would be that of its *surface*, which is about 0.96. The Earth’s temperature would then be below freezing, which it is not because the Earth’s emissivity is 0.615, not 0.96.

    The reason the emissivity is less than 096 is because the atmosphere is *not* transparent to IR. IR radiation from the surface is blocked by clouds and greenhouse gases which absorb the radiation and re-radiate it. But clouds and the atmosphere are *colder* than the surface (because they are at high altitudes), which means they radiate less energy (even if they are black bodies) than the surface does. For example, a thick cloud at 15000 ft elevation would have an average temperature of about 258K, which means it would radiate (258/288)^4 = 0.64 times as much energy as it would if it were at the surface temperature.

    The “effective” emissivity into space of the surface under this cloud would be lowered from 0.96 (the value for the surface)to 0.64 for the cloud. And the the greenhouse gases throughout the atmosphere absorb radiation and re-radiate it at their lower temperatures. Collectively, the effect of all the greenhouse gases and clouds (at their various heights) is to block most of the surface radiation (emitted with an e of 0.96) and replacing it with their emissions (emitted at a lower emissivity because of their lower temperature) so as to produce an emission that looks like (from space) that it comes from an object with e = 0.615.

    In my simple model I treat low, medium and high cloud as IR-opaque screens blocking and re-radiating surface radiation over the portions of the surface that they cover, on average. I obtain satellite-measured values of emissivity from real clouds to use for my screens and use observed average coverage values.

    The cloudless atmosphere is treated as a translucent “window” (between the opaque screens) having a true emissivity of Ea (which depends on the amount of greenhouse gases in the atmosphere). The effective emissivity of this “window” is the contribution of surface emissions that pass through the atmosphere (its translucent, meaning partially transparent) and the re-radiated emissions from the greenhouse gases at the window temperature Ta (the radiation average temperature of the atmosphere). It all falls out of a simple analysis using only high school algebra.

    So the effect of increased greenhouse gases is to make the atmospheric window a little more opaque. I use Beer’s law to describe the effect of greenhouse absorbers on opacity, which anyone who has had college chemistry might remember describes how colored (opaque) solutes make a solution progressively more colored (opaque) as their concentration rises.

    The model *is* naive, yet works surprisingly well. The key advantage of the approach I have taken is not that its mathematically easier than other approaches (its not), but that the model can be described in terms of simple physical concepts like screens and translucent panes of glass. Instead of a greenhouse analogy (which works by preventing convective heat loss) I use the carport analogy which prevents frost by acting as a radiation shield.

    Comments on my model are welcome malexan@sbcglobal.net

    Comment by Mike Alexander — 10 Aug 2007 @ 4:10 PM

  152. Re #142 **Meanwhile, there has been an overwhelming glacial retreat observed in the last decade. The retreat of the Greenland ice sheet has accelerated from 21.33 m (70 ft) per day to 33.5 m (110 ft) per day in the period from 2001 to 2005 (Howat et al. 2006).**
    You are looking at the surface changes. Have you looked at the thickness or total mass of the Greenland ice?

    Comment by Gerald Machnee — 10 Aug 2007 @ 6:00 PM

  153. Gerald Machnee (#152)

    I agree that surface ice cover is not the best way to measure ice sheet retreat. The mass balance (mass balance = accumulation – loss) is a better way to measure the total ice sheet loss. The data taken from the Greenland ice cap by the GRACE satellite program, launched in 2001, has acheived accurate measurements at low spatial resolutions.

    GRACE estimates that Greenland has lost 129 \pm 15 Gt/year from 2002 to 2005

    Comment by ChrisC — 11 Aug 2007 @ 1:51 AM

  154. I was very interested in Gavin’s dialogue with Bob Bergen (#19). Hoping that I didn’t miss a constriction on conceptual arguments, I’ve tried to respond to Gavin’s suggestion for a more widely accessible version of his six easy steps.

    Step 1: When you add energy to a system, it tends to warm up.
    Step 2: A greenhouse works by trapping some of the sun’s energy that comes through the glass.
    Step 3: The Earth’s atmosphere acts as a greenhouse, giving us an average surface temperature of 15oC (59oF).
    Step 4: CO2 and other trace gases contribute substantially to the atmosphere’s greenhouse capability.
    Step 5: The amount of these trace gases in the atmosphere has been increased substantially by human activities. (e.g., CO2 by more than 30% in the last 150yr.)
    Step 6: The increase in these trace gases represents a greenhouse effect of about +1.9ºC (about 62oF), or +13% of the average surface temperature given in step 3.

    Since CO2 and other trace gases are a major factor in why the Earth is now at a viable temperature for us, increasing their concentrations — and hence raising the surface temperature by more than ten percent — can reasonably be considered a significant change with significant potential for impacting the physical and biological systems that depend upon the Earth’s average surface temperature.

    I’d also like to add that I appreciate Steve Horstmeyer’s comments here.

    Comment by Kea Duckenfield — 11 Aug 2007 @ 3:21 PM

  155. The ‘easy’ steps outlined in the post, although suitable for an intelligent, motivated person, would be above the heads of the adult students I have dealt with. They would have been lost by the word ‘flux’ and get no more from equations than I do from Egyptian heiroglyphs.

    My own version is:

    The Earth is warmed by the sun but heat from Earth ‘leaks’ into space.

    Carbon dioxide absorbs some of the heat coming from the surface of the Earth, which increases the air temperature. Over 100 years ago, it was determined that without this effect Earth would be very much cooler. This has been referred to as the greenhouse effect, and CO2 as a greenhouse gas.

    The amount of CO2 in the atmosphere has been monitored for about the last 60 years and has been increasing steadily. As a result, more of the heat leaving Earth has been trapped. Several lines of evidence point to human activity as being the source of this extra CO2.

    There are other things that affect the Earth’s temperature, including water vapour, methane, pollution in the atmosphere, volcanic eruptions, the amount of energy produced by the sun and changes in the Earth’s orbit around the sun.

    Water vapour is also a greenhouse gas but the amount responds very rapidly to changes in the air temperature. An increase in the level of CO2 causes an increase in the amount of water vapour, which increases the temperature, which increases the water vapour . . until the temperature levels off. The effect is that the amount of water vapour depends on the temperature resulting from other factors, rather than the other way round.

    Clouds can either reflect energy coming from the sun or reflect energy leaving Earth (or both), depending on the type of cloud.

    Methane is a very effective greenhouse gas produced by decaying vegetation, cattle and other sources. However, it does not stay in the atmosphere for very long before being broken down (mainly to CO2).

    Other forms of atmospheric pollution and volcanic eruptions tend to lower the average air temperature, so the year after the Krakatoa eruption was known as ‘the year without summer’.

    The sun’s output does vary in strength, but all the evidence is that any recent changes have not been enough to cause the recent changes in global temperatures.

    The Earth’s orbit changes gradually in a predictable way and these changes have been linked to the Ice Ages. Currently, these changes should be leading to a gradual cooling of Earth but over a timescale of tens of thousands of years.

    When it was realized that the amount of CO2 in the atmosphere was increasing, predictions were made (in the 1960s if not earlier) that temperatures would rise and indeed that has happened. Computer simulations that try to include all the factors that affect the Earth’s temperature find that the only way to duplicate what has actually taken place is to include the effects of CO2 and that nothing else can explain the current warmer temperatures.

    I realize this is very ‘dumbed down’ but I hope I have not done excessive violence to the situation.

    Comment by Richard Simons — 12 Aug 2007 @ 9:46 AM

  156. Richard,

    Your summary was a very good one, clear, succinct, and to the point. My only quarrel is with

    [[Clouds can either reflect energy coming from the sun or reflect energy leaving Earth (or both), depending on the type of cloud.]]

    Clouds don’t reflect thermal infrared energy at all; they absorb it. Clouds are, in fact, a greenhouse agent. They cool more than they heat because they reflect visual wavelengths (and the near-infrared coming from the sun) so well.

    Comment by Barton Paul Levenson — 13 Aug 2007 @ 7:02 AM

  157. Barton,

    Thanks for your comment. I will modify my argument to correct the information on clouds.

    I think the best way to counter denialists (or skeptics if you prefer) amongst the general public is along the lines of:
    CO2 absorbs thermal energy that would otherwise leave Earth.
    CO2 is increasing in the atmosphere.
    This can be expected to increase Earth’s average temperature unless there is a massive, hitherto unknown negative feedback mechanism or violation of the laws of chemistry and physics.
    What is your suggested mechanism?

    Comment by Richard Simons — 13 Aug 2007 @ 8:11 AM

  158. Re: Levenson. Can it therfore be proven that the countries or areas of countries that have a significant cloud cover for most of the year have not had a ‘greenhouse’ rise in temp if if they had not as much as the global mean, and that countries like australia which have very little permanent cloud cover would then tend to record the most dramatic daytime temperature extremes?.

    Comment by Lawrence Coleman — 13 Aug 2007 @ 8:29 AM

  159. Re: Levenson. based on that thought we have nothing to worry about. The warmer the ocean gets the more cloud formation there will over the face of the globe so that will in it self stabilise world temps and we wont get hotter??

    Comment by Lawrence Coleman — 13 Aug 2007 @ 8:35 AM

  160. This shows just how complex the climate sciences and meterology are. If you take all the negative feedback loops and the value of their impact and weight them against all the positive feedback loops and their relative value of affect you will arrive at either a nett positive or negative value. What is happening now is that due to the warming of the earth and biosphere we are creating more positive feedback loops than negaive ones. ie. The warming of the tundra..releasing millions of tonnes of methane..being quickly converted into many more millions of tonnes of CO2 every month..less ice to reflect sunlight back into space where much of belongs, thus heating the polar oceans. The one variable scientists are not sure or can agree upon is the value of importance they can place on each feedback system..they do not understand each in enough detail and how each affects every other feedback system in turn.

    Comment by Lawrence Coleman — 13 Aug 2007 @ 8:48 AM

  161. Re 156. Barton, can you explain a bit more why clouds don’t reflect? They fulfill all the physics requirements for reflection e.g. they contain (mostly) water, a dielectric, their particle size is good for scattering, rather similar to reflection, light is retroreflected by water droplets. True enough it isn’t a case of “mirror mirror on the wall” but it doesn’t have to be specular to qualify as reflection.

    Comment by Dermod O'Reilly — 13 Aug 2007 @ 11:36 AM

  162. re #9, etc: I was never sure where the 5.35 came from. But you deduce that it comes from the answer that it is supposed to generate! That makes no sense.

    Comment by Rod B — 13 Aug 2007 @ 11:40 AM

  163. Re #86 [Given that Hubbert’s Peak for world oil = 2015 (+/- 5 years, depending on reality level of OPEC numbers), it seems unlikely that the amount of air travel is going to keep going up for very long. If it does, it means somebody will be converting a lot of coal to kerosene, not A Good Thing for The Climate. Note that petroleum (down) may not be a good thing if it means (unsequestered) coal (up).]

    I don’t get the impression that the aviation industry shares your belief about the future growth of air travel; nor that the nearness of Peak Oil is generally accepted. I certainly don’t see this as a reason not to campaign against airport expansion (airport capacity seems to be the main constraint on the expansion of air travel, at least in the UK). The more the aviation industry grows, the harder it will be to resist the pressure to make kerosene from coal in order to keep that expansion going if Peak Oil does happen in the near future.

    Comment by Nick Gotts — 13 Aug 2007 @ 1:02 PM

  164. Given the state of world fossil fuels – I doubt there is another 50 yrs of supply left to burn (at current usage) and our ability to consume the leftovers may be even less.

    I like the bacteria analogy, we grow and consume all available resources as rapidly as possible, overshoot and then die off. So far no previous human civilisation has avoided this fate.

    In more recent times, the dot-com bubble showed me that people will stare disaster in the face and fail to see it coming. Sadly I think this shows a continuation of the trend (head, sand, buried)

    Maybe this is actually good news for planet Earth afterall?

    Comment by Darran P — 14 Aug 2007 @ 2:12 AM

  165. [[Re: Levenson. based on that thought we have nothing to worry about. The warmer the ocean gets the more cloud formation there will over the face of the globe so that will in it self stabilise world temps and we wont get hotter??]]

    Richard Lindzen actually proposed such a mechanism in the peer-reviewed literature; he referres to it as an “iris” mediated by tropical cloud-cover. Later satellite observation showed the relation he described was too weak to matter (i.e., not statistically significant). The relationship between world temperature and world cloud cover is still unclear, I believe.

    Comment by Barton Paul Levenson — 14 Aug 2007 @ 7:24 AM

  166. [[Re 156. Barton, can you explain a bit more why clouds don’t reflect? They fulfill all the physics requirements for reflection e.g. they contain (mostly) water, a dielectric, their particle size is good for scattering, rather similar to reflection, light is retroreflected by water droplets. True enough it isn’t a case of “mirror mirror on the wall” but it doesn’t have to be specular to qualify as reflection.]]

    I’m not sure what the reason is that scattering can be neglected for the thermal IR; if I had to guess I’d say it had something to do with the long wavelengths not being susceptible to Mie scattering. But I don’t really know.

    Comment by Barton Paul Levenson — 14 Aug 2007 @ 7:26 AM

  167. RE #88 and Currently “average” is based on the 30 year period 1971 – 2000 and next it will be based on the 1981 – 2010 thirty year period.

    So the average (when weathermen say, “it’s below average”) is a sliding average….and I assume the averages for 1981-2010 may be on the whole a bit higher than the averages for 1971-2000 due to global warming. It will be a bit misleading to viewers who don’t realize it is a sliding (upward) average.

    Comment by Lynn Vincentnathan — 14 Aug 2007 @ 6:41 PM

  168. Re: explaining CO2 warming
    When explaining the increase in the greenhouse effect, I like to use the analogy that the natural effect traps heat like a coat, which has a zipper that allows some of the heat to escape (the “atmospheric window”). When the CO2 in the atmosphere increases, it is like closing the zipper, thereby trapping more heat and we get warmer.

    Great topics, great posts, great site. I think I’ve learned more in the past 2 hours reading this site than in the last 6 months >grin

    Comment by Daniel Pedersen — 14 Aug 2007 @ 10:19 PM

  169. Konstantin (reply 6) wonders what he can say to people who simply don’t seem to care what happens to anyone or anything outside their own sphere:
    1) You can’t safely assume that your part of the world will manage. No one knows that.
    2) Imagine the consequences of the world blaming you/us for deliberately abandoning them to catastrophe. What happens to you when hundreds of millions hate you and have nothing to lose?
    3)”Was grandpa one of the bad people who didn’t care?”

    Comment by B Jackson — 15 Aug 2007 @ 2:07 AM

  170. #157 Richard,

    Very good summary. I’ve been giving talks in Northern California that have followed essentially the same logical pathway. People have been getting it and really appreciate me leaving the too-technical bits out.

    As for your question to the denialists (“What is your suggested mechanism?”) I think it’s important for everyone’s sanity to insert an important step before engaging with them. The step is to check whether you are speaking with someone who has a genuine commitment to understand the situation. If the commitment is there, go ahead and have the conversation. If it isn’t, don’t bother.

