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Convenient Untruths

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Gavin Schmidt and Michael Mann

Update 10/18/07: We are very disappointed that the Washington Post has declined to run an op-ed placing the alleged 9 ‘errors’ in a proper scientific context, despite having run an extremely misleading news article last week entitled “UK Judge Rules Gore’s Climate Film Has 9 Errors”.

Last week, a UK High Court judge rejected a call to restrict the showing of Al Gore’s An Inconvenient Truth (AIT) in British schools. The judge, Justice Burton found that “Al Gore’s presentation of the causes and likely effects of climate change in the film was broadly accurate” (which accords with our original assessment). There has been a lot of comment and controversy over this decision because of the judges commentary on 9 alleged “errors” (note the quotation marks!) in the movie’s description of the science. The judge referred to these as ‘errors’ in quotations precisely to emphasize that, while these were points that could be contested, it was not clear that they were actually errors (see Deltoid for more on that).

There are a number of points to be brought out here. First of all, “An Inconvenient Truth” was a movie and people expecting the same depth from a movie as from a scientific paper are setting an impossible standard. Secondly, the judge’s characterisation of the 9 points is substantially flawed. He appears to have put words in Gore’s mouth that would indeed have been wrong had they been said (but they weren’t). Finally, the judge was really ruling on how “Guidance Notes” for teachers should be provided to allow for more in depth discussion of these points in the classroom. This is something we wholehearted support – AIT is probably best used as a jumping off point for informed discussion, but it is not the final word. Indeed, the fourth IPCC report has come out in the meantime, and that has much more up-to-date and comprehensive discussions on all these points.

A number of discussions of the 9 points have already been posted (particularly at New Scientist and Michael Tobis’s wiki), and it is clear that the purported ‘errors’ are nothing of the sort. The (unofficial) transcript of the movie should be referred to if you have any doubts about this. It is however unsurprising that the usual climate change contrarians and critics would want to exploit this confusion for perhaps non-scientific reasons.

In the spirit of pushing forward the discussion, we have a brief set of guidance notes of our own for each of the 9 issues raised. These are not complete, and if additional pointers are noted in the comments, we’ll add them in here as we go along.

  • Ice-sheet driven sea level rise Gore correctly asserted that melting of Greenland or the West Antarctic ice sheet would raise sea levels 20ft (6 meters). In the movie, no timescale for that was specified, but lest you think that the 20 ft number is simply plucked out of thin air, you should note that this is about how much higher sea level was around 125,000 years ago during the last inter-glacial period. Then, global temperatures were only a degree or two warmer than today – and given that this is close to the minimum temperature rise we can expect in the future, that 20 ft is particularly relevant. The rate at which this is likely to happen is however highly uncertain as we have discussed previously.
  • Pacific island nations needing to evacuate Much of Tuvalu is only a few feet above sea level, and any sea level rise is going to impact them strongly. The impacts are felt in seemingly disconnected ways – increasing brine in groundwater, increasing damage and coastal erosion from tides and storm surges, but they are no less real for that. The government of Tuvalu has asked New Zealand to be ready to evacuate islanders if needed, and while currently only 75 people per year can potentially be resettled, this could change if the situation worsened.
    In the movie there is only one line that referred to this: “That’s why the citizens of these pacific nations have all had to evacuate to New Zealand”, which is out of context in the passage it’s in, but could be said to only be a little ahead of it’s time.
  • Climate impacts on the ocean conveyor The movie references the Younger Dryas event that occurred 11,000 years ago when, it is thought, a large discharge of fresh water into the North Atlantic disrupted the currents, causing significant regional cooling. That exact scenario can’t happen again, but similar processes are likely to occur. The primary unresolved scientific issue regards how quickly the circulation is likely to change as we move forward. The model simulations in the latest IPCC report show a slowdown in the circulation – by about 30% by 2100 – but there is much we don’t understand about modeling that circulation and future inputs of freshwater from the ice sheets, so few are willing to completely rule out the possibility of a more substantial change in the future. Further discussion on what this really means and doesn’t mean is available here and here.
  • CO2 and Temperature connections in the ice core record Gore stated that the greenhouse gas levels and temperature changes over ice age signals had a complex relationship but that they ‘fit’. Again, both of these statements are true. The complexity though is actually quite fascinating and warrants being further discussed by those interested in how the carbon cycle will react in the future. We’ve discussed the lead/lag issue previously. A full understanding of why CO2 changes in precisely the pattern that it does during ice ages is elusive, but among the most plausible explanations is that increased received solar radiation in the southern hemisphere due to changes in Earth’s orbital geometry warms the southern ocean, releasing CO2 into the atmosphere, which then leads to further warming through an enhanced greenhouse effect. Gore’s terse explanation of course does not mention such complexities, but the crux of his point–that the observed long-term relationship between CO2 and temperature in Antarctica supports our understanding of the warming impact of increased CO2 concentrations–is correct. Moreover, our knowledge of why CO2 is changing now (fossil fuel burning) is solid. We also know that CO2 is a greenhouse gas, and that the carbon cycle feedback is positive (increasing temperatures lead to increasing CO2 and CH4), implying that future changes in CO2 will be larger than we might anticipate.
  • Kilimanjaro Gore is on even more solid ground with Kilimanjaro. In the movie, the retreat of Kilimanjaro is not claimed to be purely due to global warming , but it is a legitimate example of the sort of thing one expects in a warmer world, and is consistent with what almost all other tropical mountain glaciers are doing. There is indeed some ongoing discussion in the literature as to whether or not the retreat of ice on Kilimanjaro is related to the direct effects (warming atmospheric temperatures) or indirect effects (altered patterns of humidity, cloud cover, and precipitation influencing Kilimanjaro’s ice mass) of climate change, and that argument isn’t yet over. But these arguments would be of more relevance if (a) we were not witnessing the imminent demise of an ice field that we know has existed for at least the past 12,000 years and (b) most of the other glaciers weren’t disappearing as well.
  • Drying up of Lake Chad It is undisputed that Lake Chad has indeed shrunk rapidly in recent decades. While irrigation and upstream water use are probably contributing factors, the dominant cause is the reduction of rainfall across the entire Sahel from the 1950s to the 1980s and with rainfall today still substantially below the high point 50 years ago. There is substantial evidence that at least a portion of this drying out is human-caused. A few recent papers (Held et al, PNAS; Chung and Ramanathan and Biasutti and Giannini) have addressed causes ranging from Indian Ocean changes in sea surface temperature to the increase in atmospheric aerosols in the Northern hemisphere. Gore uses this example to illustrate that there are droughts in some regions even while other areas are flooding. Unfortunately this is exactly what the models suggest will happen.
  • Hurricane Katrina and global warming Katrina is used in the film as a legitimate illustration of the destructive power of hurricanes, our inability to cope with natural disaster, and the kind of thing that could well get worse in a warmer world. Nowhere does Gore state that Katrina was caused by global warming. We discussed this attribution issue back in 2005, and what we said then still holds. Individual hurricanes cannot be attributed to global warming, but the statistics of hurricanes, in particular the maximum intensities attained by storms, may indeed be.
  • Impact of sea ice retreat on Polar bears As we presaged in August, summer Arctic sea ice shattered all records this year for the minimum extent. This was partially related to wind patterns favorable to ice export in the spring, but the long term trends are almost certainly related to the ongoing and dramatic warming in the Arctic. Polar bears do indeed depend on the sea ice to hunt for seals in the spring and summer, and so a disappearance of this ice is likely to impact them severely. The specific anecdote referred to in the movie came from observations of anomalous drownings of bears in 2004 and so was accurate. However, studying the regional populations of polar bears is not easy and assessing their prospects is tough. In the best observed populations such as in western Hudson Bay (Stirling and Parkinson, 2006), female polar bear weight is going down as the sea ice retreats over the last 25 years, and the FWS is considering an endangered species listing. However, it should be stated that in most of the discussions about polar bears, they are used as a representative species. Arctic ecosystems are changing on many different levels, but it is unsurprising that charismatic mega-fauna get more press than bivalves. In the end, it may be the smaller and less photogenic elements that have the biggest impact.
  • Impact of ocean warming on coral reefs Corals are under stress from a multitude of factors; overfishing, deliberate destruction, water pollution, sea level rise, ocean acidification and, finally, warming oceans. The comment in the movie that rising temperatures and other factors cause coral bleaching is undoubtedly true. Bleaching episodes happen when the coral is under stress, and many examples have been linked to anomalously warm ocean temperatures (Australia in 1998 and 2002, all over the Indian Ocean in recent years). Corals are a sobering example of how climate change exacerbates existing vulnerabilities in eco-systems, potentially playing the role of the straw that breaks the camel’s back in many instances.

