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Climate Feedbacks

Filed under: — group @ 3 August 2006

Guest Commentary by Brian Soden (RSMAS, Miami)

Current model estimates of the climate sensitivity, defined as the equilibrated change in global-mean surface temperature resulting from a doubling of CO2, range from 2.6 to 4.1 K, consistent with observational constraints (see previous article). This range in climate sensitivity is attributable to differences in the strength of ‘radiative feedbacks’ between models and is one of the reasons why projections of future climate change are less certain than policy makers would like.

Although radiative forcings and radiative feedbacks both influence the climate by altering the radiative fluxes at the top of the atmosphere, it is important to distinguish between the two. A radiative forcing results from changes that are external to the climate system and may be either natural or anthropogenic in origin. For example, anthropogenic emissions of CO2, changes in solar flux, and the reflection of sunlight from volcanic aerosols are all examples of radiative forcings. A radiative forcing initiates a change in climate that is distinct from the system’s internal variability. A radiative feedback, on the other hand, arises from the response of the climate to either external forcing or internal variability. These responses can either amplify (a positive feedback) or dampen (a negative feedback) the initial perturbation. The exact boundary between a feedback and a forcing depends on what is considered to be part of the ‘system’ and can sometimes be a little fuzzy. This discussion addresses just the feedbacks associated with the atmospheric physical system (see this earlier article for why that is), but other, less well understood, feedbacks (changes in land vegetation, biogeochemical processes, and atmospheric chemical feedbacks – see the NRC 2003 report), while potentially important, are not part of the generally understood definition of ‘climate sensitivity’.

In the absence of radiative forcings, the amount of sunlight absorbed by the earth roughly balances its thermal emission to space; i.e., the earth is in a quasi-steady radiative equilibrium. Doubling the concentration of CO2 decreases the emission of thermal radiation by ~4 W/m2. Because the earth is now emitting less radiation than it absorbs, there is a surplus of energy going into the system and its surface must warm. Because the thermal emission of energy increases as an object warms, the increasing temperature acts to restore radiative equilibrium. In the absence of any feedbacks, a doubling of CO2 would result in an increase in global surface temperature of ~1 K. However, as the climate warms in an attempt to restore radiative equilibrium, other changes occur. These changes can also influence the top-of-atmosphere radiative fluxes and thus act to either decrease (a negative feedback) or to increase (a positive feedback) the radiative surplus. For example, as the climate warms the amount of snow and ice cover decreases which leads to more sunlight being absorbed, thus enhancing the initial radiative surplus and requiring greater warming to restore equilibrium.

There are a number of different radiative feedbacks in the climate system, some more complex than others. Those which are most commonly represented in climate models are feedbacks from water vapor, snow/ice cover, clouds and lapse rate (the change in temperature with height).

Despite the importance of these feedbacks in determining projections of future climate change, there has never been a coordinated intercomparison of their values in GCMs. In a recent issue of the Journal of Climate, Isaac Held and I estimated the range of feedback strengths in current models using an archive of 21st century climate change experiments performed for the upcoming IPCC AR4. The results of this analysis are presented in the figure which expresses the strength of the global mean feedback for each model in terms of their impact on TOA radiative fluxes per degree global warming (units are W/m2/K).

Figure 1 from Soden and Held (2006) showing ranges for each model for each of the key atmospheric feedbacks for the IPCC AR4 models and a comparison with an earlier survey (Colman, 2003).

All models predict the concentrations of water vapor to increase as the climate warms due to the rapid increase in saturation vapor pressure with temperature. Because water vapor is the dominant greenhouse gas, this provides a strong positive feedback in the climate system. In current models, water vapor was found to provide the largest positive feedback in all models and its strength was shown to be consistent with that expected from a roughly constant relative humidity change in water vapor mixing ratio. It should be noted that models are not constrained to conserve relative humidity and significant regional changes in relative humidity are simulated by models in response to atmospheric warming. On the global scale, however, changes in relative humidity are small.