    When a person has made up their mind, they will do one of two things with evidence to the contrary a) they will adjust it so that it fits their world view or b) they will reject it completely as absurd.

    It’s an easy human mechanism to watch and understand…I do it with my wife sometimes when we have arguments. If I can catch myself in the moment, I will realize that I’m just arguing to be right. If I don’t catch myself in time, then I often (but not always, sigh) take responsibility for that and apologize.

    Bottom line: if you’re dealing with someone who has made up their mind (like the people who believe the Earth was created 6000 years ago), arguing is pointless — and you’ll just feed your need to be right. (Which is what causes arguments in the first place. Authentic inquiries are a different matter.)

    Comment by Andre Angelantoni — 15 Aug 2007 @ 9:58 AM

  171. (formerly just “Pat”) – my apologies if somewhere above this has been asked, but I was thinking, since (outside sea level rise) it is the regional climate effects and some other specific ones (implications of a rising tropopause) where the ecosystems and economies will really ‘feel the heat’, it might be helpful if there were also “6 easy steps” (I realize it might be more like 60+ and they wouldn’t all be easy) for explaining why we should expect whatever such effects would be expected. Some are relatively easy to explain – why the lower troposphere and surface warm most at the poles (ice albedo feedback) in winter (water releasing summer heat before freezing, whereas the unfrozen water in summer absorbs more solar radiation but does not increase much in temperature) while in the tropics the greatest warming would be in the mid to upper troposphere (in one phrase, temperature dependence of moist adiabatic lapse rate), and of course increased water vapor allowing more intense precipitation, but others are trickier – for example, I haven’t figured out what to expect from the effect of the pattern just described on baroclinic instability and extratropical cyclone life cycle and motion – because it suggests increasing temperature gradients in the upper troposphere but decreasing temperature gradients near the surface; I can speculate but I won’t know if I’m right or not. I could speculate that increased moisture causes a greater role in latent heating for extratopical storms, that an increase in the dry static stability would favor development of horizontally larger anticyclones (dry) (because there is a short-wave cuttoff for growth and it depends on vertical stratification among other things) but not larger cyclones (because of the latent heating), and that the latent heating favors narrower more intense upward movement relative to the downward movement; thus I’m guessing horizontally larger anticyclones and more intense cyclones, although the increased depth of the troposphere should favor larger systems overall (although poleward shifts in storm tracks should reduce these effects, and also favor smaller systems due to increased coriolis parameter f, but perhaps allow larger systems to grow as beta (df/dy) also decreases? – also, I would expect a poleward retreat of extratropical storms based on reduced temperature gradient at lower levels (and therefore poleward shift of subtropical dry zones), but what of the effect of the upper level gradient?), and for that matter, Also, while the moist adiabatic lapse rate decreases with increasing temperature, the total difference in temperature from top to bottom still increases as the tropospheric depth increases, so that the efficiency of the ‘heat engine’ aspect of thunderstorms and hurricanes would increase – for the same amount of heat energy carried upward, a greater portion is converted to kinetic energy … and would that lead to larger hail? (and would greater moisture overall allow for greater contrast of moist and dry air, allowing for stronger supercell storms via more intense evaporative cooling where dry air impinges on the cloud, etc.?) Of course, some fraction of that energy propogates away as gravity waves, and if that fraction changes… And then, for a given speed of westerlies, there is a wavelength of planetary wave that can remain stationary and thus be excited by longitudinal variations in topography and temperature (land-ocean contrasts, ocean currents), so is there a significant effect from changing westerlies (and regional temperature contrasts) affecting wavelengths of stationary planetary waves? What exactly does happen to the Hadley cells – I’m imagining greater latent heating tending to make them stronger overall, greater direct change in greenhouse forcing in the subtropics (due to relative lack of clouds and moisture) tending to weaken them (although allowing poleward expansion), and might poleward expansion allow for greater seasonal motion of the ITCZ? And what happens to anticyclone tracks and blocking anticyclones, … and that doesn’t even include ocean currents … well, that sort of thing is what I’ve been wondering lately. I might yet find it in the IPCC AR4 WGI but I’m not sure. (PS nice job on these “6 easy steps”)

    Comment by Patrick 027 — 15 Aug 2007 @ 8:22 PM

  172. … well, another way of looking at some of the above: I’ve ready mid-latitude storms would shift poleward, be fewer in number, but with more intense storms (I had previously misinterpreted something to mean larger horizontally when it may have meant larger central pressure drop) – is the reason for more intensity, despite decreased lower level thermal gradient, compensation by the upper level gradient, greater latent heating, or both, or neither? And is the reason for fewer storms due just to the storm tracks becoming crammed into a smaller area – (at higher latitudes), to the lower level temperature gradient reduction (in the background mean state, I mean), or to both, or something else? – actually, that brings up another point – if there were fewer storms in a smaller area, there could be the same number per unit area within the given area, but what if they lasted longer (yes/no?) – then storm per unit area per unit time could increase … and while the average thermal gradient at lower levels would decrease (in the zonal average, I mean), there could be longitudinal variations in that, but also temporal variations – one could imagine a moving region in which the thermal gradient is the same but the north-south distance across it is smaller, and the motion of this region would just average out to having a reduced average thermal gradient (and then I automatically think of implication for the vertical wind shear and baroclinic dynamics) …

    Comment by Patrick 027 — 15 Aug 2007 @ 8:48 PM

  173. … in addition to the latent heating synchronized with midlatitude eddy circulations, there are other circulation-synchronized diabatic processes that could weaken or strengthen those circulations – advection-induced thermal anomalies should tend to decay via radiative heating/cooling; cloud and moisture anomalies create variations also create radiative heating/cooling anomalies. I think that the generalized increase in the greenhouse effect should decrease the rate of radiative heating/cooling of thermal anomalies, which would slow energy loss from the eddies – in the lower troposphere, anyway – in the stratosphere, I would guess the opposite could be the case (I don’t know much about the associated stratospheric structure of extratropical circulations except that in the average state, meridional thermal gradient and thus vertical wind shear are reversed, except in winter in some places). For the same cloud and moisture distribution, increased CO2,CH4,etc. should weaken the radiative anomalies, but then again, moisture increases and I expect cloud heights generally would rise, so … (That’s it for now, I’m done.)

    Comment by Patrick 027 — 15 Aug 2007 @ 10:00 PM

  174. Re 166 – (on reflection vs absorption of water droplets) I would guess it’s due to the drop in single scatter albedo as one moves away from the visible band. I’m no expert on Mie scattering but based on geometric optics (not taking into accout the droplet’s surface’s tight curvature’s effect) I would imagine that for each individual scattering, a considerable amount is forward scattering, where the angle change is less than 90 degrees; some of that comes from diffusion around the droplet, some from passage through the droplet – some from glancing reflection near the edge of the droplet’s cross section. Some backscatter from a cloud, especially thicker clouds, would come from successive forward scatterings. As some of that radiation passes through the droplets, it is subjected to absorption within the droplet. (Some backscatter could also be from reflection off the ‘back side’ of the droplet, passing through twice before coming out, so that could also be absorbed within the droplet. Reflection becomes stronger as the rays hit the droplet’s surface (from inside or out) from more glancing angles. With the more complex effects that come into play when a droplet’s size approaches the wavelength of radiation, I don’t know – maybe absorption within the droplet affects radiation reflecting off the surface? (Because I think there is some short distance penetration of the electromagnetic field into the material even if the ray reflects off the surface?)

    Re 162: yes, if you forget 5.35, you can deduce it from the change in radiative forcing per doubling CO2; if you forget the later, you can find it using the former – so it sounds like circular reasoning if taken in isolation, but as I understand it, the logarithmic formula is a useful approximation fitted to the results from more coplex computation where the input would be the known optical properties of CO2 and some other things (probably optical properties of other atmospheric components and the temperature variation with height).

    Comment by Patrick 027 — 16 Aug 2007 @ 6:42 PM

  175. … other thoughts on circulation:

    Actually, for contant optical properties, the radiative decay of thermal anomalies would be weaker for vertically thicker anomalies, which would be the effect in the lower troposphere of reduced lower tropospheric wind shear. As absorptivity increases from increasing CO2 or other greenhouse agents, relatively thicker anomlies to begin with would decay less rapidly then, but for thinner anomalies, the opposite could occur, and the boundary between thick and thin as defined by this behavior would get thinner. … My reasoning for guessing a reverse effect in the stratosphere on thermal anomalies was not because of reversed thermal gradients but because the layers would be optically thinner and more ‘exposed’ to space, etc.

    I wonder if, with reduced wind shear in the lower troposphere, downdrafts in supercells might start more from higher up and perhaps have greater kinetic energy per unit evaporative cooling? But I know the ideal graph of wind velocity with height for supercell development is a lower curved portion and an upper straight portion – and I’m infering that in the future the lower portion becomes less curved and the upper portion becomes more curved… or on the other hand it could be that the lower portion simply gets thicker relative to the upper portion…? – based on generalized zonal mean trends, of course – effects would vary with location and time (and occurence of any given weather phenomenon does the same, so using an average background environment could easily not give the right answer…)

    Comment by Patrick 027 — 16 Aug 2007 @ 7:01 PM

  176. In 174 I meant diffraction where I wrote diffusion.

    Comment by Patrick 027 — 16 Aug 2007 @ 7:54 PM

  177. Re 19: Please, Bob, a more simplified version would be very helpful. Otherwise, I may have to use the analogy (admittedly ill-suited) that if we put an extra jacket on, we should expect to be warmer.

    It would be best if it were a separate topic, rather than being buried among 150+ subsequent postings.

    Comment by Al S. — 17 Aug 2007 @ 2:48 AM

  178. In step 5, you assume that there is one climate sensitivy to radiative forcings indpendent of differences in how those forcings couple to the climate. In particular solar couples to 10s of meters of the ocean while CO2 to a millimeter or so. Hansen’s model based efficacy work, doesn’t reflect this difference in the coupling to the climate, or the different time scales over which these different couplings would impact the climate, so his conclusion that the forcings can be summed is a mere artifact of treating these different forcings unrealistically similarly.

    [Response: Not so. All of the efficacy analyses were done with coupled models that include all of that physics. - gavin]

    Comment by Martin Lewitt — 18 Aug 2007 @ 3:11 AM

  179. Re 174, 175 and 175. I have a lot of difficulty with imprecise terms used in all of these discussions, absorption, reflection, etc., are often used indiscriminately, if the electromagnetic/thermal processes are not used accurately then meaningful discussion becomes impossible. It was Pat’s slip of the pen that caused me to question this whole matter. The greenhouse effect, as frequently described, requires the repeated absorption and re-emission of LW IR in the atmosphere, sometimes illustrated as happening in layers; this is a reasonable model of a diffusion process, more commonly seen in heat conduction, it results in a negative temperature gradient in the direction of heat flow. If this is indeed the right model for the greenhouse effect, well and good but it is not the only heat transfer process in the atmosphere, convection and advection are also important, a balanced assessment needs to be made to show the dominance of radiation diffusion. This radiation diffusion process also occurs in the sun but only below the convection zone. If these two processes are occurring in the earth’s atmosphere then there has to be a good explanation as to how they can live together in the same place because one takes place in the absence of mixing (turbulance?) and the other relies on mixing.

    Comment by Dermod O'Reilly — 18 Aug 2007 @ 6:06 AM

  180. Re 179 – in a nutshell, when air rises it cools as it expands due to the decrease in pressure. When there is no net heating of the air and no mixing of air of different heat contents, the change in temperature follows a dry adiabat (the process is adiabatic, which means it is isentropic , reversable – the exact reverse temperature changes occur in sinking); if the air cools to a point where relative humidity reaches 100 %, then latent heating occurs as water vapor condenses or freezes, and the temperature follows a moist adiabat (also isentropic (sinking would yeild melting, evaporation) only so long as the condensed moisture is not removed from the air (no precipitation), or mixing with air of different heat and moisture content occurs). — if the environmental lapse rate (the rate of temperature decrease with height) is greater then a dry adiabatic lapse rate, then the air mass is unstable and overturning occurs; if the environmental lapse rate is greater than the moist adiabatic lapse rate, then the air mass is stable to localized vertical convection (there can still be large scale overturning due to horizontal temperature gradients, such as a variation of an idealized Hadley cell, though without constant heating and cooling to maintain the gradient, this motion must eventually halt (as would localized vertical overturing without heating below and cooling above) (coriolis effect adds some complexity to large scale overturing, …)). If the environmental lapse rate is between dry and moist adiabatic lapse rates, then the air mass is conditionally unstable – if some air is forced to rise until condensation occurs and then a little bit more, it can become bouant and continue to rise, with potential energy being converted to kinetic energy. An example is what happens in the upward portion of a Hadley cell (Actually, the horizontal convergence actually tends to destabilize the whole lower air mass as well as push air upward). The Hadley cells can be viewed as being driven by latent heating near the equator (with precipitation) and radiative cooling in the subtropics. (why they don’t extend to the poles is because the horizontal temperature gradient in the midlatitudes is strong enough that leads to significant baroclinic instability that generates baroclinic eddies (extratropical cyclones and anticyclones) which convert the potential energy of the background temperature gradient into the potential energy of the gradients associated with the eddies, some of which is converted into eddy kinetic energy by rising warm air and sinking cooler air …(where the sinking and rising are not generally oriented poleward and equatorward from each other, hence the lack of Hadley cell in the average motion (at least that’s how I understand it))… some of which is converted into the kinetic energy of the background state – while heat is transported poleward, etc.) ———- Anyway, the reason the troposphere exists is because pure radiative equilibrium would lead to an unstable lapse rate. Thus there is a convective adjustment; the troposphere, I think on average, tends to be maintained near a moist adiabat by moist convection. The temperature still falls with height (in most parts – there can be low level inversions with negative lapse rates, typically in polar regions and cold winter areas and sometimes at night if the air is dry and clear); so the radiation emitted upward by the troposphere is still less than the radiation emitted downward by the troposphere to the surface. Heat transported upward by convection from the surface through the troposphere must ultimately be balanced by radiative cooling; as the radiative cooling is distributed in some way and not concentrated at the surface, the radiation is emitted at a cooler temperature then it would have been if it had been emitted from the surface, bypassing convection…

    Comment by Patrick 027 — 18 Aug 2007 @ 8:28 PM

  181. well, actually – “(Actually, the horizontal convergence actually tends to destabilize the whole lower air mass as well as push air upward). ” horizontal convergence by itself cannot completely destabilize a layer but it does reduce the stability.

    - also, the moist adiabatic lapse rate is a function of temperature because at 100 % relative humidity, water vapor partial pressure (and thus mixing ratio at a given total pressure) increases roughly exponentially with increasing temperature; at high temperatures, at saturation, more water vapor must condense per unit drop in temperature. There is greater latent heating per unit height increase at higher temperatures, so moist adiabatic lapse rates are slower at higher temperatures. In very cold air, such as found near the top of the troposphere, there is not much moisture even at 100% relative humidity, and the moist adiabats become similar to the dry adiabats. Global warming tends to decrease the lapse rate of the lower troposphere in the tropics, which is why surface warming in the tropics is less than in the mid-to-upper troposphere (but I think the temperature difference from surface to tropopause may yet increase – the tropopause generally should rise as the troposphere warms while the stratosphere tends to cool). In polar regions, warming tends to be greatest near the surface – I think part of that is because polar regions tend to have more stable air to begin with.