Overall, our verdict is that the 9 points are not “errors” at all (with possibly one unwise choice of tense on the island evacuation point). But behind each of these issues lies some fascinating, and in some cases worrying, scientific findings and we can only applaud the prospect that more classroom discussions of these subjects may occur because of this court case.

492 Responses to “Convenient Untruths”

  1. 451
    Fred Staples says:

    Ray, I have been, and it hasn’t (449). I would consider it vulgar to have only one point of view on anything, Gavin.(447).

    I will not mention the second law again, if Barton will agree that the sun warms the earth and the earth warms the atmosphere, not the other way round. Obviously, any effect that inhibits cooling will allow the sun to warm the earth still further. (447).

    If we begin at the beginning with a bare rock, we can make sweeping assumptions and calculate a temperature of 255 degrees K. Now surround that rock with a thick layer of dense, low thermal conductivity gas which allows incoming heat to pass.

    The surface temperature will rise and the atmosphere will warm near the surface.


    [Response: Why? At equilibrium the surface energy balance only depends on exactly the same physics as the situation with no atmosphere. The rest of your post is just a litany of mis-representation and irrelevancies. Drive-by catalogues of supposed problems while never engaging on substance is pointless. Keep that for the newsgroups. – gavin]

  2. 452
    Marcus says:

    Fred, consider this: How does a thermos work? It uses a vacuum as an _insulator_. If I were to put a small heat source inside the thermos, it would eventually reach an equilibrium when the radiation out equals the heat input. Now, if I replace the vacuum in the thermos with a gas, does the inside heat up? No. If anything, the inside cools down, because now you have another method for transferring heat away.

    In your planetary example, the low thermal conductivity gas will conduct some amount of heat away from the surface, but since the gas itself is surrounded by a vacuum, it won’t serve for significant cooling. But if the sign is in any direction, it is negative, not positive, since it hasn’t impeded the radiative flow out (the planet’s only mode of cooling before), only added a new cooling mode.

  3. 453
    Ray Ladbury says:

    Yes, Fred, we all know that pretty much all the heat that warms Earth comes from Mr. Sun. We also know that all the energy that leaves Earth must do so as LWIR. However, once energy leaves the surface, the portion of it that is trapped by ghg absorption, etc. is most easily viewed as a new source of energy. After all, you do have IR and thermal energy that goes into heating the atmosphere and surface. No one is violating any physical laws, Fred. So if you have a specific objection, state it clearly. If you have not worked it out clearly enough to state it clearly, go do so and come back, or try to enunciate what is bothering you and we’ll try to help you work through it.

  4. 454
    Figen Mekik says:

    “I would consider it vulgar to have only one point of view on anything”

    Really? That’s a dangerous blanket statement for science.. Wouldn’t you really consider your doctor incompetent if he said “well you might live or you might die, it’s all relative.” Multiple points of view on the same subject is for lawyers who make a living with creating “the reality” that suits their client’s needs the best. A scientist can’t say “you can interpret the data this way or maybe that way,” and then pick the version that advances some preconceived notion or agenda the scientist has. While there may be multiple ways of interpreting observations, a scientist has the responsibility to present the one explanation that best fits all the data (not just the convenient, cherry picked ones). Can’t waffle much, or you aren’t doing science any more.

  5. 455

    Fred posts:

    [[I will not mention the second law again, if Barton will agree that the sun warms the earth and the earth warms the atmosphere, not the other way round]]

    The sun warms the Earth. The Earth warms the atmosphere. And the atmosphere warms the Earth.