Models do exhibit a range of values for water vapor feedback. This range is not due to departures from constant relative humidity behavior, but rather from intermodel differences in the response of the atmospheric lapse rate to surface warming. All models suggest that the troposphere warms more than the surface (at equilibrium at least – responses are more varied for a short transient period – see the CCSP report). This amplified warming of the troposphere represents a key negative feedback in models because it further increases the thermal emission of energy to space. Models with more surface warming in low latitudes tend to have larger atmospheric warming (and more negative lapse rate feedback) because the surface and free troposphere are more strongly coupled in the tropics than at higher latitudes. Because the water vapor and temperature responses are tightly coupled in the troposphere, models with a larger (negative) lapse-rate feedback also have a larger (positive) water vapor feedback. These act to offset each other. As a result, it is more reasonable to consider the sum of water vapor and lapse-rate feedbacks as a single quantity when analyzing the causes of intermodel variability in climate sensitivity. As shown in the figure, the range for the sum of these two feedbacks is considerably smaller than the range of either the water vapor or lapse rate feedbacks individually.

Not surprisingly, the surface albedo feedback due to changes in snow and ice cover was also found to be positive in all models, although its magnitude is only about 25% of that from the combined “water vapor plus lapse rate” feedback.

Consistent with previous studies, clouds were found to provide the largest source of uncertainty in current models. For the most sensitive models, cloud feedback is positive and comparable in strength to the combined “water vapor plus lapse rate” feedback. For the least sensitive models, cloud feedback is close to neutral. Many specialists and non-specialists alike are sometimes surprised to see that the model-predicted values for cloud feedback ranges from neutral to strongly positive; often believing that cloud feedback is more uniformly distributed between negative and positive values. This confusion may stem, in part, from misinterpretations of the change in the easily-diagnosed “cloud radiative forcing” in model simulations of climate change. This diagnostic, based on the comparison of clear sky and cloudy sky radiation differences (Cess et al, 1996) is related to the more-difficult-to-calculate cloud feedback, but can be negatively biased by correlated changes in water vapor and temperature (Soden et al., 2004). Thus studies that use the “cloud radiative forcing” calculation have reported a more negatively skewed ‘cloud feedback’ then seen here. However, based on these estimates and on a survey of published values of feedback calculations (Colman 2003), there do not appear to be any models for which clouds provide a substantial negative feedback on the climate.

Observational studies do have the potential to help narrow the uncertainties in these individual feedbacks – for instance from studies of the response to Mt. Pinatubo and from long time series of satellite measurements – but observational constraints of cloud feedback remain elusive.

118 Responses to “Climate Feedbacks”

  1. 51
    Ike Solem says:

    In response to the comments about hydrogen producing water vapor, let’s not forget that combustion produces water vapor, taking methane for example.

    CH4 + 2 O2 -> 2 H2O + CO2 + spare energy

    The long residence time of CO2 (~100 years) compared to water vapor in the atmosphere is the central problem, as pointed out above. The choice of forcing and feedback is like the choice of system and surroundings – it is a matter of the most convenient description. Over very long time periods, one might even say that CO2 is a feedback and the Milankovitch cycles are the forcing; over ‘short’ time periods CO2 is a forcing and H2O vapor is a feedback.

    Plants run this in reverse; solar energy + CO2 + H2O -> organic carbon + O2

    So, a personal step you can take to help with the problem is to start planting trees, stop burning fossil fuels, and conserve energy as much as possible.

  2. 52
    Hans Erren says:

    According to Myhre et al. CO2 doubling has as forcing of 3.7 W/m2.
    F= 5.35 ln(2)
    Modtran only gives 3.2 W/m2

    Where does this new number 4 W/m2 come from, IMHO some positive feedbacks are already included.

  3. 53
    Steve Sadlov says:

    RE: “I’ve never seen this in my decade in S. Calif.”

    One of the things many newcomers to California are surprised by is the innate variability of both weather and climate here. Even in the reputedly “mild” mediterranean (and sliver of marine west coast up north) zones, variation can be amazing, especially on decadal and multi decadal scales. In the remaining climate zones besides the alpine, extremes are the norm. Many newcomers witness a certain set of conditions for a few years and assume that it’s “normal.” I saw this with many who arrived during the drought dominated 1980s – they thought that it was normally that sunny and dry during the winter and some actually moved out during the rainy 90s (and 00s thus far) because they could not stand the winter gloom. On the other hand, anyone who arrived here after the late 80s got a very mild temperature situation right through the turn of the century. This year’s “heat wave,” while rare, was certainly not a surprise to me. When I was a youth in the 70s, we had several very hot summers where I lived at the time (SF Peninsula) and again, a few notable ones in the mid 80s. In contrast, the short sharp 100 plus wave in late May 2000 notwithstanding, the past 10 or so summers were very much dominated by deep onshore push and essentially sucked from a warmth perspective. To be honest, for me personally, it’s nice that we’ve had some real heat this year. Too bad it was only for a mere third of the summer. I’d not be surprised if we had no more real heat this summer.