    Comment by Patrick 027 — 18 Aug 2007 @ 8:57 PM

  182. In step 2 you say “The fact that different absorbers contribute to the net LW absorption is clear from IR spectra taken from space which show characteristic gaps associated with water vapour, CO2, CH4, O3 etc”.

    But isn’t such IR spectra, in reality, atmospheric emission spectra and not absorption spectra ?

    Which gases at which altitudes contributes radiation to the various lines, and in what proportion to each other ?
    What’s the proportion of re-radiation versus radiation from thermalization for each gas at each altitude ?

    Comment by Chris Bering — 19 Aug 2007 @ 3:00 PM

  183. In response to post 190, the simple model I have developed makes use of the lapse rate in the atmosphere as it is. Most people know that as you climb in elevation it gets colder. Thus, *anything* “up there” that absorbs IR radiation emitted by the surface is going to radiate less than the surface does because it is colder. One might ask how can atmospheric radiation absorbers absorb more energy than they radiate out into space and not warm up? Rather that describing why this is so, simply ignore it. I compare these absorbers to a radiation shield like a carport or the sheets you put in your tomatoes to prevent frost damage. Higher elevations are simply colder. Stuff in the atmosphere than absorbs IR is going to be colder than the surface, on average and so will radiate less energy than the surface will even it they are blackbodies.

    Unless, the atmosphere is *transparent* to IR, surface emissions will be absorbed and reradiated at lower temperatures. And that explains greenhouse warming.

    Comment by Mike Alexander — 19 Aug 2007 @ 8:08 PM

  184. Re 182. – consider any material with some degree of opacity – how far into it can you see? opacity can be measured in terms of optical depth. Using optical depth as the distance coordinate along which a unidirectional beam of radiation travels, the intensity of that beam (of the original photons in the beam) decays exponentially, by a factor of e per unit optical depth – Intensity = inital Intensity * exp(-optical depth). It turns out that the source of a beam coming out of a material is distributed in the same way – that is, if you look along a path, you see more of what’s in front and less of what’s in back, with the distribution of what you see decaying exponentially going away from you. Now, if we’re talking about thermally emitted radiation, then if the temperature changes through a material, parts will look hotter (brighter) or colder (dimmer). If the cold part is in front, it blocks out some of the hotter part, replacing some brighter radiation with a smaller amount of it’s own dim radiation.

    One way to picture this is with a temperature independent factor – let’s call it W. (PS this is the first time I’ve introduced W to explain this concept.) W is the fraction of visual space from some recieving/veiwing location that can be assigned to a radiation source; the total for W at a given location is always 1; contributions to W are distributed along a path where W per unit optical depth decays exponentially with optical depth away from the viewing point. Translated into another coordinate x such as actual distance (or another coordinate – pressure is an especially handy vertical coordinate in atmospheric science (it simplifies some equations to use pressure instead of geometric height)), if the optical depth per unit x is higher, then the exponential decay of W over x is faster, so that less of W is from far away but at the same time the concentration of W at closer positions is increased. So with the atmosphere, for example, if the optical depth per unit vertical distance x increases, you see more from space of the upper atmosphere and less of the lower atmosphere and surface (PS whatever portion of W which is not in the atmosphere must be at the surface). – unless the optical depth of the atmosphere is small to begin with, in which case, less of the surface is seen from space but the entire atmosphere can be seen better. Conversely, if the atmosphere is very opaque, then what acts as the ‘upper atmosphere’ in the previous statement becomes a much thinner layer.

    Anyway, the intensity (power per unit area per unit solid angle, and that per unit wavelength if it is spectral intensity) seen from along a path is the sum of the products of contributions to W multiplied by a corresponding value, which, if scattering is negligible, is the blackbody radiation intensity Ibb for the temperature at that location (if scattering is not neglible, then it is Ibb*a + Isc*(1-a), where a / (1-a) = emission cross section per unit scattering cross section, Isc is scattered light intensity per unit scattering cross section, although that only works with isotropic scattering – scattering is actually quite complicated – luckilly scattering is a small factor in LW (long wave) radiation, the radiation emitted at Earthly temperatures and involved in the greenhouse effect.)

    Then one has to integrate over angles and then over wavelength to get the total effect, but basically, greenhouse gasses and clouds emit and absorb LW radiation, emission being temperature dependent and increasing with increasing temperature (in a somewhat complex way if taken at particular wavelengths), so in the LW range, at wavelengths where the atmosphere is more opaque, it is do to stronger emissivity and absorptivity, but W will be (even after integration over directions – though it is no longer a simple exponential relationship, but it is qualitatively similar) more concentrated in the upper atmosphere at those wavelengths, so from space, the colder upper troposphere and lower stratosphere are more apparent – they are emitting, but not as much as they are blocking (via absorption) from the warmer layers below. At wavelengths where the atmosphere is less opaque, more of the lower atmosphere and surface (which are warmer) can be seen from space; At a given wavelength, if opacity is lowered, space recieves more LW radiative energy at that wavelength from the Earth and atmosphere. Now, there are some wavelengths where the atmosphere is so opaque that W contributions shift significantly into the warmer upper stratosphere, so that the Earth and atmosphere will appear brighter if opacity is further increased – this does not mean a reverse of the greenhouse effect, however – because the stratosphere is quick to radiatively adjust (emitting more to space, thus cooling off so as to emit less to space)(it is not convectively tied to the thermal inertia of the surface as the troposphere is), and at the tropopause (top of the troposphere), it will still appear colder looking down as opacity increases – if it is still being heated by solar energy at the same rate, it will warm up until it no longer appears colder from above. I’ve glossed over the radiation going in between layers – that is important too – some examples,

    1. a troposphere which emits less upward can also contribute to a cooling stratosphere;

    2. it is the downward emission to the surface that makes an increase in the greenhouse effect tend to reduce the diurnal temperature range;

    3. and, increasing the opacity of the troposphere (when it is already opaque to some amount) tends to slow the net upward radiative energy flux, so the vertical heat transport by convection may concievably increase in response – this effect would be enhanced by the reduction in lapse rate in the tropics in the lower to mid troposphere, reduced in polar regions due to the opposite change in lapse rate (I think), but also, this effect might be altered, partly cancelled or overuled by

    a. the effect of increasing opacity at wavelengths where the troposphere is not so opaque to begin with (that would enhance radiative energy exchange through the troposphere, although it still decreases radiative cooling at the surface) (although where one gas is weak, another may contribute, so if CO2 increases, for example, the increase in optical depth at wavelengths where CO2 is weak may be less, in proportional to optical depth, than it would be where CO2 is stronger, if there is significant contribution by, for example, water vapor)

    b. the increasing temperature (which results in stronger emission overall, and increases net radiation between a warmer and colder body at constant temperature difference, especially at shorter wavelengths in the LW range (at longer wavelengths, not so much)

    c. a change in the distribution of solar radiation absorption (via increased water vapor) (because convection can be thought of as the necessary flow of heat between two mismatched distributions: between the distribution of solar heating through the atmosphere and surface and the distribution of net LW cooling through the atmosphere and surface (including the net cooling from exchange with the surface (a negative contribution, usually) and other parts of the atmosphere, not just to space).

    Comment by Patrick 027 — 19 Aug 2007 @ 9:37 PM

  185. Patrick, in 179 I asked you to consider a diffusion process in comparison with convection. I read 180 & 182 (your reply to 179) carefully and I found them very interest because they increased my understanding of convection mixing, thank you for a nice lesson but you do not comment on absorption and re-emission (diffusion). The problem of the greenhouse proposition is that it relies on absorption/emission occurring, a process that is relatively slow and can only take place in the presence of a temperatute gradient (see 179 or look on line for a mathematical description of heat transfer by a diffusion process). An intuitive response would be to consider it as “heat trapping”, however this trapping is just not going to happen when the alternative heat transport process of convection is available, as you so eloquently describe in 180 & 181. Yes there is a temperature gradient in the atmosphere, the lapse rate but that comes from the pressure gradient, the lapse rate would be there even if there was no CO2 or H2O.

    Comment by Dermod O'Reilly — 20 Aug 2007 @ 2:43 AM

  186. [[What’s the proportion of re-radiation versus radiation from thermalization for each gas at each altitude ?]]

    There really isn’t such a thing as “re-radiation.” Gases radiate because they have emission lines in their spectra and are hotter than at absolute zero. What caused them to heat up in the first place can be anything; the resulting radiation is indistinguishable.

    Comment by Barton Paul Levenson — 20 Aug 2007 @ 11:16 AM

  187. Re 186, I think Cris Bering (182) should have a more comprehensive answer because he refers to thermalization. The simple model of polar gases (or any other kind actually) treats it as vibrating in isolation, in which case the resonance band is narrow. I suspect Chris knows that thermalization is a term used to decribe how the energy of one vibration mode becomes shared among all the available modes; this sharing is provoked by collisions for example, if the pressure is sufficiently high. Things do not stop there of course, in the case of trace gases most of this acquired energy is transferred to the non-polar gases where it joins the much larger amounts of heat deposited in the atmosphere by evaporation of water or convection from warm landscape to name a few.

    Classical thermodynamics addresses this situation (proportion of re-radiation, thermalization etc. etc. (there are a lot of energy exchange mechanisms!)) by the copout “it depends on the probability of an event taking place”. But do not give up, further explanation will be found under the titles “Statistical Thermodynamics” and “Statistical Mechanics”. The first and most important conclusion you will draw from studying these thermodynamics of any sort is that, in questions of energy (heat) transfer, no process can be considered in isolation; thus, although statements that refer to “radiative heat balance” can be applied to the solar system where there are only radiative effects, it is utterly unscientific to apply it to the workings a planetary system having a wet atmosphere where evaporation etc. playng a dominant role.

    Frequently proponents of the greenhouse effect cite Arhenius as the founder of their science, I have not found in his calculations any reference to CO2 radiating to outer space or of it coupling heat to other molecules. Basically he appears to assume that CO2 only reflects infrared back to the earth’s surface. Similarly Angstrom sent infrared down a tube; I do not think that this simulates a planetary atmosphere to any useful extent!

    Comment by Dermod O'Reilly — 20 Aug 2007 @ 2:09 PM

  188. Gavin,

    > “The logarithmic form comes from the fact that some particular lines
    > are already saturated and that the increase in forcing depends on the
    > ‘wings’ (see this post for more details).

    Are you sure that the spectral line shape is really needed to explain
    the logarithmic behaviour? If so, then my favored “explanation for dummies”
    is an oversimplification. It goes like this:

    Heat transport outward from the Earth goes by two mechanisms: radiative from
    the Earth surface, and convective + radiative from the tropopause. Looking at
    the IR opacity curve of CO2, one sees that the atmosphere (at sea level
    densities) is opaque for about 20% of the surface area of the Planck curve.
    This means that 80% of radiative cooling comes directly from the surface,
    and 20% from higher up, the tropopause, after convective transport.

    But… the tropopause is at a temperature 50 degrees C less than the Earth
    surface (as your friendly captain will tell you when flying at that level),
    meaning it is only half as effective an IR radiator as the ground. Thus,
    more realistic percentages are 90% / 10%.

    Then, we double the CO2 concentration. As a result, the tropopause (level
    where the air becomes mostly transparent to thermal IR in the wavelength band
    considered) moves up by one scale height, or 5 km. The adiabatic lapse
    rate under it in the troposphere is some 5 degs C per km, meaning that
    the radiative surface cools by 25 degrees.

    This cuts the emissivity from 10% of the total to more like 7%, requiring
    for balance the average global tempature to go up by one-quarter of 3%
    (Stefan-Bolzmann) i.e., 0.75%, or 0.0075 * 272 degs C = 2 degs C. Pretty
    close to the correct value. (But of course we haven’t talked H2O yet ;-)

    This description makes the logarithmic behaviour intuitively obvious: every
    _percentage_ increase of CO2 produces the same _absolute_ uplift of the
    tropopause, the same absolute temperature drop in tropopausal temperature,
    and the same absolute increase in global temperature to compensate.

    And didn’t already Arrhenius derive the logarithmic formula, without knowing
    a lot about spectral line shapes? What did I miss?

    Comment by Martin Vermeer — 20 Aug 2007 @ 2:55 PM

  189. Re 185 – if the temperature profile of the atmosphere is held steady as LW opacity increases, then, as described above, LW emission to space, and in particular the net upward LW radiation at the tropopause, will decrease. Convective transport can and will change in response to changing radiative transport within the surface-atmosphere system (although even some slight temperature changes would be required for that); however, this cannot change the initial change in net LW radiation at the tropopause or net LW radiation to space (setting aside cloud feedbacks, other feedbacks) – which I think can be set aside if the temperatures are held steady); the temperature distribution has to change to reset the LW radiation. That or a decrease in solar heating must occur; until balance is restored, the troposphere will tend to warm up – convection’s role couples the surface temperature and the different layers of the troposphere together, so they warm together, as the tropopause will tend to rise, so that, it could be said, the temperature distribution ‘catches up’ with the distribution of the ability to radiatively cool to the lower stratosphere and to space.

    A simple way to illustrate this is by considering two extremes – an atmosphere completely transparent in the LW range (zero gfeenhouse effect) and an atmosphere of infinite optical depth in the LW range.

    In the first case, all emission to space comes from the surface, there is no convection (at least in a one dimensional column model where horizontal temperature gradients are irrevelant – although even if they did exist I my initial expectation is that there would still be very little convection).

    In the last case, all emission to space comes from the very top of the atmosphere (for the sake of this thought experiment, let’s say there is a top of the atmosphere at some defined location); there is no upper atmosphere any more in the sense of being above the tropopause – the entire atmosphere is tropospheric, and being infinitely opaque, no net upward LW radiative heat flux can occur within the troposphere, hence all heat from wherever solar radiation is initially absorbed must be brought upward to the tropopause entirely by convection, where only then is it radiated to space; thus the surface will be much warmer, and the temperature at the tropopause in this case is the same as the temperature at the surface would be without any greenhouse effect (setting aside horizontal temperature variation for the moment)

    (the above assuming the solar heating is constant – actually, because some solar heating is within the atmosphere, and in particular because some is in the upper atmosphere due mainly to absorption of the shorter wavelengths by ozone and oxygen, this heating would occur within the troposphere in the second case; in the first case it would lead to an entirely thermospheric atmosphere where the atmospheric solar heat gain would be conducted downward (a very slow process requiring a large vertical temperature gradient – a large negative lapse rate) to the surface.

    (this all assumes that no part of the surface (hot in the second case) or atmosphere (hot in the first case) becomes hot enough from solar heating to emit significantly at solar wavelengths (SW radiation)).

