The CO2 problem in 6 easy steps
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. The explanation has a number of separate steps which tend to sometimes get confused and so we will try to break it down carefully.
Step 1: There is a natural greenhouse effect.
The fact that there is a natural greenhouse effect (that the atmosphere restricts the passage of long wave (LW) radiation from the Earth's surface to space) is easily deducible from i) the mean temperature of the surface (around 15ºC) and ii) knowing that the planet is roughly in radiative equilibrium. 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.
Step 2: Trace gases contribute to the natural greenhouse effect.
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 (Harries et al, 2001; HITRAN). The only question is how much energy is blocked by each. This cannot be calculated by hand (the number of absorption lines and the effects of pressure broadening etc. preclude that), but it can be calculated using line-by-line radiative transfer codes. The earliest calculations (reviewed by Ramanathan and Coakley, 1979) give very similar results to more modern calculations (Clough and Iacono, 1995), and demonstrate that removing the effect of CO2 reduces the net LW absorbed by ~14%, or around 30 W/m2. For some parts of the spectrum, IR can be either absorbed by CO2 or by water vapour, and so simply removing the CO2 gives only a minimum effect. Thus CO2 on its own would cause an even larger absorption. In either case however, the trace gases are a significant part of what gets absorbed.
Step 3: The trace greenhouse gases have increased markedly due to human emissions
CO2 is up more than 30%, CH4 has more than doubled, N2O is up 15%, tropospheric O3 has also increased. New compounds such as halocarbons (CFCs, HFCs) did not exist in the pre-industrial atmosphere. All of these increases contribute to an enhanced greenhouse effect.
Step 4: Radiative forcing is a useful diagnostic and can easily be calculated
Lessons from simple toy models and experience with more sophisticated GCMs suggests that any perturbation to the TOA radiation budget from whatever source is a pretty good predictor of eventual surface temperature change. Thus if the sun were to become stronger by about 2%, the TOA radiation balance would change by 0.02*1366*0.7/4 = 4.8 W/m2 (taking albedo and geometry into account) and this would be the radiative forcing (RF). An increase in greenhouse absorbers or a change in the albedo have analogous impacts on the TOA balance. However, calculation of the radiative forcing is again a job for the line-by-line codes that take into account atmospheric profiles of temperature, water vapour and aerosols. The most up-to-date calculations for the trace gases are by Myrhe et al (1998) and those are the ones used in IPCC TAR and AR4.
These calculations can be condensed into simplified fits to the data, such as the oft-used formula for CO2: RF = 5.35 ln(CO2/CO2_orig) (see Table 6.2 in IPCC TAR for the others). 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). Forcings for lower concentration gases (such as CFCs) are linear in concentration. The calculations in Myrhe et al use representative profiles for different latitudes, but different assumptions about clouds, their properties and the spatial heterogeneity mean that the global mean forcing is uncertain by about 10%. Thus the RF for a doubling of CO2 is likely 3.7±0.4 W/m2 - the same order of magnitude as an increase of solar forcing by 2%.
There are a couple of small twists on the radiative forcing concept. One is that CO2 has an important role in the stratospheric radiation balance. The stratosphere reacts very quickly to changes in that 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. The other wrinkle is depending slightly on the spatial distribution of forcing agents, different feedbacks and processes might come into play and thus an equivalent forcing from two different sources might not give the same response. The factor that quantifies this effect is called the 'efficacy' of the forcing, which for the most part is reasonably close to one, and so doesn't change the zeroth-order picture (Hansen et al, 2005). This means that climate forcings can be simply added to approximate the net effect.
The total forcing from the trace greenhouse gases mentioned in Step 3, is currently about 2.5 W/m2, and the net forcing (including cooling impacts of aerosols and natural changes) is 1.6±1.0 W/m2 since the pre-industrial. Most of the uncertainty is related to aerosol effects. Current growth in forcings is dominated by increasing CO2, with potentially a small role for decreases in reflective aerosols (sulphates, particularly in the US and EU) and increases in absorbing aerosols (like soot, particularly from India and China and from biomass burning).
Step 5: Climate sensitivity is around 3ºC for a doubling of CO2
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.). Given that it doesn't matter much which forcing is changing, sensitivity can be assessed from any particular period in the past where the changes in forcing are known and the corresponding equilibrium temperature change can be estimated. 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). More formally, you can combine this estimate with others taken from the 20th century, the response to volcanoes, the last millennium, remote sensing etc. to get pretty good constraints on what the number should be. This was done by Annan and Hargreaves (2006), and they come up with, you guessed it, 3ºC.
Converting the estimate for doubled CO2 to a more useful factor gives ~0.75 ºC/(W/m2).
Step 6: Radiative forcing x climate sensitivity is a significant number
Current forcings (1.6 W/m2) x 0.75 ºC/(W/m2) imply 1.2 ºC that would occur at equilibrium. Because the oceans take time to warm up, we are not yet there (so far we have experienced 0.7ºC), and so the remaining 0.5 ºC is 'in the pipeline'. We can estimate this independently using the changes in ocean heat content over the last decade or so (roughly equal to the current radiative imbalance) of ~0.7 W/m2, implying that this 'unrealised' forcing will lead to another 0.7×0.75 ºC - i.e. 0.5 ºC.