  4. 54
    sonicfrog says:

    To be honest, for me personally, it’s nice that we’ve had some real heat this year. Too bad it was only for a mere third of the summer. I’d not be surprised if we had no more real heat this summer.

    Steve, I agree. Mark, to me this is what a normal California summer feels like. But normal depends on exactly what weather pattern you first experienced when you moved to the state.

    I moved to Fresno from Dallas in ’78 and have been a resident of the state ever since, moving back and forth from Fresno to San Diego. This weather season seems much more in line with the type of weather the central valley experienced the first few years I was here in Fresno. Untill this summer, the June, July, August, months seemed not quite as hot tep wise, but much more humid, with less variation in daytime temps. This year there is a nice tempurature arch, if graphed, would look much like a standard bell curve, where previous summers would be flatter in comparison.

  5. 55
    Brian Soden says:

    Re: # 45. Sorry for the confusion Steffen. The last column in the figure represent the effective sensitivity. They range in value from 0.88 W/m2/K to 1.64 W/m2/K. If you assume a canonical value for the radiative forcing from doubling CO2 of 4W/m2, you can estimate the corresponding surface temperature change as dT=dQ/eff_sens. The low end of the range for these models is 4/1.64 = 2.4 K. The high end of the range is 4/0.88=4.5. So the estimated range for this set of models (2.4-4.5 K) is slightly larger than that referred to at the top of the article.

  6. 56
    Brian Soden says:

    Re: 19. Water vapor and surface albedo is a feedback because their changes are driven internally by the change in surface temperature. It is not a distinction betweeen gaseous and non-gaseous changes, as water vapor is itself a gas. If the amount of carbon and methane released from decaying organic matter increased or decreased in response to the temperature changes, then that would also provide a feedback onto the climate system. However, the increase in CO2 due to the burning of fossil fuels is a forcing, not a feedback, because the amount of CO2 emitted is determined by processes which are external to the climate system (energy consumption, population, etc.). The CO2 fossil fuel emissions do not arise from the change in temperature, as the water vapor/alebdo changes do. Rather they initiate the change.

  7. 57
    Leonard Evens says:

    Re #55:


    I don’t want to speak for Steffen, but perhaps he wants an explanation for how dT = dQ/eff_sens is derived and why it appears to differ from the admittedly naive estimate he came to by a different route. My guess is that there is no good way to understand these matters except to learn about the physics and how it is applied in models starting from scratch. Even then, a complex model may give results that can’t be explained more simply. After all, if there were simple physical explanations for all these things, we wouldn’t need the models. But perhaps there is some easier way to do it in this case.

  8. 58
    Brian Soden says:

    Re #37: Brian – That is a good question. The main reason why hydrogen emissions are unlikely to provide a significant radiative forcing is that the concentrations of water vapor in the atmosphere are not determined by the flux of vapor into the atmosphere, but rather by the temperature, or more precisely, by the saturation vapor pressure which depends strongly on temperature. The fluxes of water into (evaporation) and out of (precipitation) the atmosphere are in close balance and very large compared to the amount of water stored in the atmosphere. (For example, if you were able to somehow double the rate of evaporation while holding precipitation constant, the concentrations of vapor in the atmosphere would have to double in ~10 days.) In climate models, the increase in water vapor have little to do with the increase in evaporation predicted by the model. In fact, models with the same increase in evaporation can have changes in water vapor which differ by a factor of 2 or more (and vice-versa). Instead, the change in water vapor in all models is tightly coupled to the simulated change in temperature. Thus, even if the increase in H2 emissions was comparable to the increase in evaporation predicted by models (roughly 5% by 2100), this increase would be balanced by an increase in precipitation rather than an increased storage in the atmosphere. However, as you point out, there may be important localized impacts of such changes.

  9. 59
    Ron Taylor says:

    FYI, even if it doesn’t really fit here.

    Yesterday I sent an email to the NOAA Paleoclimatology people expressing surprise that their webpage on climate change had not been updated since 2000, and asked when we could expect an update. Today, I received this response from Bruce Bauer:

    “Should be sometime this fall. We have an update essentially
    complete – it is in peer review at the moment. I’ll let you know when it is ready!”