    In between these two extremes, both net LW radiation and net convection transport heat generally upward (in polar regions the atmosphere can actually lose heat to the surface even in the daily average) within the troposphere, and net LW radiation transports heat upward within the upper atmosphere above the tropopause (it acts alone in a one-dimensional model meant to be representative of the whole Earth – in three dimensions there is some convection in the stratosphere and mesosphere, but it is not locallized vertical convection, and it is not driven by the potential energy of differential heating as is typical in the troposphere; rather it is driven by kinetic energy coming up from the troposphere)

    Interestingly, in the in between case, because there is significant LW radiational cooling within the troposphere, it is possible for the tropopause (at least parts of it – I’m not sure of the global average off hand) to be colder than the temperature of the surface in the first case or the tropopause in the second case.

    (For variations or more detail on this and previous explanations, See also my comments (not to imply that mine are the best comments or only comments, but I remember my own comments better because I wrote them) at http://climate.weather.com/blog/9_13005.html and http://www.realclimate.org/index.php/archives/2007/04/learning-from-a-simple-model/ (where I was just “Pat”, and also where the topic of molecular collisions and local thermodynamic equilibrium came up – speaking of which:)

    Re 187:

    At local thermodynamic equilibrium (which essentially exists in the vast majority of the atmosphere’s mass because collisions are frequent enough), all suffiently large (for statistics) subgroupings of particles in a given location have the same temperature; so, for example, greenhouse gasses are at the same temperature as non-greenhouse gasses (the same also being true of gasses which absorb solar or other energy – except where fluorescence would occur (could the aurora be described properly as fluorescence?)). Thus, when greenhouse gasses (or other gasses absorbing solar energy) radiate more or less energy then they receive, they cool off or heat up, changing temperature (and/or for water vapor and clouds, potentially changing phase, and/or for oxygen and ozone, chemically reacting); but the amount of temperature change per unit heating or cooling (per unit atmosphere, by one or a few components of that unit of atmosphere) is determined by the heat capacity (per unit atmosphere) of all atmospheric components combined because the gain or loss of heat is distributed by collisions.

    ———-
    PS back to that W thing (which sums to 1 along any one direction) – for integrating over angles (solid angles) to find total W per unit area, for the purpose of illustrating the integration of intensity to find a flux per unit area, (just going downward or upward from that unit area, not both at once), one must weight the W for each direction by the cosine of the angle with the normal to the area (assuming a horizontal area, this is the angle A from vertical – downward, the nadir, upward, the zenith, and then the angle is the zenith angle) and then multiply by the solid angle d(solid angle) (or for numerical integration, a solid angle increment) before integrating over solid angle. For W, the amount per unit area is pi steradians (there are 2 pi steradians in a hemisphere, but the cos(A) factor reduces the integration by half, due to the greater reductions of contributions at higher angles). For finding a radiative flux per unit area F, one finds I (which has units of F per steradian) along each direction as described in comment 184, and then substitute I for W in the above formulation to get F. If F is a function of wavelength and is per unit wavelength, then one must then integrate over wavelength to get the total.
    ———-

    Comment by Patrick 027 — 20 Aug 2007 @ 8:47 PM

  190. Re 189, going backwards through your post. I think your “PS” is for something else. Your “Re 187″ Yes, that is the process for radiative heating of the atmosphere but the atmosphere is mainly heated by the water evaporation cycle, on this point the IPCC quoting Kiehl & Trenberth http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch01.pdf are probably correct (see Fig1 p4/96), but they have one interesting thing in this diagram, the net radiative power from the ground to the atmosphere is only 26W/M2 (390 – 324 – 40) compared with 67W/M2, 24W/M2 and 78W/M2 for absorbed insolation, ground thermals and water cycle, 170W/M2 in total. The IPCC is clearly of the opinion that radiation from the ground plays a very small role in heating the atmosphere and I agree.

    Now to your response, “Re 185″. In your 2nd par. “A simple way” in the first case (no GH gases) there would still be convection since the earth is a globe and the sun heats it according to the cosine law, this gives a temperature gradient along the surface, a one-dimensional model will not show this. However, in the absence of GH gases the atmosphere would still spread heat about as it does now.

    Re “the last case”, LW opaque atmosphere. According to the IPCC the “top of the atmosphere” radiation is 195W/M2 (they have 30W/M2 from clouds) with only 40W/M2 direct from the surface, this situation is not too far from your last case. Thus, on this lovely planet on which we live, the so-called GH gases are responsible for cooling the atmosphere but not for heating it.

    With regard to gases cooling the atmosphere it is useful to consider radiative transfer in a more general way. Radiative transfer is an optical effect from a surface For example, gold coating is used to help define the temperature of satellite parts because of its low emissivity but the emissivity for a mirror finish is much lower than that for a matt finish. The gold surface radiates (or in this case fails to radiate) whatever heat comes from underneath it, the same applies to gassy planets; the top of the earth’s atmosphere radiates heat into deep space from polar gases, it does not matter a damn how the heat gets there, in the case of the earth convection and water cycle are far more powerful heat transfer processes than any possible thermal diffusion.

    So why does the earth’s surface temperature appear to be warmer than radiative equilibrium would dictate? The answer lies with the IPCC’s diagram, the radiative balance does not concern the surface temperature but the temperature somewhere at the top of the troposphere. The surface is, thermally speaking, a long way from the top of the troposphere.

    The surface temperature is governed by the thermal energy in the atmosphere. The second law of thermodynamics states that “entropy tends to maximise”, frequently this is interpreted as “heat flows from hot to cold” and this is true for gases in the absence of gravity. In the presence of gravity a better view is “the energy density (Joules/kg) tends to uniformity”. In this case the temperature throughout the atmosphere can no longer be uniform, it becomes inversely proportional to the pressure (height), it is this that causes the temperature difference between the rocky/watery surface and the radiation zone at the top of the troposphere.

    Have a nice day!

    Comment by Dermod O'Reilly — 21 Aug 2007 @ 11:33 AM

  191. Re #124: Camp and Tung — if the claims that cosmic radiation is important to water droplet nucleation and cloud formation have merit, then the modulation of the cosmic ray flux by the 11 year solar cycle would lead to more cloud cover at solar min (hence colder) and less at solar max (hotter).

    This relative perturbation of albedo would lead to Camp and Tung producing an estimate for forcing that is biased high, would it not? By how much, I wonder?

    Also, the use of “average” temperatures in the discussions concerns me. Since radiation is T^4, and regional (land surface) temperatures range about 10% of T, how is the graininess of the radiation treated?

    Comment by Bryan White — 21 Aug 2007 @ 7:34 PM

  192. Re 190,

    paragraph 2 – I was hesitant about convection without a GH effect because it occured to me that while, from some initial conditions, convection would certainly occur, it might halt or nearly halt as some equilibrium state is reached. As air descends in the polar regions, it would become as warm (or warmer, if precipitation occured during rising in the tropics) as it was when it rose in the tropics (being unable to radiatively cool itself). Actually, I guess that the air would be cooled by contact with the surface at the poles and also by evaporation, so some convection could be sustained – although I expect it would be rather weak (it would only cool one very thin layer of air at a time); if there is any direct solar heating of the atmosphere, as there is now (such as by UV radiation), the lapse rate will be negative (thermals would be inhibited). But solar heating of the atmosphere itself could help contribute to a Hadley cell type circulation – but it would have to be balanced, again, by cooling by contact with the cold regions of the surface, and by evaporation, suggesting it would slow.

    - – - – - -

    paragraph 1:

    Yes, it is true that a majority of vertical convective heat transport from the surface is the latent heat of water vapor – as that water vapor is eventually condensed/frozen and precipitated (sometimes with some intermediate steps re-evaporation, re-condensation, remelting and refreezing), that heat goes into the atmosphere as sensible heat, which, along with sensible heat directly from the surface, can be transported upward even farther.

    In terms of (globally averaged or globally representative) upward vertical heat fluxes (a downward flux is a negative upward flux) (W/m2) as a function of height, the net convective flux at any level is the sum of the net latent heat flux and the net sensible heat flux (except in a very thin layer hugging the surface, where some sensible heat flux is via conduction). The net convective flux declines with height – this is a flux convergence, which means that the atmosphere is being heated (which happens to be balanced by radiative cooling). The net latent heat flux decreasing with height may be partly balanced by a contribution to increasing net sensible heat flux with height; the rest would be balanced by increasing net radiative flux with height. Whether the net sensible heat flux increases or decreases with height would depend on the combination of changes with height in net latent heat flux and net radiative flux; my guess is that the net sensible heat flux grows with height near the surface (if the net latent heat flux declines faster than net radiative flux grows) and declines with height farther up (if the reverse is true at that level). At the tropopause, the net convective flux goes to zero and remains at zero going into the upper atmosphere.

    Upward flux decreasing (increasing) with height => Upward flux convergence (divergence) => heating (cooling)

    The net radiative flux is the sum of the net LW flux and the net SW (solar) flux, the latter being negative as the net SW flux is downward toward SW absorption, a majority of which occurs at the surface.

    The net radiative flux will average to zero above the tropopause if the climate is in equilibrium; this is the sum of a positive LW flux and a negative SW flux. The net radiative flux thus becomes negative in the troposphere to balance the positive convective flux. The SW flux decreases with height (negative with increasing magnitude) from SW absorption in the atmosphere; going down it rises sharply to zero at the surface (well, not quite so sharply in the ocean).

    The net fluxes are the upward minus downward fluxes – for example, there is some downward convective flux as descending air is not at absolute zero temperature and is not devoid of all water vapor; there is some upward SW flux from reflection and scattering. The net LW flux is generally positive because looking up, one sees colder air and space (the higher up one goes, more and more of that is space); looking down, one sees warmer air and an even warmer surface (on average) (the higher up one goes, less and less of that is the surface). Divergence or convergence of the net LW flux is due to an imbalance between LW absorption and LW emission within a layer (which can be further seperated into absorption of upward LW flux, emission downward, emission upward, and absorption of downward LW flux; alternatively one can divide the net LW flux into upward and downward fluxes first, then the divergence or convergence of each of those is related to imbalances in absorption of LW from below and emission upward, and absorption of LW from above and emission downward). That at equilibrium, the divergence of the net LW flux must match the convergence of net SW and net convective fluxes, places a constraint on how the temperature varies with height. An imbalance will tend to heat or cool a layer – above the tropopause, the most direct effect is a temperature change that alters emission of LW radiation, and thus changes the divergence of LW radiation within that layer. Below the tropopause, convection also adjusts. (SW also adjusts if feedbacks affect SW absorption and albedo.) Near the tropopause, there is a potential (depending on the nature of the imbalance) for convection to become important above or to cease being important immediately below, causing movement of the tropopause. Within the troposphere, the potential for convection to occur tends to maintain a lapse rate (a relationship between temperatures at different levels, not directly by itself does it maintain the temperature itself) that will constrain the LW fluxes, and then the convective fluxes will adjust.

    While the net convective flux is larger than the net LW flux at the surface, this does not mean LW fluxes are less important (I’m not saying they’re more important, just that both are important). For example, if the atmosphere were to become colder with no other changes, both convection and the net LW flux at the surface would increase to heat the the atmosphere, as the atmosphere would be radiating less LW flux downward. It would also be radiating less upward; it would still absorb as much from the surface, so there would be less LW radiating to space; except for SW feedbacks, there would thus be an imbalance that tends to heat the system back up. Consider also that the LW flux downward from the atmosphere to the surface is larger than SW heating at the surface – the larger the LW flux downward to the surface, the less relative effect that temporal variations in SW flux to the surface have – so the diurnal temperature range tends to get smaller.

    paragraph 3:

    It is true that greenhouse agents act directly to radiatively cool the atmosphere. But they decrease the LW radiative cooling of the surface, the cooling balances convective heating, they reduce the LW flux to space, in particular from below the tropopause, and thus indirectly make the troposphere warmer than it would otherwise be.

    paragraph 6 – Within the troposphere, convection tends to maintain some lapse rate, because there is a distribution of radiative heating and cooling that tends to make the lower atmosphere unstable to convection. But above the tropopause, this is not so; stable layers exist where the lapse rate is not so great as to allow convection (in a one dimensional model representative of the average – there is some overturning driven by kinetic energy from below.) – There is essentially no a priori limit to how stable the air can be – how strongly negative the lapse rate can become.

    Comment by Patrick 027 — 21 Aug 2007 @ 7:54 PM

  193. - oh, and you have a nice day too!

    Comment by Patrick 027 — 21 Aug 2007 @ 8:09 PM

  194. Re 190 paragraph 2 – So what I’m picturing (for zero greenhouse effect) is an atmosphere with small horizontal temperature gradients at most levels except very near the surface; there would be a very strong but thin (surface-hugging) inversion near the poles that would weaken towards the tropics. Within that layer there would be a tendency for convection. Not much heat would actually be transported owing to the thinness of the layer. The layer might be so thin that friction with the surface would be significant or perhaps dominant? relative to pressure gradient and coriolis forces.

    Comment by Patrick 027 — 21 Aug 2007 @ 8:39 PM

  195. Patrick, have you looked at Ray Pierrehumbert’s website (via the Contributors links, on right side of page)? He has an article on “Science Fiction Atmospheres” that I found helped me understand this.

    Comment by Hank Roberts — 21 Aug 2007 @ 8:47 PM

  196. Re 192your par.6 “Within the troposphere, convection tends to maintain some lapse rate” this gives me problems, the lapse rate derives from the pressure gradient which is due to gravity, ja oder nein? I have seen it said that the lapse arises because the sun heats the surface, if you are of this persuasion then this is not the place to resolve the matter!

    [Response: The lapse rate arises because any larger gradient is unstable to small perturbations. Those perturbations in the atmosphere are associated with convection, since the profile is to a large extent heated from below. - gavin]

    Re 195. I have examined Ray Pierrehumbert’s new (draft) book, it is indeed a formidable work but it gives rise to horrendous problems, he should re-examine his description of the 2nd law of thermodynamics and try to reconcile all the methods of heat transport in the earth’s atmosphere before piling everything on to radiation.

    Comment by Dermod O'Reilly — 22 Aug 2007 @ 2:13 PM

  197. Patrick, stand outside of the planet and look at it whole: radiation _is_ all that’s going in and out. The other forms of heat transport are internal rearrangement.

    Comment by Hank Roberts — 22 Aug 2007 @ 2:27 PM

  198. Thanks Hank. One is the weather and the other is …. oh I am going to bed, the sun went down a few hours ago

    Comment by Dermod O'Reilly — 22 Aug 2007 @ 3:26 PM

  199. The CO2 theory has a major inherent fallacy. Let me start with the summary of the CO2 lag effect by RealClimate:

    “The 4200 years of warming make up about 5/6 of the total warming. So CO2 could have caused the last 5/6 of the warming, but could not have caused the first 1/6 of the warming.”
    (they have edited out a previous statement that CO2 probably caused about 50% of the warming)
    “From studying all the available data (not just ice cores), the probable sequence of events at a termination goes something like this. Some (currently unknown) process causes Antarctica and the surrounding ocean to warm. This process also causes CO2 to start rising, about 800 years later. Then CO2 further warms the whole planet, because of its heat-trapping properties. This leads to even further CO2 release.”