    No, I won’t agree to a falsehood, or to an incomplete truth which gives a misleading picture. The Earth gets a great deal of infrared radiation from the atmosphere. We’ve measured it.

  6. 456
    Fred Staples says:

    Marcus,(452)don’t forget the reflector in the thermos. Take that away and radiation losses would increase dramatically, and your source would cool. The radiative energy is proportional to the difference between the fourth powers of the temperatures in degrees K – source to room. Put low thermal conductivity gas into the vacuum and its inner surface temperature would rise towards that of your source. The radiation losses would fall dramatically, (that fourth power), and the source would warm again.

    My bare rock is radiating to space, near zero temperature. The atmospheric gas blanket works just like a conventional blanket (warmer on the inside), and the surface heats. The atmosphere conducts, convects, (and from the sea evaporates) the heat away, and reduces the radiative loss (negligible in the troposphere). At the top of the atmosphere the heat radiates to space (fourth powers again).

    Into that simple model, Ray wants to introduce “a new source of energy”, but he does not really mean that. He means that the water vapour, CO2 et al will absorb radiation, increase the troposphere temperature and reduce the radiative heat loss, so warming the surface still further.

    In a greenhouse you get much the same effect, with the glass taking the place of the atmosphere. I have calculated elsewhere the 18.9% increase you could expect in the interior. Sadly, there is no sign of it, and greenhouse design does not it into account (Google casts a wide net).

    So, Ray I will repeat my original question, and then go away and think about entropy (I worked in Atomic Power stations, so I know something about waste heat, sources, and sinks).

    Of the 33 degree increase in temperature between the surface and the tropopause, how much can be attributed to the greenhouse gasses?

    And one more thing, 454, I thought it might be useful to introduce a note of scepticism into this otherwise excellent web site.

  7. 457
    Marcus says:

    Fred: If your gas is transparent in the wavelengths of the radiation, then the bare rock of the planet is still radiating to space, and therefore radiation loss DOES NOT CHANGE. What _does_ change is that you’ve added the possibility for convective heat loss as well as radiative heat loss.

    If your gas _isn’t_ transparent in the wavelengths that the rock is radiating in, then your gas is a greenhouse gas.

    Yes, the reflector in a thermos improves its insulative properties, but even without the reflective layer a double layered glass bottle with vacuum in between the two layers makes a better insulator than one with air in between the two layers.

  8. 458
    Hank Roberts says:

    So is your analogy here
    — the reflector in the thermos is acting somewhat like the greenhouse gases in the atmosphere, sending heat energy back down toward the middle?

  9. 459

    Fred posts:

    [[Of the 33 degree increase in temperature between the surface and the tropopause, how much can be attributed to the greenhouse gasses?]]

    All of it.

  10. 460
    Blloper says:

    #41, the reason that there are locks in the Panama Canal is due to the topographical differences in the country (often referred to as the Continental Divide).

  11. 461
    Fred Staples says:

    Thank you , Barton (459).

    Of a 10 degree increase between the interior and the exterior of a greenhouse, how much can be attributed to radiative effects from the glass?. (In our globally warmed UK climate, I spend a great deal of my time in a glass conservatory, and the interior surface of the glass is warmer than the exterior, but not as warm as the interior atmosphere).

  12. 462
    Ray Ladbury says:

    The atmospheric greenhouse effect has little to do with the way a real greenhouse works. So the first thing you need to do is get that model out of your mind. Then go find a good text on atmospheric radiation and learn the real physics.

  13. 463
    Fred Staples says:

    I have done that, Ray,(to some extent anyway)and I remain sceptical. We both know that neither a greenhouse interior nor the earth’s surface is warmed by back radiation, although there are many examples on the internet of people who think the opposite. The single slab model, after all, is the same for both: W in, 2W from the interior/surface, W back from the glass/atmosphere, W out – temperature ratio increase the fourth root of two. Until Mr Woods’ experiment ( and for at least 50 years afterwards) that was conventional wisdom.

    We both know that the explanation for a real greenhouse is convection inhibition, and the only possible explanation for atmospheric greenhouse is the “higher is cooler” effect whereby the inhibition of surface radiation moves the radiant point to space to a higher/colder level, and the necessary warming increases all the lapse rate temperatures, including the surface.

    That is plausible, but is it true? After all, inhibiting radiation implies energy absorption which will be rapidly disseminated and should differentially increase the troposphere temperatures over the surface temperatures. I do not see that effect in the satellite measurements. Is there any land-based experimental evidence?

  14. 464
    Ray Ladbury says:

    Actually, yes, the surface is warmed by back radiation–or you can look on it as the net radiation away from the surface decreasing–they are equivalent. And yes, the troposphere is warmed. Even the UAH group concede this now. Land based experimental evidence? Looked at the GISS results? Have you looked at the inferred temperatures in the CO2 band? That there is warming is beyond question. That we have a physical mechanism that explains it both quantitatively and qualitatively is also beyond question. Beyond this, I’m not sure what kind of evidence you could be looking for.

  15. 465

    [[ We both know that neither a greenhouse interior nor the earth’s surface is warmed by back radiation]]

    No matter how many times you repeat this, it still won’t be true. The Earth receives 324 watts per square meter, on the average, of back radiation from the atmosphere. We’ve measured it with instruments. It’s there. Deal with it.

  16. 466
    David B. Benson says:

    Fred — Have you read the AIP Discovery of Global Warming pages, linked in the Science section of the sidebar?

  17. 467
    Fred Staples says:

    My reply to 464 has been delayed by a holiday in Venice (height above sea level two or three feet for the last 800 years or so). The two explanations are not equivalent, Ray. One is sensible and the other (because it ignores energy quality) isn’t.

    The sensible explanation has consequences which can be tested. If back radiation from increased “greenhouse” gasses in the troposphere is responsible for a 0.75 degree centigrade rise in temperature at the surface, the troposphere temperature increase must be greater. The troposphere increase can be estimated from the Stefan-Bolzmann fourth power law, and is about one-third of a degree higher.

    No data I have seen shows that differential increase. Houghton (Global Warming, The Complete Briefing, Third Edition, Page 59) states “The trend in the difference of the surface and lower troposphere of 0.13 +- 0.06 degrees centigrade per decade is statistically significant.”