    I wonder who is doing the peer review? It will be interesting to see the product! Let us hope…

  10. 60
    Sean D says:

    RE #25, #26, #37, & #58, for a readable background on water vapor “emissions”, check this page out. Cheers.

  11. 61
    Karl Sanchez says:

    Would anyone like to comment on this ABC news video (click on the video),
    especially what is described as methane bubbling off California’s coast?

  12. 62
    Phillip Shaw says:

    Re #61: That is the scariest video I have seen in years. Does anyone know where and when it was taken?

  13. 63
    Hans Erren says:

    re 55:
    Brian introducing a term like effective sensitivity is very confusing.
    In signal processing two cases of amplification exist: transient amplification (high frequency) and equilibrium amplification (low frequency). Both terms are in fact special cases of frequency domain amplification. Can you indicate at which time scales the equilibrium takes place? Isn’t that typically 2 to 3 centuries?
    see also:

  14. 64
    Leonard Evens says:

    Re 63:

    I don’t see what signal processing has to do with the matter. I could be wrong, but I don’t believe that is a proper analogy. It seems to me you should think more in terms of what happens when you heat a pan of water by suddenly raising the temperature. CO_2 sensitivity is a measure of what the final response would be after equilibrium was achieved, if we suddently increased the CO_2 concentration by a set amount. It would generally take a while to reach equilibrium. It is not supposed to be a specific prediction but rather a basic parameter which it is important to know. But computer models can make a variety of projections based on sensitivity, on different continuous emission scenarios, and for different periods of time in the future. It is easy to find estimates for what the average global temperature will be in 2001, for example. The chart in the link you gave shows various growth curves for different emission scenarios and presumably some assumed implicit sensitivity. But the comment there you made is silly. It suggests that since up to 2030, the scenarios don’t show much difference, we can wait until then and then decide what to do. Among other things, that assumes the history up to 2030 won’t make any difference to what happens afterwards.

  15. 65
    Hank Roberts says:

    An excellent set of graphics showing predicted changes in ocean acidity over a long future time span — highly recommended! — is available in this PDF

    from the “related files” reference list here

    Press attention, e.g.:,0,6993528.story

    “As she stared down into a wide-mouthed plastic jar aboard the R/V Discoverer, Victoria Fabry peered into the future.

    “The marine snails she was studying — graceful creatures with winglike feet that help them glide through the water — had started to dissolve.

    “In 20 years of studying the snails, called pteropods, a vital ingredient in the polar food supply, the marine biologist from California State University, San Marcos had never seen such damage.

    “In a brief experiment aboard the federal research vessel plowing through rough Alaskan seas, the pteropods were sealed in jars. The carbon dioxide they exhaled made the water inside more acidic. Though slight, this change in water chemistry ravaged the snails’ translucent shells….”

  16. 66
    Karl Sanchez says:

    Hi Phillip,

    This is from the text that accompanied the video, ” about 20 meters down off the coast of Santa Barbara, Calif.: bubbles, millions of bubbles of methane â?? 20 times more powerful as a greenhouse gas than carbon dioxide.

    The methane is bubbling up naturally from some of the enormous natural undersea reservoirs of the gas mostly locked into the frozen mud under the sea floor.

    Scientists have just released video showing how, for the first time, they have been able to measure these natural up-wellings to tell whether, if large amounts of this methane ever thawed out from its deep sea beds, it would reach the atmosphere, rather than being absorbed in the water, and thus make the earth even hotter.

    The findings of oceanographer Ira Leifer et al, published in a strictly peer-reviewed scientific journal, are that it would do just that.

    In other words, all that undersea methane is a potential ‘positive feedback’ of catastrophic proportions.”

    I wonder if a method might be devised that vacuums the released methane? I know there’re schemes for mining it, but why mine when it’s being freely released?

    And one must wonder how many other methane beds are madly bubbling away from camera sight?

  17. 67
    Karl Sanchez says:

    Here’s a link to an article that discusses Leifer’s research and findings and provides further context for the video.–gef071906.php

  18. 68
    Phillip Shaw says:


    Thank you for the info and the link to the article. If I understood the article, the video is of a natural gas blowout that occurred in 2002, not a methane hydrate blowout. That’s a lot less scary.