    However the AGW scientists never address the “sequence of events” for a falling temperature. It is implied by CO2 theory that a certain concentration of CO2 will lead to higher temperatures and thus more CO2. The logical conclusion is that we will get runaway heating. But we didn’t . And why we didn’t never is addressed or explored.

    For illustrative purposes let’s label ocean temperature at 0 degrees during the glacial and 20 degrees at the height of the interglacial.(Studies have shown differences of 20 degrees). Being conservative, lets use the claim that CO2 only causes 50% of the interglacial warming. So the sun raises the ocean temperatures to 10 degrees and causes a release of CO2. Then in accordance with RealClimate’s above summary, a feedback mechanism results where the CO2 traps heat which causes additional release of CO2 and thus more heat trapping.

    I assume you would agree with this scenario. So why does the temperature peak and fall? Lets assume the the cycles of the sun’s orbit now wanes causing the temperature to drop back to 10 degrees and accounting for its full 50% of the warming. But at 10 degrees we still have higher concentrations of CO2 than we had a the glacial minimum I labeled 0. And at 10 degrees the CO2 theory says that there is enough CO2 to trap more heat and release more CO2. We are right back to raising the temperature towards the interglacial maximum. Thus my contention that CO2 theory predicts that CO2 will counteract cooling forces and logically we would never return to the 0 degress of the glacial. Then logic dictates that to reach the observed glacial minimums, the climate must be sensitive to something more powerful than CO2.

    Or else you must argue that there are mechanisms that pull CO2 out of the atmosphere and allow the temperatures to fall. However if your argue that processes that store CO2 like
    photosynthesis or oceanic carbonate formation help lower the CO2 and thus the
    temperature, we are left with another question. At any given temperature such CO2 sinks should be active and thus just as likely to prevent the rising temperatures of the approaching
    interglacial as stimulate the falling temperatures of the approaching glacial
    period. We can not argue that at 10 degrees CO2 causes additional warming during an approaching interglacial, but at 10 degrees CO2 is absorbed by sinks to allow cooling. You can not have it both ways, and this is the inherent fallacy of the CO2 model.

    [Response: Rather than 'never [being] addressed or explored’ we addressed the reason why you don’t see a runaway effect here: http://www.realclimate.org/index.php/archives/2006/07/runaway-tipping-points-of-no-return/ and it’s easy to show that the observed T/CO2 regression and the radiative forcing calculations don’t come any where close to providing enough response to ‘runaway’ (which is good). It does work both ways though and your postulated example is flawed (do a simple mathematical model with an external forcing and a CO2 feedback). – gavin]

    Comment by Steele — 22 Aug 2007 @ 3:44 PM

  200. “It does work both ways though and your postulated example is flawed (do a simple mathematical model with an external forcing and a CO2 feedback). – gavin”

    I did just give a very simple mathematical model. Perhaps you could show me how it is flawed vs just saying it is flawed.

    [Response: Sorry, but your example was a flawed thought experiment. Try coding this up with the following equations: c dT/dt = F_ext + 5.3*log(CO2/CO2_orig), dCO2/dt = a*(T-To) with suitable values for a,c, To etc. Then play around with the external forcing F_ext - sinusoidal maybe, and see what happens. If you get it right you'll see T following F_ext with some lag (depending on a and c) and CO2 following along in both the ups and the downs. c is the heat capacity of the system, pick 'a' so that you get the observed glacial-interglacial difference for the peak to trough difference in F_ext. With large 'a' you'll see a runaway affect, but for realistic values you won't. - gavin]

    Comment by Steele — 22 Aug 2007 @ 4:38 PM

  201. Re 199- Steele begins with the words “The CO2 theory has a major inherent fallacy.”

    Categorical assertions like this are not only misleading, but seem silly, unless they come from a top climate scientist. Would you care to provide a link to something that establishes your qualifications to make such a statement? Otherwise, maybe you could tone it down a bit, practicing a little of the humility that marks real science.

    Comment by Ron Taylor — 22 Aug 2007 @ 4:56 PM

  202. Rather than ‘never [being] addressed or explored’ we addressed the reason why you don’t see a runaway effect here: http://www.realclimate.org/index.php/archives/2006/07/runaway-tipping-points-of-no-return/

    Also my apologies for misudnerstanding. My reference to “never addressed or explored” was specifically aimed at your article on CO2 lag effects. In that article you only adressed the portion of the glacial-interglacial cycle that exhibits rising temperatures.

    I now have re-read your article on runaways and tipping points,that I had read over a year ago and forgotten about. To account for the fact that here is no runaway you said, “A simple example leads to a geometric series for instance; i.e. if an initial change to a parameter is D, and the feedback results in an additional rD then the final change will be the sum of D+rD+r2D…etc. ). This series converges if |r|

    [Response: this is cut off because you used a less than symbol, use & l t ; instead... - gavin]

    Comment by J. Steele — 22 Aug 2007 @ 5:01 PM

  203. Re 195 – Thanks, I’ll look at that.

    Comment by Patrick 027 — 22 Aug 2007 @ 9:51 PM

  204. [Response: Sorry, but your example was a flawed thought experiment. Try coding this up with the following equations: c dT/dt = F_ext + 5.3*log(CO2/CO2_orig), dCO2/dt = a*(T-To) with suitable values for a,c, To etc. Then play around with the external forcing F_ext - sinusoidal maybe, and see what happens. If you get it right you’ll see T following F_ext with some lag (depending on a and c) and CO2 following along in both the ups and the downs. c is the heat capacity of the system, pick ‘a’ so that you get the observed glacial-interglacial difference for the peak to trough difference in F_ext. With large ‘a’ you’ll see a runaway affect, but for realistic values you won’t. - gavin]

    Gavin,

    You have ignored my main point. yes, my choice of phrase “runaway warming” was ill-advised and you have properly corrected my statement. I should have more accurately said that CO2’s heat trapping ability will unceasingly push temperatures to some asymptote. And given the lag in changes of CO2, it is logical to expect that once the other external forcing stops, CO2 will push the temperature back towards that asymptote.

    dCO2/dt = a*(T-To)

    This equation assumes an instantaneous change in temperature due to CO2 changes or instantaneous changes in CO2 due to temperature. We know this is not the case as observed by the lag effects. If a given level of CO2 is causing an increased energy input, while external forcings cause a drop in energy input there is a theoretical rate of change at which the two opposing tendencies will offset. The change is not instantaneous. In addition if the external forcing only drops energy input by ½ or 1/5 as you have suggested, then the counteracting forcing of CO2 will prevent temperatures from returning to the glacial minima. Your equations showing instantaneous changes is not flawed just misapplied.

    c dT/dt = F_ext + 5.3*log(CO2/CO2_orig)

    This equation simply states that changes in temperatures are due to a change in all the external forcings plus a function of CO2 concentration as well as being proportional to the estimated heat capacity (will heat capacity be a constant?). No problem. I am just arguing that climate is more sensitive to the external forcings, and must be because observed temperatures drop to glacial minima despite the opposing warming by any given level of CO2.

    [Response: Hmm... thinking about it the CO2 equation isn't right. It should be something like b dCO2/dt = a (T - To) - (CO2 - CO2_orig). That makes (To, CO2_orig) a stable point and all stable CO2 levels must satisfy d(Co2)~a d(T) as is seen in the ice cores (a ~ 20 ppm/ºC ). The factor b provides the delay. Try that. - gavin]

    Comment by Jim Steele — 22 Aug 2007 @ 10:56 PM

  205. CO2 Problem Step 7:
    “All the coal that can be mined safely and inexpensively is gone”

    (From a news item I heard on NPR this morning. I think that’s a pretty good quote, but I might have a word or two wrong. If someone has the transcripts from this morning’s piece on the Utah mine collapse, you could get a better quote.)

    Comment by FurryCatHerder — 23 Aug 2007 @ 6:47 AM

  206. I am a bit confused by your equations.
    Your new equation

    b dCO2/dt = a (T – To) – (CO2 – CO2_orig).

    Again with no external forcing to change temperatures the expression a(T-To) would equal zero. So this equation seems to be saying that b must be negative 1 to maintain the equality but that means a positive increase in CO2 will create a negative change in CO2?

    [Response: You could put in a forcing term if you wanted, but it's a distraction from the ice age story. But yes, if T=To, the CO2 system has a single stable point at CO2_orig. Perturbations in CO2 will be damped without the temperature feedback. That seems appropriate. But why should b=-1? This equation defines the growth rate d(CO2)/dt (i.e. the time differential). If CO2>CO2_orig, than the growth rate will be negative - i.e. it will bring it down to CO2_orig on a time scale define by 'b'. - gavin]

    Comment by J. Steele — 23 Aug 2007 @ 9:35 AM

  207. re: #205 F.C.H.

    [~40 years ago, I did summer jobs at the US Bureau of Mines Pittsburgh Center; my first-ever paper was "A computer program for the stereographic analysis of coal fractures and cleats." I never expected any of that experience to become even slightly relevant again...]

    cActually, it is far safer and inexpensive to do surface mining, like in the big deposits in Wyoming, Montana, etc, than in underground mines, and there is a strong trend towards more of the former and less of the latter.

    Jeff Goodell’s “Big Coal” is useful. So are:
    http://www.cdc.gov/niosh/mining/statistics/images/fuscsm.gif,
    which compares surface and underground
    http://www.cdc.gov/niosh/mining/statistics/pdfs/m_fa.pdf

    The latter has a map of 28 fatalities in coal mining in 2004: most are in the Appalachians.

    http://www.nma.org/statistics/pub_facts_coal.asp has many useful tables; one can compare the growth of Western & surface mining to slow decline of Eastern & deep mines, from 1990 to 2006:
    http://www.nma.org/pdf/c_facts_glance.pdf
    In
    http://www.nma.org/pdf/c_most_requested.pdf one can find that 2006 estimates give “Production Per Miner Per Hour” of:
    3.99 underground
    10.39 surface mines

    So, maybe what they meant on NPR was that all the coal in the Utah mine that an be mined safely and inexpensively is gone, because clearly, the trends are otherwise: it is becoming safer and more efficient to *mine* coal.

    Whether it is safe to *burn* it without CO2 sequestration is another story.

    Comment by John Mashey — 23 Aug 2007 @ 11:12 AM

  208. Re 201 Rod you say “Categorical assertions like this are not only misleading, but seem silly, unless they come from a top climate scientist.”

    I think you have a problem here. How do you choose a “top” scientist of any sort? (whatever that may mean.) The IPCC chooses thousands it would seem, for me most of them are very nice guys, if you look at their websites they are good with children, know how to use a keyboard and they are very condescending about people who are not scientists (what is a scientist?)

    Perhaps you know a top scientist when you see one. Do you think Einstein was a top scientist? If so do you share his views on his pupil Werner Heisenberg’s ideas about uncertainty?

    I have a big problem with anybody who is not up to speed with thermodynamics but all I require is that they get curious about it, I don’t know everything but I sure as hell try to find out.

    Comment by Dermod O'Reilly — 23 Aug 2007 @ 4:21 PM

  209. Every time I discuss AGW the question comes up about temperature leading CO2 increase. Can anyone point me towards information that shows CO2 driving the temperature?

    Comment by Peter Brunson — 23 Aug 2007 @ 5:38 PM

  210. Gavin, in 196 you responded “[The lapse rate arises because any larger gradient is unstable to small perturbations. Those perturbations in the atmosphere are associated with convection, since the profile is to a large extent heated from below. - Gavin]” If you mean the lapse rate does not derive from gravity then you are stuck with the problem of where the pressure gradient comes from. It is basic physics that energy tends to be equally distributed in an unperturbed system e.g. equal pressure and temperature in a pressure vessel.

    The situation on the planets is different from a pressure vessel because of gravity (holding the atmosphere on the planet), the mass of the atmosphere is no longer distributed uniformly but the energy (Joules/kg.) remains uniformly distributed, 1kg. of air (CO2 or anything else) at the tropopause contains just the same energy as 1 kg. at the surface, the difference being that the 1kg. at the t(r)op. has potential energy because it has been raised from the surface (remember zero volume a 0K) to the troposphere, while the 1kg. at the surface has equal potential energy because it is compressed by all the stuff on top of it. This is not immediately obvious because the temperature gradient (lapse rate) might appear to contradict the 2nd law of thermodynamics (why doesn’t the heat at surface flow to the cooler place “up there”). This would be a too simple interpretation; it is the energy that is uniform, not the temperature, the lapse rate is built in with the bricks because of gravity.

    Energy arriving from the sun keeps everything nice and warm, the heat is taken to the top of the atmosphere by adiabatic convection (remember adiabatic, the energy remains constant, pressure, volume and temperature change) takes energy at a high temperature and delivers the same energy to the tropopause at a lower temperature where it is radiates to deep space, courtesy of polar gasses. Here is the sting in the tail, it matters little what the radiating gas is, in the case of Venus it is >90% CO2, if this CO2 were replaced by air the temperature at the surface would be much higher because of the different gamma of the O2/N2 mixture.

    [Response: Of course gravity is important. Who ever said it wasn't? That sets the relationship between the integrated density and pressure. Given that, you can then determine whether a particular temperature profile is stable or not. Gradients shallower than the adiabat are unstable, therefore the adiabat sets the minimum gradient. The greenhouse effect works regardless of the lapse rate as long as there is one. - gavin]

    Comment by Dermod O'Reilly — 24 Aug 2007 @ 2:15 PM

  211. Re 210 (your response) You accept that gravity is important, well do you think it is important enough to explain the 30K difference between the surface temperature and the tropopause? If you don’t accept this then: why is gravity important to you? Your response “Gradients shallower than the adiabat are unstable, therefore the adiabat sets the minimum gradient.” has got nothing to do with this 30K difference; it is in connection with local conditions that determine the weather, morning calm to hurricanes. Of course the local weather changes the lapse rate, but locally; amazingly I happen to know that also. The current argument is, if I am not mistaken, not about the weather but about effects that are averaged over the whole planet. I do not appreciate having the discussion deflected in this way.

    [Response: The difference between the surface and the tropopause is more like 100 K in the tropics. And frankly, I have no idea what point you are trying to make and so any deflection is purely accidental. - gavin]

    Comment by Dermod O'Reilly — 24 Aug 2007 @ 3:30 PM

  212. Re #209: Peter Brunson — This has been the subject of comments and replys on many previous threads. Also, on the sidebar you will find a link to the AIP Dicovery of Global Warming site. The page there on carbon dioxide as a greenhouse gas ought to serve you well.

    Comment by David B. Benson — 24 Aug 2007 @ 4:54 PM

  213. Dermod, what sources are you drawing on for the point you’re trying to make? Perhaps if you give a pointer to your sources it will help understand what you’re trying to get at. I’ve tried your terms and phrases with Google Scholar and not found anything that seems likely, but you seem to be trying to develop a basis for some point.

    Comment by Hank Roberts — 24 Aug 2007 @ 6:25 PM

  214. Re 210 – but it does matter what the compostition is, not just because of the convectively maintained tropospheric lapse rates depending on specific heat and molecular mass as well as latent heating; both SW and LW radiative properties matter. The height of the tropopause is climate-dependent and will be affected by these things. Some net LW radiative energy transfer does take place within and from and to the troposphere on Earth because it does not approach infinite optical depth.