Additional forcings in business-as-usual scenarios range roughly from 3 to 7 W/m2 and therefore additional warming (at equilibrium) would be 2 to 5 ºC. That is significant.
Q.E.D.?
6 August 2007 at 4:41 PM
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.
6 August 2007 at 5:08 PM
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.
6 August 2007 at 5:21 PM
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.
6 August 2007 at 5:46 PM
Q.E.D.
The six step explaination is most clear. Thank you.
6 August 2007 at 5:57 PM
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!
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?
6 August 2007 at 7:38 PM
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]
6 August 2007 at 8:05 PM
Konstantin, this may help:
http://initforthegold.blogspot.com/2007/07/first-meter.html
6 August 2007 at 8:45 PM
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.
6 August 2007 at 9:20 PM
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….
6 August 2007 at 9:32 PM
Konstantin (#6) wrote:
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:
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.
6 August 2007 at 10:35 PM
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,” 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
6 August 2007 at 10:55 PM
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.
6 August 2007 at 11:43 PM
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.
7 August 2007 at 12:51 AM
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.
7 August 2007 at 2:39 AM
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
7 August 2007 at 3:37 AM
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]
7 August 2007 at 5:16 AM
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).
7 August 2007 at 5:47 AM
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]
7 August 2007 at 6:04 AM
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)
7 August 2007 at 6:18 AM
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
7 August 2007 at 6:37 AM
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.
7 August 2007 at 6:50 AM
[[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?
7 August 2007 at 7:03 AM
[[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.
7 August 2007 at 7:12 AM
Danny Bee could also help by turning off his computer.
7 August 2007 at 7:35 AM
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…
7 August 2007 at 9:08 AM
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.
7 August 2007 at 9:09 AM
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.
7 August 2007 at 9:46 AM
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]
7 August 2007 at 10:22 AM
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]
7 August 2007 at 10:37 AM
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?
7 August 2007 at 10:43 AM
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.
7 August 2007 at 10:44 AM
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.
7 August 2007 at 11:06 AM
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…
7 August 2007 at 11:09 AM
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.
7 August 2007 at 11:50 AM
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
7 August 2007 at 11:55 AM
# 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.
7 August 2007 at 12:34 PM
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…
7 August 2007 at 12:34 PM
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”
7 August 2007 at 12:38 PM
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
7 August 2007 at 12:45 PM
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.
7 August 2007 at 12:58 PM
Chuck Booth (#37) wrote:
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/
7 August 2007 at 1:31 PM
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.
7 August 2007 at 1:51 PM
George Peabody (#38) wrote:
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.
7 August 2007 at 2:08 PM
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.
7 August 2007 at 2:14 PM
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]
7 August 2007 at 2:50 PM
“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]
7 August 2007 at 2:55 PM
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.
7 August 2007 at 3:43 PM
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]
7 August 2007 at 3:56 PM
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…
7 August 2007 at 4:14 PM
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.
7 August 2007 at 4:39 PM
Thanks for the link David B.
7 August 2007 at 5:03 PM
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
7 August 2007 at 5:14 PM
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
7 August 2007 at 5:20 PM
“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]
7 August 2007 at 6:42 PM
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]
7 August 2007 at 7:34 PM
Re:44 Timothy Chase
Now you have gone and misspelled “spelling B” (its Bee), which is almost as funny as dust bowel
7 August 2007 at 7:55 PM
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?
7 August 2007 at 8:17 PM
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]
7 August 2007 at 9:20 PM
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.
7 August 2007 at 10:09 PM
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.
7 August 2007 at 10:19 PM
Chuck Booth (#40) wrote:
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.
8 August 2007 at 1:00 AM
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.”
8 August 2007 at 1:34 AM
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.
8 August 2007 at 4:08 AM
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.
8 August 2007 at 4:58 AM
[[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.
8 August 2007 at 5:02 AM
[[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.
8 August 2007 at 5:06 AM
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.
8 August 2007 at 8:30 AM
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.
8 August 2007 at 8:31 AM
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.
8 August 2007 at 8:35 AM
Re #69 Sorry, rereading #10 it’s internally inconsistent, at another point saying “all plane and vehicular transport”. And it does say NOW.
8 August 2007 at 9:41 AM
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.
8 August 2007 at 10:22 AM
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]
8 August 2007 at 10:24 AM
> http://en.wikipedia.org/wiki/European_Science_and_Environment_Forum
Oh, ick. I’d forgotten. Shudder.
8 August 2007 at 11:10 AM
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.
8 August 2007 at 11:27 AM
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.
8 August 2007 at 11:49 AM
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….
8 August 2007 at 12:08 PM
[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]
8 August 2007 at 12:26 PM
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?
8 August 2007 at 12:47 PM
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.
8 August 2007 at 12:52 PM
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.
8 August 2007 at 1:02 PM
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.
8 August 2007 at 1:25 PM
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.
8 August 2007 at 1:44 PM
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!
8 August 2007 at 2:10 PM
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.
8 August 2007 at 2:14 PM
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).
8 August 2007 at 2:20 PM
Re: #16, “According to the second law of th