    Sadly, it is in the wrong direction.

  18. 468
    Ray Ladbury says:

    Fred, you don’t have the foggiest notion of what you are talking about. Is energy being absorbed by the greenhouse gasses? (definitely yes) If so, what happens to it? (most of it goes into kinetic energy via collisions with atmospheric gasses; some goes into radiation; however, it can’t leave the system via any mechanism other than radiation) Is the energy absorbed sufficient to account for the warming seen? (Yes) It’s pretty simple, Fred. Once the energy gets trapped on its way out of the system, it can’t get out until the entire climate warms enough so that the atmosphere above the trapping layer is warm enough to radiate away the difference.

  19. 469
    Fred Staples says:

    Yes, David (466), I have.

    Yes, I have. He presents most of the standard objections to AGW and then attempts to demolish them. He suggests that looking at the atmosphere as a series of interacting layers, rather than a single slab, and a minute change of greenhouse gas concentration in the upper layers will perturb the entire system.

    He states that the warming which took place up to 1940 was probably not due to CO2, which had not increased significantly. (Actually, that bitterly cold period was the previous temperature peak between the Little Ice Age and the current warming)

    He quotes Vostok to suggest that temperature and CO2 had always been closely correlated. He mentions that, during past glacial periods, temperature changes had preceded CO2 increases by several centuries (not the other way round). He faces the problem squarely, and passes on.

    He asserts that the warming “since the 1980’s” was unprecedented (it was not) and “scarcely any reputable expert doubted that greenhouse gasses were at least partly responsible”. (Did any reputable expert think they weer wholly responsible)

    His quotes two crucial observations to confirm the AGW theory: first, sea temperatures up to 2005 were rising with a temperature distribution predicted by the AGW models, and second, the rate of heating was caused by a radiation imbalance – the earth was receiving more energy than it was radiating (James Hansen’s smoking gun).

    Sadly, since the essay, the iron law of confident assertions has come into play. CO2 has continued to rise faster than ever (along James Hansen’s A line), global temperatures from 1998 ceased to increase (the Hansen C line corresponding to constant emissions) and the sea temperatures ceased to warm.

    [Response: Not so. Why make claims that are so easily shown to be wrong? The current net forcings are slightly lower than the B scenario (see ). – gavin]

  20. 470
    Fred Staples says:

    I will check that link, Gavin, but if the CO2 and temperature lines continue to diverge, the AGW theory will get into trouble, because the models follow the CO2.

    In the meantime I have been comparing and contrasting Ray Pierrehumberts excellent on-line account with the G and T paper. Ray’s first mention of thermal conductivity is in section 8, G and T’s in section 1. As Churchill said “they will never agree. They are arguing from different premises”.

    Ray’s “greenhouse in a nutshell” is the clearest “higher is colder” explanation I have found, and this theory is the only plausible explanation of AGW.

    He says
    “As more greenhouse gas is added to an atmosphere, more of the lower parts of the atmosphere become opaque to infrared, preventing the escape of infrared radiation from those regions. This increases the altitude of the effective radiating level (i.e.decreases prad).” And
    “. It is very important to recognize that greenhouse warming relies on the decrease of atmospheric temperature with height, which is generally due to the adiabatic profile established by convection. The greenhouse effect works by allowing a planet to radiate at a temperature colder than the surface, but for this to be possible, there must be some cold air aloft for the greenhouse gas to work with.”

    If we accept these ideas we have a warmer lower atmosphere triggering the entire “greenhouse” effect. The clear implication is that AGW starts in the atmosphere, heat is trapped, and the atmosphere will warm more than the surface.

    The evidence (467) is in the opposite direction – since 1979 the surface has warmed more than the atmosphere

    The entropy argument is worth stating to deal with the notion that the atmosphere could warm the surface directly. Suppose a section of the atmosphere at a temperature Ta absorbs OLR, and radiates energy deltaQ in the form of heat to earth. If the earth absorbs the heat at a temperature Ts, the change in entropy is –deltaQ/Ta + deltaQ/Ts. But that means that the overall entropy will decrease spontaneously, (the negative ratio is greater than the positive) because the surface temperature is higher than the atmospheric temperature.

    And that, Barton, (465) is impossible. To put the second law more technically, however long you stand there, and however hot it gets, your bum is not going to warm that fire.

    There is another implication of “higher is colder”. If the lapse rate is necessary for greenhouse gasses to have any effect, how can we attribute the 33 degree atmospheric temperature increase entirely to the greenhouse gasses?

    [Response: It’s certainly true that without a lapse rate there is no greenhouse effect. But there is always a lapse rate and would be even in the absence of GHGs. – gavin]

  21. 471
    Hank Roberts says:

    Fred, you’ve written above:

    > (Did any reputable expert think they weer wholly responsible)

    and a few postings later you write

    > how can we attribute the 33 degree atmospheric temperature
    > increase entirely to the greenhouse gasses?

    You sound confused.

  22. 472

    Fred Staples (#470) wrote:

    If we accept these ideas we have a warmer lower atmosphere triggering the entire “greenhouse” effect. The clear implication is that AGW starts in the atmosphere, heat is trapped, and the atmosphere will warm more than the surface.

    Strangely enough, I dealt with this briefly yesterday:

    Anyway, if people want to see the effects of the different greenhouse gases in terms of the cooling or warming of the atmosphere at various altitudes, I would suggest:

    Radiation & Climate: Major Projects
    Line-by-line calculation of atmospheric fluxes and cooling rates 2

    They will notice that the direct effect of carbon dioxide is principally one of cooling the atmosphere, not warming it. This is because the radiation which is emitted by carbon dioxide has on the balance the effect of cooling the atmosphere (due to emitting backradiation to the surface and thermal radiation to space) but warming the surface — with the troposphere being warmed principally by thermals and evapotranspiration.

    24 November 2007 at 3:41 AM
    Comment 354 to Post BBC contrarian top 10

    Odd how often that sort of thing happens.