    Comment by Patrick 027 — 24 Aug 2007 @ 9:05 PM

  215. Re 210 – and gravity, yes, the convectively maintained lapse rates depends on gravity, and in general gravity determines the relationship between density and vertical pressure gradient which is just an important feature of the atmosphere. But more stably stratified layers can and do exist as has been mentioned.

    Comment by Patrick 027 — 24 Aug 2007 @ 9:10 PM

  216. [[The situation on the planets is different from a pressure vessel because of gravity (holding the atmosphere on the planet), the mass of the atmosphere is no longer distributed uniformly but the energy (Joules/kg.) remains uniformly distributed, 1kg. of air (CO2 or anything else) at the tropopause contains just the same energy as 1 kg. at the surface]]

    Aren’t you ignoring thermal energy? A kilogram of air at the tropopause is a lot colder than one at the surface, and therefore carries less thermal energy.

    Comment by Barton Paul Levenson — 25 Aug 2007 @ 4:20 PM

  217. Re 216 You are nearly there Barton but the road is a bit rocky. The short answer is that the energy is the same but the volume is bigger, the energy of 1kg. is spread about a lot more (energy/kg. is the same).
    The process is called adiabatic because the heat content of the kg. gas at the bottom surface is the same as the kg. at the top surface; if you are familiar with transformers it is a very similar process, energy is taken at one pressure (voltage; temperature) and delivered at another. When gas is compressed adiabatically work is done on it, it gets hotter; when it expands adiabatically it does work. This is not quite so obscure as it looks because the work compressing the ground level gas corresponds exactly to the work (against gravity) needed to lift the top level kg. to its top level; it may not be obvious but the different kg.s will have different temp. for the same energy.
    This last point is a major pitfall when getting into thermodynamics, tutors always baffle undergrads. at this point by introducing the term “enthalpy” which is a measure of the total energy, it does not alter the explanation, the point remains the same, a mass of gas can have the same energy at two different temperatures.

    I have just noticed an error in my post 210 (patrick remarks on it in 214) it DOES matter what kind the gas is because of the different heat capacities between e.g. CO2 and N2. In thermodynamic terms gas masses are comparable if they have the same number of molecules, in this case they will have masses in proportion to their molecular weights, thermodynamics refers to “mole(s)”, a mole being (to some) the weight (in kg.) of “Na molecules of gas” where Na is Avagadro’s number (approx. 6x 10to23 (big!)) Some use the “gm. mole” instead of the “kg. mole”. The purpose of this is to enable comparisons to be made between different gases.
    YOU ARE NOT finished yet, not all molecules are the same, some are monatomic with 3 degrees of freedom, others diatomic with more degrees of freedom; this gets huge!

    I have gone so far with explanations not because I am a teacher, I am not (I got out of university as fast as I could) but because few contributors seem to consider this whole global warming/CO2 thing as a problem of thermodynamics; it is PURE thermodynamics, like rocket science and lots more. Anybody who thinks that it is just a matter of radiative transfer does not understand the technical content and will have a hard job recognizing the real answer when they see it. I am strongly of the impression that the whole group of IPCC experts does not contain anyone who is informed about thermodynamics because they are not using the right words. It isn’t because I am good at thermodynamics, I’m not, it is just that, when I see the words I know where I have to start looking.

    Just to finish, I am not saying that CO2 doesn’t heat the atmosphere , it does, it also cools it, the net effect is zero.

    Patrick re #215, I hope you refer to “stably stratified layers can and do exist as has been mentioned” you mean troposphere, stratosphere etc. otherwise I do not understand you. The troposphere , apart from local inversion etc. (e.g. weather processes), does not have layers on a global basis, the apparent layers of clouds all derive from lapse rate but not the global lapse rate due to the mass of the atmosphere.

    Comment by Dermod O'Reilly — 26 Aug 2007 @ 9:59 AM

  218. Re 217 – actually the entirety of the energy content is a bit tricky – work is done to lift a kg of air up, but the air does work on it’s environment by expanding at nonzero pressure as the pressure drops – this is where the cooling comes from. The work done to lift the air is related to work done by the surrounding air which sinks around the rising air, and if that air at a given pressure level is more dense than the rising air as it passes through that same level, then more work is done by the sinking air than is done on the rising air; thus there is a net decrease in gravitational potential energy as it is converted into kinetic energy in convection (or in the reverse case, kinetic energy is converted into gravitational potential energy).

    Also, there are a few different ways one may refer to layers in the atmosphere. Well-defined layers (defined by characteristics that would be lost by mixing and would take awhile to be restored) may tend to exist or be more likely to persist when and where the air is more stable, where there is reduced vertical mixing.

    There are other layers that may be defined by different characteristics – the troposphere is defined by weaker stratification. Within the troposphere, there is an atmospheric boundary layer defined by the mechanical and sometimes thermal effects of contact with the surface. There may be other layers which have dry adiabatic lapse rates within them and therefore can be expected to be well-mixed layers. There can be a layer of persistent low clouds over some parts of the ocean. There are the ionosphere and magnetosphere, defined by electric and magnetic characteristics; there are the homosphere and the heterosphere, defined by the relative importance of eddy diffusion (which, dominating in the homosphere, tends to evenly distribute the gasses which are not rapidly added to or removed from the atmosphere, or otherwise rapidly undergoing chemical or physical reactions (such as ozone and water vapor)) over molecular diffusion (which, in the heterosphere, above the turbopause, where molecular collision frequencies are quite low, allows gasses of greater molecular mass to settle out – mathematically, it is as if each component forms it’s own seperate atmosphere, with it’s own rate of roughly exponential decrease of partial pressure with height (variations due to changes in temperature or some net upward or downward diffusion rates feeding chemical reactions, etc.); thus there is a region where atomic oxygen is the most abundant component).

    But more generally, one may speak of layers of atmosphere in the sense that each step (such as those one would use in numerical modelling) in a vertical coordinate, like geometric height, gravitational potential energy, pressure, or potential temperature, can define a layer of atmosphere. I may have refered to these arbitrary layers when discussing radiation exchange among layers of air or between them and the surface or space.

    ————
    PS in the discussion of net radiation fluxes – either SW or LW – each can be subdivided by contributions from different wavelengths, and there can be interesting variations, for example, in LW fluxes, the total net flux upward is always positive, at least for the global average, although this is probably the usual case even locally (one exception could be within a low level inversion capped by clouds). But the net LW flux at wavelengths where the atmosphere is very opaque (perhaps at a narrow peak in CO2 opacity around 15 microns), if it is opaque enough, might actually be downward in the middle of the stratosphere – because looking up one would mainly see the warm upper stratosphere and lower mesosphere, while looking down one would mainly see the cold lower stratosphere and top of the troposphere. But at other wavelengths, the net LW flux is upward throughout the stratopshere, because one can see farther, to the cold upper mesopshere and space, and to the warmer mid-troposphere (unless clouds get in the way), or maybe even the lower troposphere, and even some of the surface (unless high-humidity air masses get in the way).
    ————

    The net effect of additional CO2 is to raise the temperature of the surface and troposphere and cool the stratosphere.

    Which words are the IPCC experts not using that you think they ought to? (I really think at least some of them do understand thermodynamics – at least as well as they need to for climatological applications.)

    Comment by Patrick 027 — 26 Aug 2007 @ 6:23 PM

  219. > I am not saying that CO2 doesn’t heat the atmosphere , it does, it also cools it, the net effect is zero.

    That’s exactly what happens, and while the CO2 level is stable, so is the net effect.
    Add CO2, and with the various lag times involved, the planet warms over a period of some centuries.
    The net effect is again zero when the planet returns to radiative equilibrium.

    Comment by Hank Roberts — 26 Aug 2007 @ 7:37 PM

  220. Dermod,
    I’m afraid we are having trouble understanding what point you are trying to make. Could you please state your thesis simply and succinctly?

    Comment by ray ladbury — 26 Aug 2007 @ 9:21 PM

  221. Re #220. Surface temperature (288K) is determined by (global average) lapse rate and effective radiation temperature of the Earth. These two temperatures are a function of the adiabatic compression of the atmosphere by gravity; the size of the compression is determined by the atmospheric mass and the planet’s gravity (this is why Venus has 460C surface temp.). Incoming absorbed radiation becomes outgoing long wave radiation that is, in turn, sourced by the surface, H2O gas and CO2; reflected radiation is per albedo. Radiative transfer to the atmosphere is very small compared to evaporation and convection.

    Models used by IPCC etc. that rely on “blocking” or “trapping” of infrared are known to occur e.g. the radiation zone in the sun. This “blocking” or “trapping” is in fact diffusion processes similar to conduction (of heat). Diffusion processes are very slow and are not applicable to the physical reality of the Earth and Venus; they cannot co-exist with the dominant (much faster) convection process (the Sun has a convection zone also).

    I hope I have not lost anything in this (adiabatic) summary!

    Comment by Dermod O'Reilly — 27 Aug 2007 @ 7:07 AM

  222. Re #220 & #221 I did miss something. The adiabatic lapse rate accounts for the 33K difference between the mean surface temp. (288K) and the effective radiation temp.(255K).

    Comment by Dermod O'Reilly — 27 Aug 2007 @ 7:28 AM

  223. Dermod,
    I mostly agree with your summary, but the fact that convection, latent heat, etc. decrease in importance the further one gets from Earth’s surface is also important. In the tropopause and stratosphere, radiation is the dominant transport mechanism for outgoing radiation. Details of absorption and the balance between re-radiation and other relaxation processes do become important here in quantifying the magnitude of the greenhouse contribution and especially the changes in that contribution due to increasing ghg concentrations.

    Comment by Ray Ladbury — 27 Aug 2007 @ 7:43 AM

  224. Re #223 ” In the tropopause and stratosphere, radiation is the dominant transport mechanism for outgoing radiation.(YES) Details of absorption and the balance between re-radiation (don’t understand) and other relaxation processes do become important here in quantifying the magnitude of the greenhouse contribution.”

    I don’t think that the tropopause is where the greenhouse effect is supposed to take place, the density is far too low; that is why thermal processes such as convection cease. With even more certainty there are no diffusion processes to be found in the tropopause such as the absorption/emission process that characterises the greenhouse hypothesis. May I ask someone to explain just how the greenhouse process causes a temperature gradient? For me the perfectly good gradient due to the adiabatic lapse rate is quite sufficient, it is out there to see on the top of the mountains, why is another one needed?

    Comment by Dermod O'Reilly — 27 Aug 2007 @ 8:09 AM

  225. > just how the greenhouse process causes a temperature gradient?

    Incoming sunlight warms the planet; outgoing radiation at the top of the atmosphere from CO2 cools the planet.
    Add CO2 rapidly, faster than biogeochemical cycling removes it.
    Heat is delayed leaving the planet, while incoming sunlight continues at its usual rate.
    The lower atmosphere warms.
    The warmer atmosphere expands.
    The expanding atmosphere lifts the top of the atmosphere higher.
    When lifted higher, gas expands and becomes cooler.
    The upper atmosphere is where CO2 emits infrared that has a good chance of leaving the planet.
    The upper atmosphere has been cooled by being lifted, so it’s emitting lower energy cooler infrared.
    Since the outgoing infrared is less effective in removing heat, the planet continues to warm.
    Eventually the warming of the atmosphere extends to the top, and energy balances again, after some centuries.

    Comment by Hank Roberts — 27 Aug 2007 @ 9:12 AM

  226. [[Re 216 You are nearly there Barton but the road is a bit rocky. The short answer is that the energy is the same but the volume is bigger, the energy of 1kg. is spread about a lot more (energy/kg. is the same).
    The process is called adiabatic because the heat content of the kg. gas at the bottom surface is the same as the kg. at the top surface
    ]]

    That would be true only if the entire thermal structure of the atmosphere were due to convection. It isn’t, there are also radiative effects. The thermal energy per kilogram is NOT the same at ground level and at the tropopause.

    Comment by Barton Paul Levenson — 27 Aug 2007 @ 9:54 AM

  227. [[I am not saying that CO2 doesn’t heat the atmosphere , it does, it also cools it, the net effect is zero.]]

    Completely wrong. You’re arguing against the greenhouse effect here, which is well established physics.

    Comment by Barton Paul Levenson — 27 Aug 2007 @ 9:55 AM

  228. [[Re #220. Surface temperature (288K) is determined by (global average) lapse rate and effective radiation temperature of the Earth. These two temperatures are a function of the adiabatic compression of the atmosphere by gravity; the size of the compression is determined by the atmospheric mass and the planet’s gravity (this is why Venus has 460C surface temp.). Incoming absorbed radiation becomes outgoing long wave radiation that is, in turn, sourced by the surface, H2O gas and CO2; reflected radiation is per albedo.]]

    This is wrong from beginning to end. The static compression of an atmosphere by a planet’s gravity cannot possibly maintain the temperature of the atmosphere; unless work is being done, no heat will be generated. If high pressure were all there were to it, Neptune would be hot. Venus is hot because of the greenhouse effect, not because of some compression effect.

    [[Radiative transfer to the atmosphere is very small compared to evaporation and convection.]]

    On the contrary. The Earth contributes about 350 watts per square meter of longwave radiation to the atmosphere, but only 24 watts per square meter by conduction and convection and 78 watts per square meter from evaporation of seawater. Non-radiative effects are important, but they are in no way very large compared to the radiative effects. See:

    http://www.cgd.ucar.edu/cas/abstracts/files/kevin1997_1.html

    Comment by Barton Paul Levenson — 27 Aug 2007 @ 10:01 AM

  229. Dermod, the very change in density of which you speak could contribute to a thermal gradient via radiation: At higher altitudes, 1)absorption decreases, but still remains high; 2)the balance between re-radiation and other relaxation processes (e.g. collisional) shifts toward re-radiation. Thus, more energy is lost at higher altitude. Once in the stratosphere, the situation changes significantly due to absorption of UV by O3–this means that the atmosphere is warmer than would be expected in LTE, so CO2 and other ghgs have a net cooling effect.

    Comment by Ray Ladbury — 27 Aug 2007 @ 10:11 AM

  230. So this won’t be just a war of words, let me do a little relevant math here.

    The equation for the heat content of a substance is:

    H = m c T

    where H is the heat content (in Joules; I’ll use the SI), c the specific heat or heat capacity of the substance (in J kg-1 K-1), and T is the temperature (K).

    For dry air the heat capacity is 1,004 Joules per Kelvin per kilogram. A kilogram of air near the surface might have a mean global annual temperature of 288 K, a kilogram near the tropopause might be at 217 K. The heat content of 1 kilogram of air is therefore 289,000 Joules near the surface, and 218,000 Joules near the tropopause (maintaining the proper number of significant digits). The tropopause kilogram therefore has about 25% less thermal energy than the one near the surface.

    Comment by Barton Paul Levenson — 27 Aug 2007 @ 10:12 AM

  231. As a retired Physicist I have been trying for many years to find a convincing explanation of the atmospheric greenhouse effect. My difficulties all stem from the statements in your step 1.