    Southern California is known for petroleum seeps, both on land and underwater. A famous one is the La Brea tarpits in Los Angeles. A pocket of methane bubbling up in shallow near-shore water is not particularly alarming. So I’ll stop hyperventilating. :-)

    Thanks again.

  19. 69
    Hank Roberts says:

    Natural gas is “50 to 90 percent methane.”

    The research — this is a major issue being looked at in many areas — addresses how much gas reaches the atmosphere — rather than redissolving in the overlying seawater.

    Brief answer: slow steady trickles of bubbles redissolve; large columns make it into the atmosphere.

    The area of sea floor involved is huge, and massive releases in the past involve collapses of the continental slope seafloor into the abyss.

  20. 70
    Hank Roberts says:

    References in PDF format:

  21. 71
    Steve Sadlov says:

    RE: #61 – Beyond the viral popups that killed my Mozilla, I have some real problems with the false claim of methane coming up beneath frozen mud off of SB. Firstly, what bubbles up there is actually mostly hydrogen sulfide, not methane. And it is from the same trends as the oil deposits, not some shallow deposits below so called frozen mud. And because the entire area of the So Cal coast is continental crust, and non abyssal, while certainly there are deep water temps down in the upper 30s, there ain’t no frozen mud. [edited]

  22. 72
    Hank Roberts says:

    re #71, Steve Sadlov

    Got facts? Who provides your information? I’m seeing this claim the gas is “not methane” suddenly a lot, it must be coming from some source people are reading criticizing this story. Please, where did you read it? And why do you believe them?

    Got methane? Here’s what I found, among the cites I posted above, just before your #71.

    “Compositional changes in natural gas bubble plumes: observations from the Coal Oil Point marine hydrocarbon seepfield….

    Received: 22 January 2002/ Accepted: 22 July 2003/ Published online: 3 October 2003 Springer-Verlag 2003

    Detailed measurements of bubble composition, dissolved gas concentrations, and plume dynamics were conducted during a 9-month period at a very intense, shallow (22-m water depth) marine hydrocarbon seep in the Santa Barbara Channel, California. Methane, carbon dioxide, and heavier hydrocarbons were lost from rising seep bubbles, while nitrogen and oxygen were gained. Within the rising seawater bubble plume, dissolved methane concentrations were more than 4 orders of magnitude greater than atmospheric equilibrium concentrations. Strong upwelling �ows were observed and bubble-rise times were ~40s, demonstrating the rapid exchange of gases within the bubble plume.

  23. 73
    Ike Solem says:

    Regarding the posts on methane/hydrocarbon seeps and venting, I think the area of concern here is the northern permaforst regions, which are going to be warming a lot faster then the deeper ocean is – but shallow areas are a concern. I’m guessing that by the time the ocean warms that much, the thermal expansion will already have drowned most coastal cities.

    For a news story on the permaforst issue, see:
    Guardian: “Warming hits ‘tipping point’”.

    For a more detailed report, see:
    “The largest source of natural gases, mostly composed of CH4 , is stored in gas-hydrates beneath permafrost and the onshore permafrost reservoir is roughly estimated to be as much as 32,000 Gt. (1Gt = 109 tons). This is 106, or one million, times as much as the CH4 released in the atmosphere of all northern ecosystems. Dr. Shakhova feels that a very small disturbance of gas hydrates could cause catastrophic consequences within a few decades. Shallow bottom sediment and underlying permafrost have warmed approximately 15°C since the time they originated. The implications of this trend are that shallow off-shore gas hydrate deposits could become vulnerable (Fig.2). She also notes that methane plumes found in the East-Siberian Sea (ESS) during the 1 st and 2nd Russian-U.S. joint cruises during September of 2003 and 2004 may indicate decaying gas hydrates in thawing undersea permafrost.”

    This is a big worry; I’m very interested to see what the next IPCC report makes of this.

  24. 74
    Karl Sanchez says:

    Seeps happen to be rather inconvenient right now as any GHG added no matter the source adds to the problem. It’s said that seepage from deepwater is absorbed by the ocean, but wouldn’t this also help fill the capacity of the ocean as GHG sink sooner rather than later? Surely, at some point the ocean can only hold so much methane before it starts offgassing rather than absorbing?

  25. 75
    Brian Gordon says:

    Re 58: Thanks Brian!