    Fred Staples (#470) wrote:

    The entropy argument is worth stating to deal with the notion that the atmosphere could warm the surface directly. Suppose a section of the atmosphere at a temperature Ta absorbs OLR, and radiates energy deltaQ…

    The surface emits the thermal radiation first – after absorbing sunlight. This in essence warms the atmosphere (assuming you are considering vibrational, rotational and rovibrational states as a form of temperature) by emitting thermal radiation – prior to the atmosphere emitting thermal radiation. And even a cool blanket will reduce the chill if it is warmer than the night air. It slows the loss of heat. I do trust that insolation isn’t a violation of the second law of thermodynamics?

    If energy continues to enter the system at the same rate with a diminished rate at which it is lost to the environment, things tend to heat up. This follows from the first law of thermodynamics. But I prefer to think of it as simply the conservation of energy.


    Just out of curiosity, do you actually think that the second law of thermodynamics somehow slipped the minds of the entire profession of climatologists?

  23. 473
    Lawrence Coleman says:

    re: Ray..Follows the ol adage that “there are none so blind than those who do NOT WISH to see” Some people are just born contrarians for the sheer hell of it. no matter how serious the issue is they will always seek a contrarian approach. They will be the ones still smoking 3 packs/day because they do not believe it leads to lung cancer; they will gorge themselves silly on big macs because they refuse to accept that it leads to heart disease and diabetes; I’m pretty sure they still belive with absolute conviction that the earth is flat. Sorry Ray, they will learn the hard way..we rather would prefer to stand on the shoulders of giants.

  24. 474
    Nick Gotts says:

    Re #473 (Lawrence Coleman) “Sorry Ray, they will learn the hard way..we rather would prefer to stand on the shoulders of giants.”

    Particularly if Hansen’s concern about rapid sea-level rise turns out to be justified :-)

  25. 475
    Tarab says:

    Hello webmaster…Thanks for the nice read, keep up the interesting posts..what a nice Tuesday

  26. 476
    Fred Staples says:

    Confused (471), quite possibly.

    Take, for example, Gavin’s link (469) on the Hansen scenarios. Hansen’s original paper in August, 1988 states: “Specifically, in scenario A CO2 increases as observed by Keeling for the interval 1958 – 1981 and subsequently with 1.5% per year growth in the annual increment”. Maddeningly, he does not quote the Keeling figure, but the Keeling curve gives about 25 ppm in 23 years, or 1.087 ppm per year.

    His B scenario starts at the same rate and increment, but the increment falls to 1% per annum in 1990, 0.5% in year 2000, and zero in 2010. He quotes the annual increment after 2010 as 1.9 ppm pa, which means that scenario B must have started at 1.59ppm pa in 1988.

    If we use the 1.59 ppm increment (approximately 1965 to 1978 on the Keeling curve), the projected CO2 level in 2006 is Scenario A 384 ppm, Scenario B 383 ppm, and the actual is 382 ppm.

    We are, consequently close to scenario B for emissions, although the current rate of increase is above 1.9 ppm per year.

    For the temperatures, there is an excellent plot in Gavin’s link, the Global Monthly Mean Surface Temperature Change from 1997 to date. Looking at that chart, can anyone see a temperature increase between 1998 and today?

    For UK data alone, the annual average reached 10.53 degree C in 1997, and the ten year average is now 10.30. The GISS global data show no increase since 1997.

    The satellite data is also similar. UAH has not moved since 2001 and peaked in 1998. RSSMU is similar, but is currently falling sharply, almost a full degree below the 1998 peak. The Hadley CRUT3 data peaked in 1998, and has fallen back since.

    The radiosonde data peaked in 1998, fell back, and has been more or less constant since.

    So, are the CO2 emissions and the temperature increases diverging, and if this continues what will happen to the AGW theory?.

    We have an abundance of recent temperature data. In the pre-satellite era the most reliable must be the radiosondes, and the US and UK surface air temperature records. The US data shows that the 1980 – 2000 temperatures (and increases) are little different from the 1910 – 1930 data. Certainly not sufficiently different to cause alarm.

    In the UK, the warmest years in the record were 1990 and 1999, at 10.63 degrees centigrade, and in only 39 of the 347 years was the average temperature between 10.0 degrees and 11 degrees C. Of these relatively warm years, 20 occurred before 1945.

    As for the second law,(472) you are more conscious of it if you have worked on(nuclear) power stations (have you ever wondered what the cooling towers are for) and low (towards absolute zero) temperature physics?. I agree about the cooling blanket effect. That is the alternative (terrestial greenhouse) view of this entire subject (see the G and T paper, which starts with the low thermal conductivity of air).

    I would like to give more thought to Gavin’s lapse rate comment (470), which I think gets to the heart of the matter.

  27. 477
    Ray Ladbury says:

    Fred, OK, you agree that a CO2 molecule will absorb outgoing LWIR, right? Now the vast majority of CO2 molecules so excited, will relax collisionally, rather than radiatively, due to the relatively long life of the excited state. So, where does all that energy go? It cannot escape the climate system except as LWIR, correct? If a CO2 molecule emits a LWIR photon at low altitude, it will likely be absorbed by another CO2 molecule, right? So the only way for the extra energy to escape is for the entire atmosphere to heat up enough for there to be increased radiation from high in the atmosphere. Net effect: global warming.
    You claim there has been no warming since 1998. Well, 1998 was a very deep El Nino. 2007 is a La Nina year. The trend is still UP. You claim that we should not be concerned about warming because the rate of increase is comparable to the period 1910-1930. Absolute temperature matters, Fred. The warming trend is not stopping or even slowing.

    Fred, I would suggest that you start worrying about all the laws of thermo–not just the 2nd, which you don’t understand. The net flux of energy is still from warm to cold–it’s just that the net flux is decreased.

  28. 478
    Fred Staples says:

    First, Ray, there is no extra energy. There are no energy-generating reactions in the atmosphere.

    To explain what happens in the atmosphere in terms of light particle models (photons) is asking for trouble. That form of analysis is essential for neutrons in reactors, where capture cross sections and mean free paths in fuel and moderator determine the reactor design. It has little to contribute to atmospheric physics where we are dealing with electro-magnetic radiation, sensible heat transmission, and resonant absorption by diatomic and triatomic molecules. Both will absorb and radiate, Ray, both will transfer kinetic energy. Nitrogen and Oxygen are much less effective, but far more numerous. As far as I know, the only electron shell excitation occurs in the diatomic molecules, excited by the high energy incoming radiation.