    The radiative fluxes you mention appear to come from the Trenberth analysis. If the upward radiation energy from the surface is 390 watts per square meter, an anisotropic balancing downward flux from the atmosphere of 324 watts per square meter from the atmosphere is required.

    The net upward radiation from the surface is necessary, because otherwise there would be a net heating effect at the (warmer) surface, prohibited by the second law of thermodynamics. But if there is no heat transfer from the atmosphere to the surface, how can atmospheric radiation explain the observed surface temperature, and how can an increase in atmospheric radiation from increased CO2 plus additional H2O further increase the surface temperature?

    Incidentally, why does the atmosphere not radiate istropically in the Trenberth model?

    [Response: The numbers are similar to those in Kiehl+Trenberth because they used the same observational constraints. There is no ambiguity there - TOA LW out is measured, surface LW up is also measured (and fits a near blackbody curve). The difference between the two is evidence of net LW absorption in the atmosphere. Your confusion I think stems from thinking of the atmosphere as a single layer at a single temperature. It is not, and given the temperature gradient, the mean emission level (at 255 K) does not have to be at the same height as the mean absorption level. You can in fact simply add an extra layer to the KT analysis to make it all work out as you expect. - gavin]

    Comment by Fred Staples — 27 Aug 2007 @ 10:49 AM

  232. Re 226,230,219, – nice job.

    Re 228 – but don’t forget that near the surface, the net LW radiation flux is smaller than net convective flux. But as I tried to explain before, this does not mean that LW fluxes are relatively unimportant. (But neither is convection – if convection were artificially held back, then the lapse rate would change until pure radiative equilibrium could be attained – the lower tropospheric lapse rate would be higher and the surface warmer. If there were no LW radiation at all, then the Earth would heat up until it was hot enough to emit SW significantly (as convection does not go into space). if there were no downward LW flux from the atmosphere to the surface, than the net LW flux from the surface would rise drastically, cooling the surface and warming the atmosphere, while reducing the upward convective flux…etc…)

    Re 229 – I thought that LTE was still a good approximation for reality up to … well, very high up – maybe into the lower thermosphere? I don’t think it is necessary to have a departure from LTE (local thermodynamic equilibrium) to explain things – SW energy is absorbed – there are chemical reactions involved, but the end effect of that is solar heating of the upper atmosphere, particularly the upper stratosphere. It heats up until LW radiative flux divergence balances the SW flux convergence.

    Re 221 – models used by the IPCC take both convection and radiation into account – if they did not, the results would be WAY off. (I’m not sure if this is your point, but some people try to argue that since convection greatly reduces the equilibrium temperature of the surface and lowermost troposphere (relative to pure radiative equilibrium), which is true, then the warming by any additional greenhouse effect will be drastically reduced or maybe completely whisked away by convection – well, that last version is certainly false – maybe it is reduced, but the thing is, this (convective adjustment) is included in the models, and thus cannot support a ‘models are wrong’ arguement).

    Re 225 – the thermal expansion of the troposphere is not why the upper atmosphere cools – the thermal expansion of the troposphere lifts the pressure levels upward a bit, so the upper atmosphere (setting aside shifting location of the tropopause) is lifted up by the same amount that the pressure levels are raised – there is no expansion of the upper atmosphere associated with this process, and thus no cooling. (Except maybe that, being further from the center of the Earth, gravitational acceleration is weaker, so that the weight of the upper atmosphere is reduced (shifting pressure levels back down some amount) – but that would be a rather small effect, considering the tropopause is less than 20 km high and the expansion would be around 1% (with some additional expansion due to additional water vapor content) – and perhaps reduced or cancelled or reversed by the contraction of the upper atmosphere that occurs as it does cool.)

    The reason the upper atmosphere cools is that 1. as the LW opacity increases, less of the warmer surface and lower troposphere can be ‘seen’ from the upper atmosphere – it looks colder looking down, and 2. the upper atmosphere can be seen better (in the LW) from space, meaning that it becomes a more effective emitter, radiative more LW to space at a given temperature, so that it cools until LW balance is restored. The cooler upper atmosphere reduces the change in LW radiative forcing at the tropopause, but not greatly – radiative forcing still exists – that is, there is an imbalance that causes the troposphere and surface to warm. As the troposphere warms and stratosphere cools, the tropopause height rises – not just by thermal expansion, but by redesignation of the air in lower edge of stratosphere – in other words, I think the tropopause height rises to a lower pressure surface (surface in the abstract sense of the word). The warmer troposphere does reduce the cooling of the upper atmosphere by some amount (by increased LW heating from below) but it still ends up cooler.

    Re 224 – The greenhouse effect creates the troposphere. With no greenhouse effect, the surface could cool directly to space by radiation. There would be no convection without the greenhouse effect (another reason why LW radiation is important even at the surface) (setting aside large-scale horizontal variations – see previous comments) because there would not be a radiative heating distribution that would tend to destabilize a portion of the atmosphere (at least not while near an equilibrium state). Increasing LW opacity generally tends to increase the depth (in pressure coordinates as well as geometric or geopotential height coordinates) of the troposphere at the expense of the remaining upper atmosphere.

    The greenhouse effect is weaker in areas of higher elevation – all else being equal (at a given pressure level) – the remaining atmosphere above an elevated region has less optical depth, so more LW radiation can escape directly to space; there is also less remaining troposphere in particular, so more LW radiation can escape to the relatively cooler upper troposphere and lower stratosphere – these effects may not be as significant if the optical depth remaining in the whole atmosphere or in particular the mid-troposphere is still high (which can be expected if there are clouds or high humidity, or in some wavelength ranges, although in clear sky, I would expect significant effects within or on the edges of the atmospheric window (a band of relative transparency between 8 and 12 microns, interupted by ozone around 9 or 10 microns, and blocked by clouds or low-level high humidity, partially blocked by lower level humidity, bounded by CO2 absorption/emission at the long wavelength end), or on the edges of other absorption bands, etc. Anyway, as colder parts of the atmosphere can be ‘seen’ in the LW in general, the net LW emission from the surface will be higher at a given temperature as there is less downward LW emission, thus the equilibrium surface temperature will be cooler. Even comparing high elevation to low elevation in very opaque circumstances (fog/clouds), that the air tends to be cooler at higher elevations anyway (because a cloudy layer will have a net LW radiation from the top of the clouds, or would tend to convect upward if it became warmer, as upper level air may be advected from somewhere and still be cold, etc…) means that there is less downward LW radiation at the surface. Overall, less downward LW radiation (and to a degree, a tendency for a greater amount of SW radiation to reach higher elevations) places greater relative influence on the SW radiation flux in maintaining the temperature, which means that there will be a tendency for greater diurnal variation. That’s not all; while the greenhouse effect is lower at higher elevations, I don’t think it automatically follows that the equilibrium temperature will be the same as at the same pressure level over lower elevations – direct solar heating of the surface can increase the temperature over a plateau relative to that at the same level over a lower plain. This can drive wind upslope. In the diurnal cycle, there are mountain-valley breezes (at night, the mountain cools off faster) as well as land-sea breezes, and similarly, the Tibetan plateau plays a role in the seasonal Asian monsoons. In the summer or in midday, dry air (if not cloudy air) blowing up a slope can have a cooling effect on the upper elevations owing to the adiabatic lapse rate.

    ——————
    PS the optical properties of each unit of atmosphere change with pressure as well as composition (the heterogeniety of water vapor, clouds, aerosols, ozone). An individual atom or molecule has a line spectrum. Quantum uncertainty causes some (relatively small, I think) broadenning of those lines. Collisional (pressure) broadenning occurs, as energy levels are altered. The doppler effect due to molecular motion also broadens the lines. Interaction among molecules can also create more lines, which may happen with water vapor at relatively high concentrations (the atmospheric window closes up with high enough water vapor concentration, even before it becomes cloudy (if the temperature is high enough)). Bands may contain many lines, etc…; going upward, there is generally less line broadenning, so gaps between the lines become clearer, but this is balanced by increased optical cross sections (at a single wavelength, cross section per molecule * molecules per unit volume = optical depth per unit distance) – that is, for line broadenning mechanisms, I think the total cross section integrated over wavelength remains the same (without weighting by radiation as a function of wavelength); however, the same is not true for optical depth when the optical depth is not very close to zero. The average effective optical depth over wavelength should decrease when line broadenning decreases because the increased optical depth at line peaks has a saturation effect (each unit increase in optical depth has progressively less impact on remaining trasmission). Anyway, this (changes in line broadenning) alters the optical depth per unit distance as a function of height, but this modifies the major effects discussed; it doesn’t really create them – it is not the reason the upper atmosphere above the tropopause cools in response to increased greenhouse effect.
    ———————-

    Comment by Patrick 027 — 27 Aug 2007 @ 8:55 PM

  233. Patrick, can you add some references for those many statements?

    http://mustelid.blogspot.com/2005/03/why-does-stratosphere-cool-under-gw.html

    Comment by Hank Roberts — 27 Aug 2007 @ 11:56 PM

  234. Re: #230

    “For dry air the heat capacity is 1,004 Joules per Kelvin per kilogram. A kilogram of air near the surface might have a mean global annual temperature of 288 K, a kilogram near the tropopause might be at 217 K. The heat content of 1 kilogram of air is therefore 289,000 Joules near the surface, and 218,000 Joules near the tropopause (maintaining the proper number of significant digits). The tropopause kilogram therefore has about 25% less thermal energy than the one near the surface.”

    Correct, but you’re still leaving out gravitational potential energy. A kg of air at 10 km will have 98,000 Joules of gravitational potential energy (g*h/kg, where g=9.8m/sec2 is the acceleration from gravity and h is the height in meters. An atmosphere with just nitrogen and oxygen would still have a lapse rate of about 10 K/km. It would be a lot colder, though.

    Comment by DeWitt Payne — 29 Aug 2007 @ 7:23 PM

  235. Re 233 – well, I did that mainly by memory and reasoning – are there specific parts you disagree with?

    Comment by Patrick 027 — 29 Aug 2007 @ 7:37 PM

  236. Just too many statements to sort out what’s what, and I’ve become convinced that I need cites to be sure I understand what I read.

    Comment by Hank Roberts — 29 Aug 2007 @ 8:42 PM

  237. Re 215 Patrick, quoting you “Re 210 – and gravity, yes, the convectively maintained lapse rates depends on gravity” Er, Patrick what is a “convectively maintained lapse rate”? Is this a new physical mechanism, finally it is discovered that the cause produces the effect!! I tried this when I was at school but it didn’t work, lucky you!

    Re#230 quoting Barton “The equation for the heat content of a substance is:

    H = m c T

    where H is the heat content (in Joules; I’ll use the SI), c the specific heat or heat capacity of the substance (in J kg-1 K-1), and T is the temperature (K).

    For dry air the heat capacity is 1,004 Joules per Kelvin per kilogram.”

    Very interesting Barton, but is there a good reason for using the Cp (constant pressure) specific heat? http://www.engineeringtoolbox.com/air-properties-d_156.html

    I was using an adiabatic model and I said so more than once; if you use another we will never get to a common position and we are wasting everybody’s time. This whole matter is not the easiest to grasp and this kind of approach produces endless playground arguments, ’tis, ’tisn’t, ’tis, ’tisn’t etc. etc.

    Comment by Dermod O'Reilly — 30 Aug 2007 @ 2:25 PM

  238. Re 237 – a convectively maintained lapse rate will tend to occur when convection is allowed, which will be when and where the lapse rate without convection would become great enough to be unstable to that convection.

    Cp is used in the atmosphere for specific heat because it is held at (essentially) constant pressure by it’s own mass under gravity. It is not held at constant volume. Of course air can move up and down and change pressure that way, and then one gets adiabatic temperature changes (or moist adiabatic if at 100 % relative humidity – if water phase changes are occuring). A way to view this is in very small steps, that is, for example, if air is rising, there is a change in pressure per unit time. There is a dry adiabatic temperature decline per unit decrease in pressure. If at 100% relative humidity, there is an amount of latent heat release …

    (a diabatic process for the air by itself – it can also be called moist adiabatic because as long as the condensed water does not get seperated from the same air (or as long as there is not mixing between air parcels of different characteristics), the process is isentropic and reversable)

    … per unit decrease in pressure due to the cooling. There could also be some other diabatic heating from radiation flux convergence. The latent and other diabatic heating causes a change in temperature, which can be found using Cp if at constant pressure. This can be done if the diabatic heating is added not during but after each increment in change in pressure. This can be made to be realistic by shrinking the increments toward size zero – that’s calculus.

    ———-

    Another thought on upper atmosphere cooling by adiabatic expansion – even if that were to occur, it would be an instantaneous effect that, if radiative or radiative-convective equilibrium were not changed, would eventually disappear from radiative heating. It is the change in radiative-convective equilibrium that causes upper atmospheric cooling.

    Comment by Patrick 027 — 30 Aug 2007 @ 6:46 PM

  239. [[Very interesting Barton, but is there a good reason for using the Cp (constant pressure) specific heat?]]

    Okay, use the constant volume specific heat and see if it changes your results substantially. You still get that the one at the tropopause has 25% less thermal energy.

    Comment by Barton Paul Levenson — 31 Aug 2007 @ 8:00 PM

  240. To all who respond:
    [edit] There are some of us who are not skeptics, but do not want to blindly copy the words of others either. I for one just want to learn more before I start formulating an opinion. Information seems to be conflicting. One chart shows CO2 lagging temperature, and levels as seen before, and others show CO2 at levels double than ever before. Having a forum like this is great because I can ask people who might actually gather their own data.

    So are we experiencing the highest temperature and CO2 ever? Or has the earth been through this before?

    Offer information so we can all learn.
    If they don’t understand, explain it more clearly.
    Thank you to those who choose not get angry.

    Comment by Joanna — 31 Aug 2007 @ 9:25 PM

  241. [[So are we experiencing the highest temperature and CO2 ever? Or has the earth been through this before]]

    Neither is at a record level when the records under discussion span the history of the Earth. But it has been 10,000 years since we’ve experienced a climate change this major, and our agriculture and our economy depend on the climate we have now — or had before 1970, say. The increased droughts in continental interiors, increased violent weather along coastlines, and gradually submerging of coastal cities, will play merry hell with our civilization. If we can mitigate the worst effects by acting now we ought to try.

    Comment by Barton Paul Levenson — 1 Sep 2007 @ 6:27 AM

  242. Joanna, try the “Start Here” link, at the top of each page, for answers to frequently asked questions like yours.
    Also try the list in the right hand column of each page, for major topics discussed earlier at RC, and the Science links.
    (I’m just another reader here, not one of the climate scientists).
    (You can usually find the answers to off-topic questions, in the links and lists provided.)

    Comment by Hank Roberts — 1 Sep 2007 @ 9:31 AM

  243. Re #240: Joanna — At the top of the page ther is a link to the

    Start Here

    page. After that, there is a link on the side bar to the

    AIP Dicovery of Global Warming

    page. Both a great resources to help you get started. Enjoy!