    Re: CH4: It seems there are so many things going wrong that a holistic approach – sustainability – may be the only answer.

    In other news today:
    “The proposals involve pumping [CO2] gas miles underground then injecting it under the sea floor.

    There is enough space for almost unlimited carbon emissions, a US team reports in the Proceedings of the National Academy of Sciences.”
    [Which I take to mean that the 'problem' of CO2 emissions has thus been 'solved' by technology.]
    “In the current issue of the journal Climate Change, Paul Crutzen of Germany’s Max Planck Institute for Chemistry suggests injecting particles of sulfur into the stratosphereâ��the upper layer of the atmosphereâ��to cool the planet and buy time for humans to reduce greenhouse gas emissions.”

  26. 76
    Hans Erren says:

    re 64:
    Signal processing has everything to do with climate sensitivity. The system earth is a feedback amplifier which responses like a low pass filter to forcings, this meeans the lower the frequency of the signal, the higher the response, that’s why the earth reacts to low frequency signals like Milankovitch orbital changes. This is also the reason why you can’t simply plug in an ice age sensitivity into models that only look at a centuries duration.

  27. 77
    Hank Roberts says:

    A polite nudge again to those who’ve posted above your belief that the seeps discussed are “not methane” –

    Who provides your information? I’m seeing this claim the gas is “not methane” suddenly a lot, it must be coming from some source people are reading criticizing this story. Please, where did you read it? And why do you believe them?

  28. 78
    George Landis says:

    I do hope many on this site saw this article yesterday in USA Today, you might learn something if you open your minds to new ideas and sage thoughts.

  29. 79
    Leonard Evens says:

    Re 76:
    “Signal processing has everything to do with climate sensitivity. The system earth is a feedback amplifier which responses like a low pass filter to forcings …”

    As someone who has had extensive training in physics and mathematics, but who is still very much an amateur in climate science, this statement seems to me to be an example of throwing words around with little of substance behind them. Would someone, beside the originator of the statement, be willing to comment further? It is certainly possible to treat any physical system using a particular mathematical approach, and sometimes this is useful. But in the current situation, it seems to me that such an approach is fruitless. For one thing, to apply analyses of this kind, it would have to be true that a decomposition of the input into periodic components translates simply into a correponding decomposition of the output. If we could figure out what was happening to climate that simply, we wouldn’t need complex models.

  30. 80
    Hank Roberts says:

    >78, George Landis

    Thanks to pointing out the source for this. I checked THEIR statement. It’s, to put it as politely as possible, utter bullshit.

    If you look this up (“Google is your friend”) you’ll discover the distortion in the USA Today article turns the sense upside down.

    Schneider warned that _geoengineering_ of the sort just recently discussed could overshoot, risking conditions like the ‘Little Ice Age’.

    Got that? Not “Ice Age” but “Little Ice Age” — a historical period. Not “coming Ice Age” but risk of overshooting geoengineering of climate.

    It was a smart, reasonable caution, and it’s being totally misrepresented.

    It took me all of 30 seconds to find this out. USA Today failed badly.

    Here’s a citation, a quote from it and the relevant footnote to undetstand what his Genesis Strategy book had suggested:
    Reproduced, with permission, from: Schneider, S. H. 1989. The greenhouse effect: Science and policy. Science 243: 771-81.

    “Policy responses. The last stage in diagnosing the greenhouse effect concerns the question of appropriate policy responses. Three classes of actions could be considered. First, engineering countermeasures: purposeful interventions in the environment to minimize the potential effects [for example, deliberately spreading dust in the stratosphere to reflect some extra sunlight to cool the climate as a countermeasure to the inadvertent CO2 warming (60)]. These countermeasures suffer from the immediate and obvious flaw that if there is admitted uncertainty associated with predicting the unintentional consequences of human activities, then likewise substantial uncertainty surrounds any deliberate climatic modification. Thus, it is quite possible that the unintentional change might be overestimated by computer models and the intentional change underestimated, in which case human intervention would be a “cure worse than the disease” (61).
    61. S.H. Schneider and L.E. Mesirow, The Genesis Strategy: Climate and Global Survival (Plenum, New York, 1976), chap. 7, p. 215.

  31. 81
    Dan says:

    re: 80. And what is sad is that the original post referenced a *newspaper*, USA Today, as if it a newspaper is the proper source of scientific information!