    You use the Stefan-Bolzmann equations for energy transfer, and neither of those distinguished gentlemen knew anything about the structure of an atom. (Have you ever looked at the original explanations for the interior of a black-body)?

    The energy absorbed by additional CO2 increases the efficiency of heat transfer from the surface. What will that do to the surface temperature? (G and T’s pot on the stove analogy is worth thinking about).

    I agree that the atmosphere will warm (marginally) if the CO2 concentration increases. The rest of your post begs all the questions “So the only way for the extra energy to escape is for the entire atmosphere to heat up enough for there to be increased radiation from high in the atmosphere. Net effect: global warming”

    How? Why? The atmosphere radiated the energy into space before the CO2 increase – it will do so after. It will choose its own height to balance the incoming and outgoing energy.

    The notion of the surface and atmosphere radiating against each other, diminishing the surface output, is something we have discussed several times. It is plausible, but the radiation laws require the atmosphere to heat more than the surface. This could happen, of course, but the measurements show that it doesn’t. (Exactly as the back radiation from the glass could increase the temperature of a greenhouse interior – it could, but it doesn’t).

    We are left with Ray Pierrehumbert’s higher is colder argument, “more of the lower parts of the atmosphere become opaque to infrared, preventing the escape of infrared radiation from those regions. This increases the altitude of the effective radiating level” to a level which is colder (the lapse rate), and which creates an energy imbalance. Consequently, both earth and atmosphere are warmed.

    This is the only explanation possible, and it is plausible if there is any evidence for the “opaque to infrared” notion, and if the atmosphere warms at least as much as the surface. Is there and does it?

  29. 479
    Fred Staples says:

    You mentioned that “absolute temperatures matter” in you response to my comments in 476, Ray.

    Have you seen the NASAGISS data at

    The annual and five year peaks in the early thirties are very close to the past decade. One of the annual averages is warmer than the El Nino enhanced 1998.

    In the UK, 1949 was the fourth warmest year since 1649, behind 1990, 1999, and 2006, but well ahead of 2007, (1998 is 19th warmest)

    The author of the link quotes some interesting correlations with CO2 levels. From 1895 to 2006 the r squared correlation is just 0.29.Given that the CO2 increase and the little ice-age recovery coincided, this does not suggest CO2 as a significant cause.

    For the last decade, with flat temperatures and increasing CO2, the correlation is negligible. Granted, ten years is too short a period to prove anything, but if this trend continues for another ten years the IPCC trend rate of 0.2 degrees per decade will demonstrably not be there. Objectively, Ray, it is very hard to say that the “the warming trend is not stopping or even slowing” and “the trend is still UP”.

    Twenty years without an increase will be the same elapsed time as the 1978 – 1998 increase on which the whole AGW theory depends.

    [Response: … and if the moon was made of green cheese…. Look, the issue is that our physical understanding of the system implies that continued high emissions of CO2 (and other forcings) will cause wamring over the next few decades of around 0.2-0.3 deg C/dec. If you have a physical model, or statistical fit, or anything other than your gut feeling, that predicts something else, publish it, and we will see how well it fits what has already happened and eventually how your projection works out. If you are convinced that we are all wrong, why don’t you bet James Annan or Brian Schmidt that it will cool? They’ll even give you favorable odds. – gavin]

  30. 480
    Ray Ladbury says:

    Fred, brace yourself. The world is not the UK. Yes, Fred, there is a whole world out there, and it would seem that that world is warming. We can tell that by rising temperatures; we can tell it by melting ice; we can tell it by the fact the winters are shortening and nights are getting warmer. The past 20 years have had 13 of the warmest in the past 130 years. A warming world doesn’t mean we will get warmer every year, and CO2 is not the only forcer, but it is a forcer, and I’ve always found physics to work pretty well.

  31. 481
    Gary Moran says:

    I feel somewhat for Fred on this one, having spent the last 48 hours going through the same routine. I’m pretty sure that the issue here is semantics. Back radiation from the atmosphere cannot directly heat the surface, that would be a violation of the 2nd law of thermo. However the radiation equilibrium explanation of the atmospheric effect is a long period average, and as such the raising of surface temperature is due to a slow down of heat loss from the surface over time not a direct heating, can someone confirm that this is correct, remember it may ease Fred’s pain. Thanks.

  32. 482
    Ray Ladbury says:

    Gary, It’s really a distinction without a difference. Yes, you can look at it as a change in the net energy flow. On the other hand, the excited GHGs really do radiate and relax collisionally, so you can also view that as a source term. Ask yourself how Earth would behave in the absence of GHGs. Now add them in, and the difference is the forcing of the GHGs. Remember, the 2nd Law (stat mech version) does not say that energy never flows from low temperature to high, just that it is favored (NET) to go the opposite way.

  33. 483
    Phil. Felton says:

    Re #481

    “Back radiation from the atmosphere cannot directly heat the surface, that would be a violation of the 2nd law of thermo.”

    Nonsense, it’s the basis of radiative heat transfer!

    I’m sure you’re aware that the radiative heat loss from the earth (Te) with an absorbing atmosphere (Ta) will depend on (Te^4-Ta^4) the second term is due to the back radiation from the atmosphere. If the atmosphere is transparent to IR then the term becomes (Te^4-4^4). No violation of the second law here.

  34. 484
    Gary Moran says:

    RE: 482 & 483

    thank you for your responses.

    I know that 2nd law doesn’t prevent proscribe transfer from cool to warm, just that the net flow must go from warm to cool. Comment 482 is comforting because it supports that; comment 483 is more troubling.


    To be clear when I say back radiation can’t heat the surface, I don’t mean the atmosphere can’t radiate energy to the surface, just that in the energy exchange between the atmosphere and the surface that the surface loses more energy than it gains. Any rise in surface temperature is an average rise because the thermal gradient is reduced. Any problems there with my understanding?

  35. 485
    Hank Roberts says:

    Gary, this statement is oddly familiar, I’ve seen it repeatedly, but I don’t recall this stated as a generalization by one of the climate scientists. What’s your basis for bringing it up? Do you have a reference somewhere on this subject you’re quoting from or reading?