    Comment by David B. Benson — 1 Sep 2007 @ 1:51 PM

  244. Re #240

    Joanna,

    The Earth has been through this before, but not mankind. One case was during the PETM see http://en.wikipedia.org/wiki/Paleocene-Eocene_Thermal_Maximum

    But also during the Jurassic and Cretaceous, when the dinosaurs ruled the world, carbon dioxide levels were much higher and the climate was much warmer. The cold blooded reptiles would not have survived if had not been warmer.

    During the warmings which end the glaciations the temperature rise does lead the CO2 rise. However, we are pretty sure that it is variations in the orbit of the earth around the sun (Milankovitch cycles) which causes us to enter and leave those glacial periods. The CO2 acts as a feedback amplifying those astronomical effects.

    Milankovitch cycles explain why we go in and out of glacial periods, but they do not explain why this ice age has started. Milankovitch cycles happened during the Cretaceous but there was no ice then. It seems that the reason is that during the PETM a new type of plant, C$ grasses, evolved to survive the heat. These plants are more efficient at using carbon dioxide and they have reduced the level of global CO2, eventually causing the start of the current ice age.

    So we are fairly confident that past climate change has been caused by changes in CO2 level, along with other factors.

    Comment by Alastair McDonald — 1 Sep 2007 @ 2:22 PM

  245. Re 240 – on the matter of “So are we experiencing the highest temperature and CO2 ever? Or has the earth been through this before?”

    I’m not sure of the sustained rate of CO2 rise, but in terms of the amount of CO2 and the potential increase in global temperature we will see, the Earth certainly has been through such conditions before. It has been hotter, and has been colder, perhaps even much colder. It has had much lower sea levels, and also much higher sea levels (not just from an absense of large ice sheets – there is also the matter of geological forces changing the relative heights of continental and oceanic crust). And the continents have been in a number of different arrangements. But that’s not really at issue. Humans wouldn’t necessarily have wanted to be around at certain times in the past (not in large numbers, anyway). Changes which are both sufficiently large and rapid can cause mass extinctions (it takes time for species and ecosystems to adapt and migrate to change). And sufficiently large and rapid changes will be of concern for us, our economies and societies.

    Comment by Patrick 027 — 1 Sep 2007 @ 4:56 PM

  246. Re 240 – another point – even if, on occasion, a large and even somewhat rapid change can take place, there is the matter of would we be expecting such a change in the forseeable future besides those we could cause or control. I think the likelihood of a sizable asteroid impact, prolonged flood volcanism (which I don’t think would even be all that rapid compared to our effects, or even iceage-interglacial transisitions), or supervolcano eruption occuring within the next few thousand years is small enough that we should be concerned about anthropogenic global warming. (The next ice age is likely a few tens of thousands of years into the future.)

    Comment by Patrick 027 — 1 Sep 2007 @ 9:37 PM

  247. Re: Joanna (#240)

    CO2 levels have both lead and followed temperatures in the past. For example, during the Permian-Triassic Extinction (the greatest major extinction – approximately 251 million years ago, you could look it up in Wikipedia – but I wouldn’t worry too much about our reaching levels quite like that), CO2 levels lead, being the result of a Siberian supervolcano resulting from the continental collision. The CO2 levels rose to perhaps over 3000 ppm, and the volcano continued to erupt lava for over a million years.

    CO2 absorbs longwave thermal radiation from the earth’s surface (a process that is well-understood), making the atmosphere opaque to radiation in those parts of the spectra, reemits much of it to the earth’s surface, warming the surface, causing higher levels of water evaporation. More water vapor means more absorption of thermal radiation and more reemission to the surface. This amplifies the effects of carbon dioxide – as does the melting of ice and consequent greater absorption of sunlight by the earth’s surface. However, water vapor won’t stay in the atmosphere for very long without the continued presence of other greenhouse gases. It falls out as rain or snow. But carbon dioxide tends to stay in the atmosphere for a very long time.

    With higher temperatures you have the reduction in the ability of the ocean to absorb gases, including both carbon dioxide and oxygen. Depending upon how high the temperatures rise, the ocean may even become a net emitter – much like soda going flat. If temperatures go high enough, thawing permafrost and shallow water methane cathrates may become an emitters as well, but methane tends to degrade into carbon dioxide within a matter of decades. Higher temperatures will result in plants suffering from heat and drought stress (higher temperatures mean more evaporation from the soil and the expansion of the Hadley cells), and thus they will be less able to absorb carbon dioxide.

    So basically there is a great deal of positive feedback between temperatures and carbon dioxide. It doesn’t really matter what gets the process rolling so much as the fact that the system is in disequilibrium and positive feedback will shift the climate system away from the original equilibrium to a new equilibrium. Ultimately the excess CO2 will end up being mineralized before a final equilibrium is reached, but it will start to decline well before then.
    *
    In any case, setting aside the extinctions, we have the ability to cause a great deal of damage by human standards. While the IPCC has projected that business as usual will result in less than a meter of sea-level rise in this century, they have assumed that it is a linear process, we are seeing more and more that it is anything but. The arctic warms as more dark ocean is exposed by melting sea ice, melting snow is darker and absorbs more sunlight, drainage from glaciers lubricate the bottom of those glaciers so that they slide more quickly towards the ocean, and if either Greenland or the West Antarctic Peninsula melts enough, positive feedback will be come into play where the rising sea-levels will reach more ice and even lift the glaciers so that they descend more rapidly into the ocean. It is possible that under business as usual we will see five meters this century due to such feedback.

    Since half the world’s population lives within sixty miles of the coasts, this is something to worry about. Since we expect the glaciers of the Tibetean Plateau to be gone by the end of this century and they are what feed the six major rivers of Asia, this is something to worry about. Since global warming is already resulting in droughts becoming more frequent (with the amount of the world being in drought at any given time rising from 20% in the 1950s to 30% today and projected to rise to 50% by the end of this century), this is something to worry about. We are talking about large populations of people being displaced, drastic reductions in agricultural output, and drastic reductions in fish harvests (due to the increasing acidity of the ocean – another effect of rising atmospheric levels of carbon dioxide).

    Cities aren’t that portable. There is a great deal of infrastructure that they depend upon – and even if they aren’t permanently flooded by rising sea-levels, they will be more vulnerable to stronger storms and the rising sea levels may render them uninhabitable if the subways or sewers become flooded. Farmland isn’t portable – and we are looking at the United States being unable to grow even wheat in the lower forty-eight by 2080.

    So the economic consequences are projected to be quite severe. We may be looking at an economic crisis which will be deeper than the Great Depression and which will last far longer if we do not adjust our course. Finally, if we encounter a major economic recession before that, it will quickly reduce the amount of aerosols which have been masking much of the effects of the carbon dioxide which is already in the atmosphere. Temperatures could rise much more quickly.

    I hope this helps.

    Comment by Timothy Chase — 2 Sep 2007 @ 12:56 PM

  248. Great post which has certainly improved my understanding particularly in relation to saturation, and an explanation of why the stratosphere has cooled. Is it correct to say that the two key factors are the temperature required at the top of the troposphere where the radiated heat is effectively transmitted into space and the height at which this occurs? From this the lapse rate determines the surface temperature (average temperatures of course). Additional CO2 has two effects. One is additional absorption by the “wings” which has to be made up by an increase in temperature at the top of the troposphere. The second effect is an increase in the opacity of the atmosphere at infrared which therefore increases the height at which the effective radiation occurs. So the temperature of the atmosphere required to generate 240W/m2 of radiation needs to occur higher and again this translates directly to a higher surface temperature. In which case, is it also true that the increase in temperature occurs relatively quickly (weeks/months) from the time of the increase in concentrations, and if this is the case can the effect be directly observed in areas where the CO2 (and methane) concentrations are highest (it appears from this http://www.eoearth.org/article/Visualization_of_the_global_distribution_of_greenhouse_gases_using_satellite_measurements that there are quite wide seasonal and regional variations in the concentrations of GHG’s). The reason why the adjustment would occur quickly is that the additional heat being added to the atmosphere by absorption of the wings is not what is actually doing the heating, the whole of the solar flux is available to drive the system to it’s new equilibrium.

    Comment by Fred — 3 Sep 2007 @ 5:21 AM

  249. “If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations — then so much the worse for Maxwell’s equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.”
    – Sir Arthur Eddington

    This very interesting debate gets very close to the heart of the AGW “greenhouse” theory.

    Without any radiative effects, Mr O’Reilly’s thermodynamic arguments leaves the atmosphere with an approriate pressure/temperature gradient, and the earth’s outgoing and incoming radiation in balance at the tropopause.

    The crucial issue is contained in an aside from DeWitt Payne:

    234 “An atmosphere with just nitrogen and oxygen would still have a lapse rate of about 10 K/km. It would be a lot colder, though.”

    Would it? Do the greenhouse gasses warm the earth to any significant extent?

    Almost 100 years ago Mr RWWood attempted to settle the matter. He constructed a radiative (glass) and non-radiative (rock-salt) enclosure, exposed them both to sunlight, and found no detectable radiative effect from the glass. The temperature in both the enclosures reached 65 degrees centigrade.

    He concluded:

    “Is it therefore necessary to pay attention to trapped radiation in deducing the temperature of a planet as affected by its atmosphere? The solar rays penetrate the atmosphere, warm the ground which in turn warms the atmosphere by contact and by convection currents. The heat received is thus stored up in the atmosphere,
    remaining there on account of the very low radiating power of a gas. It seems to me very doubtful if the atmosphere is warmed to any great extent by absorbing the radiation from the ground, even under the most favourable conditions.

    I do not pretend to have gone very deeply into the matter, and publish this note merely to draw attention to the fact that trapped radiation appears to play but a very small part in the actual cases with which we are familiar.”

    His generation of Physicists ignored Arrhenius. Would it have been a good idea to have taken him seriously, and to have foregone the technological developments in the 20th century to avoid his predicted 6 degree rise in surface temperature?

    Comment by Fred Staples — 10 Sep 2007 @ 7:57 AM

  250. Fred Staples, the greenhouse effect is known physics. It’s good for about 33 K warming of the planet. There is nothing that is even the least bit controversial there.

    Comment by Ray Ladbury — 10 Sep 2007 @ 8:58 AM

  251. “Emission and dissociation of molecular nitrogen in the earth’s atmosphere”
    http://www.onderzoekinformatie.nl/en/oi/nod/onderzoek/OND1288464/

    “…. In this area of research, our databases are highly incomplete. In the case of nitrogen many electronic states have not been discovered or have not been characterized. States that may be formed upon electron or photon impact on nitrogen gas in the atmosphere. …”

    The researchers are still working on this; Wikipedia’s article uses the word “significantly” and that probably covers the unknown modes being looked at mentioned above.

    http://en.wikipedia.org/wiki/Greenhouse_effect
    “…. The molecules/atoms that constitute the bulk of the atmosphere: oxygen (O2), nitrogen (N2) and argon; do not interact with infrared radiation significantly. While the oxygen and nitrogen molecules can vibrate, because of their symmetry these vibrations do not create any transient charge separation. Without such a transient dipole moment, they can neither absorb nor emit infrared radiation. In the Earth’s atmosphere, the dominant infrared absorbing gases are water vapor, carbon dioxide, and ozone (O3). The same molecules are also the dominant infrared emitting molecules….. Roughly 5% of CO2 molecules are vibrationally excited at room temperature and it is this 5% that radiates. A substantial part of the greenhouse effect due to carbon dioxide exists because this vibration is easily excited by infrared radiation. CO2 has two other vibrational modes. The symmetric stretch does not radiate, and the asymmetric stretch is at too high a frequency to be effectively excited by atmospheric temperature collisions, although it does contribute to absorption of IR radiation….”

    Comment by Hank Roberts — 10 Sep 2007 @ 1:41 PM

  252. I just wanted to ask a climate expert if there is any evidence that suggested that submarine volcanos may be responsible for the recent rise in co2. I have read the thread regarding climate and volcanos but that didn’t answer my question. Volcanos on the land surface appear to be important but not responsible, however most volcanos are submarine (>75 % ?) and very difficult to detect. Most are still undiscovered.

    Comment by David — 11 Sep 2007 @ 3:42 AM

  253. [[234 “An atmosphere with just nitrogen and oxygen would still have a lapse rate of about 10 K/km. It would be a lot colder, though.”

    Would it? Do the greenhouse gasses warm the earth to any significant extent? ]]

    Yes. The emission temperature of the Earth can be found from:

    Fg = (S / 4) (1 – A)

    and

    Te = (Fg / σ)0.25

    where Fg is the net radiative flux received by the planet, S the solar constant (canonical value 1367.6 watts per square meter), A the Earth’s bolometric Bond albedo (0.306 according to NASA), and σ the Stefan-Boltzmann constant (5.6704 x 10-8 W m-2 K-4). This gives a net radiative flux of 237.3 W m-2 and Te = 254° K. You probably know that the freezing point of water is 273° K. The surface temperature of the Earth averages 288° K. Without that 33° K. from the greenhouse effect, the Earth would be frozen solid.

    Comment by Barton Paul Levenson — 11 Sep 2007 @ 6:04 AM

  254. > most volcanos are submarine (>75 % ?) and very
    > difficult to detect. Most are still undiscovered.

    Maybe so, but how do you know this? What’s your source?

    The best available information I find by looking is the recently declassified Navy acoustic tracking data. This for example:

    http://www.tos.org/oceanography/issues/issue_archive/issue_pdfs/20_1/20.1_juniper_et_al.pdf

    “During the 1990s, civilian access to the SOSUS acoustic listening network in the Northeast Pacific provided researchers with the means for remotely detecting seafloor eruptions on the Juan de Fuca and Gorda Ridges. Event-response studies at eruption sites in this region (Embley et al., 1999), together with the serendipitous discovery and follow-up investigation of a seafloor eruption at 9�N on the East Pacific Rise (Haymon et al., 1993; Shank et al., 1998), greatly increased our appreciation of the hydrothermal and biological consequences of magma injection and eruption events. These same studies documented the impressive capacity of microorganisms (Juniper et al., 1995; Huber et al., 2003) and vent fauna (Tunnicliffe et al., 1997) to quickly colonize and exploit new sources of venting, and reinvigorated research into the propagation of vent species along mid-ocean ridges.”

    Comment by Hank Roberts — 11 Sep 2007 @ 10:17 AM

  255. David (#252). Where do people get these ideas? First, submarine volcanos are not hard to find–they put out a low of heat, ash, etc. Second, CO2 solubility in water increases with pressure–at depth most of the CO2 would just dissolve in the deep oceans and stay there. This is in fact what happens in volcanic lakes like Lake Nyos–the CO2 dissolves in the deep waters, increases the density of the water, and the lake stratifies, at least until something overturns the deep waters and there is a cataclysmic release of CO2. Third, why would volcanic activity in the oceans suddenly increase, but not on land? And on and on. Finally, there is no problem accounting for the increase in CO2–humans have produced more than enough to account for the rise. In fact, much of what we produce still goes into the oceans.

    Comment by Ray Ladbury — 11 Sep 2007 @ 10:35 AM

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