    There’s no abstract average ‘surface’ — there’s dirt, water, green grass, snow, dry leaves. The air temperature around them changes.
    What point are you getting at? And is there a way to test it that could prove it wrong?

  36. 486
    Phil. Felton says:

    “comment 483 is more troubling.
    To be clear when I say back radiation can’t heat the surface, I don’t mean the atmosphere can’t radiate energy to the surface, just that in the energy exchange between the atmosphere and the surface that the surface loses more energy than it gains. Any rise in surface temperature is an average rise because the thermal gradient is reduced. Any problems there with my understanding?”

    Thermal gradients aren’t relevant to radiation heat transfer. A cooling surface does lose more heat than it gains but the net loss depends on the amount ‘back radiated’ as explicitly stated in 483 (not sure why that’s troubling?) In the context of a transparent atmosphere at night the loss is high because the back radiation (∝4^4) is essentially zero, with an absorbing atmosphere at say 250K the back radiation is much higher and the surface will cool much less rapidly. In the case of a cold surface when a warm front moves through and the atmosphere is warm and moist it’s possible that the surface will heat up!

    It’s ok to talk in terms of ‘net transfer of heat’ in the context of the 2nd law but it’s incorrect to say that heating by back radiation violates the 2nd law.
    Consider the following experiment:

    You have a surface at T1 in equilibrium with a cold surface above it, T2, (T2 less than T1). Above that surface you have yet another surface at T3 (T1 greater than T3 greater than T2), remove the middle surface and T1 increases. (do it in vacuum if you want to eliminate convection).
    By the way how can I display mathematical symbols (e.g. less than) on this blog?

  37. 487

    Gary Moran (#484) wrote:

    To be clear when I say back radiation can’t heat the surface, I don’t mean the atmosphere can’t radiate energy to the surface, just that in the energy exchange between the atmosphere and the surface that the surface loses more energy than it gains. Any rise in surface temperature is an average rise because the thermal gradient is reduced. Any problems there with my understanding?

    I will take a stab at this. However, I should point out that I am a philosophy major turned computer programmer. But oddly enough, my lack of expertise might come in handy at this point — since I can share a problem or two that I have had — and their resolution.


    You write, “To be clear when I say backradiation can’t heat the surface, I don’t mean the atmosphere can’t radiate energy to the surface…”

    I understand what you are saying – the net energy transfer between the surface and the atmosphere has to be from what is warmer to what is cooler. But strictly speaking, backradiation heats the surface when it is absorbed because radiation which is absorbed heats that which it is absorbed by. When we speak of backradiation, we are specifically focusing on the radiation which is emitted by the atmosphere and absorbed by the surface.


    Anyway, it might help to keep in mind that there are a fair number of energy transfers taking place — and radiation is just part of the picture.

    Please see:

    Earth’s energy budget diagram. Incoming sunlight is on the left; outgoing infrared or “longwave” radiation is on the right.
    Credits: From Kiehl, J. T. and Trenberth, K. E. (1997). “Earth’s Annual Global Mean Energy Budget”. Bulletin of the American Meteorological Association 78: 197-208.

    … which I got from:

    Global Warming, Clouds, and Albedo: Feedback Loops

    This diagram might help in part because it is showing that thermal energy enters the atmosphere not simply by means of radiation, but also by means of thermals and latent heat. They are part of the equation.


    You will notice that the majority of radiation which the atmosphere emits is in fact backradiation — with 324 W/m2 going to the surface but only 165 W/m2 going to space. This seemed puzzling to me, since the radiation which the atmosphere emits should show no preference with respect to direction.

    But as far as this diagram goes, it isn’t showing all of the absorptions and emissions which are taking place within the atmosphere itself. So while radiation which is emitted by the atmosphere from somewhere inside the atmosphere will show no preference for direction, this actually says very little about the final step where the radiation leaves the atmosphere either by being absorbed at the surface or escaping to space.

    This becomes particularly important when one considers the fact that most of the radiation which is absorbed by the atmosphere is actually thermal radiation which was emitted by the surface. Shortwave, visible sunlight is absorbed by the surface then reemitted as longwave thermal radiation. The atmosphere is thicker nearer the surface, so the energy won’t make it very far before it is absorbed by the atmosphere.

    Taking a random walk involving absorptions and emissions, it is more likely to make it back to the surface than to space — at least just after it has been emitted by the surface — since the optical thickness of the path to the surface will generally be much shorter than the optical thickness of the path to space (where by “optical thickness,” we are taking into account not just the distance, but the degree to which the atmosphere is opaque to radiation).


    You write, “… just that in the energy exchange between the atmosphere and the surface that the surface loses more energy than it gains…”

    This is problematic.

    First, at equilibrium, the surface is neither gaining nor losing energy. So the real question is, “What shifts the equilibrium?” An atmosphere that becomes more opaque to thermal radiation will shift that equilibrium because it will reduce the rate at which thermal radiation is lost to space, requiring the surface to warm up so that the rate at which it emits radiation will increase enough that it will compensate for the increased opacity of the atmosphere — such that once the new equilibrium is achieved, the rate at which (thermal) energy enters the climate system equals the rate at which (thermal) energy leaves the climate system.


    You write, “Any rise in surface temperature is an average rise because the thermal gradient is reduced.”

    There would seem to be an initial (“instantaneous”?) drop in thermal gradient – as the increased opacity of the atmosphere near the ground must result in more absorption of radiation by the atmosphere, raising the temperature at that level, but I am not sure how helpful this will be in terms of understanding the process. In fact, as the atmosphere becomes opaque in the lower troposphere, this will actually lower the temperature in the stratosphere as less thermal radiation is able to make it to the stratosphere — until the surface warms sufficiently to compensate for the increased opacity of the troposphere.


    Despite its complexity, the greenhouse effect is well-understood, and not simply in terms of theory but detailed measurements. (“Well-understood” by the experts at least — my own understanding is a work in progress.)

    We are able to image the reemission of thermal radiation by the atmosphere at various wavelengths and at various altitudes using satellites, measure the concentrations of different greenhouse gases and even measure the altitude of land by means of the optical thickness of the atmosphere at a given wavelength. In fact, we are able to image concentrations of carbon dioxide at 8 km by means of the thermal radiation it emits — and see higher concentrations of carbon dioxide rising up from the more heavily populated coasts of the United States than from the surrounding areas.

    Please see:

    NASA AIRS Mid-Tropospheric (8km) Carbon Dioxide
    July 2003

    In fact, using the spectral data that the satellites collect from the thermal radiation, we are able to create animations showing the various processes which are at work in the atmosphere.

    Please see:

    AIRS > Multimedia > Animations

    … not that we are entirely dependent upon satellites for this sort of data — we are also able to measure the increase in infrared radiation at the surface — such as when water at the tropics rises above 85 F, and backradiation from “clear skies” water vapor tends to more quickly than the thermal radiation from the surface.

    For example:

    Observations in the tropical Atlantic ocean (11) show that the clear sky downwelling infrared flux incident on the surface (Fa) also increases faster than the surface emission with increasing SST. The net result is further warming of the surface, which in turn induces additional heating of the atmosphere column above.

    Direct radiometric observations of the water vapor greenhouse effect over the equatorial Pacific Ocean
    F.P.J. Valero, W.D. Collins, P. Pilewskie, A. Bucholtz, and P.J. Flatau
    Science, 274(5307), 1773-1776, 21 March 1997

    Anyway, I hope this helps.

  38. 488
    Hank Roberts says:

    Ah, never mind Gary. I found where you’re discussing this at CA.
    Did you notice McI said there: “The problem with the thermodynamic discussions is not that they are dissenting “opinions” but that they tend to be “opinions”….” It’s hard to get to the science.

  39. 489
    Hank Roberts says:

    And this ought to wrap up the thermodynamics — an invitation from Dr. Curry to readers (at CA) to pose specific questions, after they’ve read her textbook on the subject. Good reading:

  40. 490
    Gary Moran says:

    thank you all for your time and effort on this.

  41. 491
    Ray Ladbury says:

    Gary, I don’t know if this will help you, but the way I think of it is this: Matter tends to radiate roughly with a blackbody spectrum. So where does the blackbody spectrum come from? It is the equilibrium distribution of a photon gas. However, photons don’t interact with each other, so the only way the photon gas can come to equilibrium is by interacting with the matter around it. Thus, the photons wind up (more or less) in thermal equilibrium with the matter around them as well. Since no matter is a perfect absorber, the photon gas can only interact with the matter in those wave bands where the matter can absorb photons.
    In the IR spectrum where Earth radiates thermally, most gasses are inert. It’s only the greenhouse gasses that can absorb photons and modify the photon spectrum. Since temperature decreases as you go up in the atmosphere, it makes sense that in the greenhouse IR absorption bands, the photons emitted must be at a lower temperature than the noninteracting photons. In fact at low altitudes, most excited ghg molecules don’t re-emit photons at all, but rather relax collisionally. So if we look at Earth from space in the CO2 band, we see radiation at a much lower temperature than if we look well away from that band, because the IR photons only manage to escape if they originate high in the troposphere or lower stratosphere.

  42. 492

    Gary (490),

    I don’t know how much I might have helped you, but just to let you know, you helped make certain things a little more clear to me.

    The way in which I had been thinking of the greenhouse effect was that by raising the level of carbon dioxide in the atmosphere, one increases the opacity of the atmosphere to thermal radiation. Infrared absorbed by carbon dioxide is emitted, with much of it being absorbed by the surface leading to moist air convection which in turn warms the atmosphere. In fact, this is the essential process as I have described it a number of times on the blog.

    However, what didn’t fully click for me was the fact that when thermal radiation from the surface is absorbed by carbon dioxide, it is warming the atmosphere. So even at this stage, the atmosphere is being warmed — prior to thermals or moist air convection — prior to even the additional warming of the surface itself. I think part of the problem for me was that I was still holding on to a false dichotomy between line radiation and blackbody radiation — where I was thinking of blackbody radiation as thermal radiation but was failing to fully think of the line radiation emitted by greenhouse gases as thermal radiation.

    But thermal radiation is generally somewhere in between. There are no perfect black bodies, and line/band-radiation is always somewhat spreadout. And the thermal radiation of the atmosphere itself (with numerous gases) is actually already beginning to look a lot like black body radiation, a great deal more so at least than the spectra of a single gas. Additionally, viewing it in the way is more of a piece when you get into vibrational, rotational and rovibrational temperatures a little further on when analyzing the greenhouse effect in terms of radiation transfer theory and the underlying quantum mechanics, that is, quantized states of molecular excitation.

    Now at least in what is called a local thermodynamic equilibrium (generally at pressures of 10 mb or above), there will be a million or more collisions for any molecule per half-life of any of the relevant excited states. As such, the collisions will bring these exotic vibrational, rotational and rovibrational temperatures into equilibrium with the the translational temperature — in much the same way that different gases in the same parcel of atmosphere will be the same temperature. In fact, this is essentially what we mean by local thermodynamic equilibrium — that the Planck-Boltzmann temperature of the radiation which interacts with the atmosphere is the same as the Maxwell temperature of the matter with which it interacts.

    As such, when the radiation gets absorbed by the atmosphere, it is thermalized — quickly lost by the individual molecules to the surrounding atmosphere by molecular collisions. However, what greenhouse gases lose to molecular collisions they may also gain by molecular collisions. CO2 and water vapor will lose energy in collisions with oxygen and nitrogen, but they will also acquire energy through such collisions. Furthermore, since we are talking about half-lifes, molecules which are in an excited state have no memory of how long they have been in an excited state. Therefore so long as a certain percentage are in an excited state at any given time, a certain percentage will be emitting over any given period of time.


    Incidentally, I think we both best avoid trying to understand the thermal interaction between the atmosphere and the surface in terms of a thermal gradient. If at certain parts of the spectra, the atmosphere is transparent at the lower levels but opaque at the upper levels, it is as if lower levels don’t even exist for those parts of the spectra. And if so, the radiation won’t heat the lower level, but instead there will be the transfer of thermal energy between the surface and the layer which is opaque to the radiation for those parts of the spectra.