  32. 82
    Chuck Booth says:

    Re #78 George,
    I’m not clear how Craig Bohren’s response (in both his answer to the question and in his sidebar observations) is expected to open anyone’s eyes to “new ideas and sage thoughts” – nothing he says is new, and much (if not all) of it is already discussed and debated in great detail at And, in my humble opinion, his observation that “it is fair to say that another Ice Age would be equally or more catastrophic for Earth than global warming” has no relevance whatsoever to a discussion about climate over the next few centuries.
    More to the point, he does seem to acknowledge that global warming is real and that fossil fuel combustion could be a contributing factor, though perhaps less a factor than some of the contributors and posters at this site.
    Actually, I am a bit surpised that Bohren is as receptive to the reality of global warming as he seems to be. After all, he was quite skeptical about it, and the greenhouse effect, 20 years ago: In his 1987 book, Clouds in a Glass of Beer (Wiley), he argued in Chapter 10 that no one really understands how a greenhouse works – it may work by trapping infrared radiation (solar infrared penetrates the glass, or plastic, warms the objects within, and the emitted terrestrial infrared can’t escape), or by suppressing convective heat transfer (that is, providing a shelter from the wind; the thickness of the glass is also a likely factor here). He then concludes that both views are supported by the experimental evidence, hence, they are both correct (or both wrong). I have no problem with that, but he uses this alleged confusion about the greenhouse effect to cast doubt about global warming. As in the USA Today article you cited, he conceded that atmospheric CO2 is rising, but dismisses the concerns because the effects of rising CO2 can’t be predicted as accurately as he would like (he didn’t trust the computer models back then, either).
    Bottom line: He is a knowledgeable scientist who makes some valid points, but chooses to focus on the uncertainty about projections. Nevertheless, in the USA-Today article sidebar, he offers the same advice that is offered by folks posting on this site:
    “A prudent society would reduce its dependence on fossil fuels, especially oil, as quickly as possible for many reasons, not just the possibility of global warming. A prudent society would also develop drought-resistant crops and make other long-term plans for inevitable climate change of any kind.” Of course, his advocacy for nuclear power will not sit well with many people (personally, I nuclear power doesn’t frighten me, but I don’t see it as a panacea – there are valid arguments that it won’t do much to cut our reliance on fossil fuels).
    Bottom line: The article was interesting, but it says nothing new that I can see.

    BTW: Bohren’s book, Clouds in a Glass of Beer, is a very good read (at least from my point of view as a biologist)- lots of clever experiments that can be done at home to illustrate basic principles of atmospheric physics, and explanations for natural phenomena we see outdoors.

  33. 83
    Chuck Booth says:

    Re # 82 Clarification:
    In my previous post I wrote: “he does seem to acknowledge that global warming is real and that fossil fuel combustion could be a contributing factor, though perhaps less a factor than some of the contributors and posters at this site.” I meant not as much of a factor as contributors and posters to this site believe it to be. I was not implying that the CO2 (or other greenhouse gases) expelled by the people posting here is contributing to AGW.

  34. 84
    Ron Taylor says:

    Re 78, 82

    I agree that Bohren has said nothing that is new or helpful. Frankly, much of the text seems to be the pointless meanderings of an aging mind. He reminds me of older men I know who think that everything taking place in the world can be interpreted in terms of their own life experiences. (FYI, I am near 70.) Perhaps that helps explain his utter contempt for computer modeling and modelers, which I find a bit astonishing.

  35. 85
    Taylor says:

    Re #72 and others: The Coal Oil Point seep has been going on for years. In the early 1980s I was part of a team that measured the volume of gas; it amounted to about 6 tons per day. It was mostly methane, but there were significant amounts of higher order alkanes (ethane, propane,etc.). Quite a bit of H2S as well (it smelled REALLY bad!). Our study was sufficient to convince ARCO to build an underwater “umbrella” that captured most of the gas and sent it ashore via pipleline to a processing plant. ARCO received emission credits from the local air pollution control district for doing so.
    The bonus was that the beaches of Santa Barbara (my home town) became much less covered with tar!

  36. 86
    Steve Sadlov says:

    RE: #85 – I remember well being a fellow Santa Barbarian of that era! :)

  37. 87
    Steve Reynolds says:


    Since this was published in 1989, how does it refute Bohren’s comment about statements made 30 years ago?

    The reference to the 1976 book is too brief to show much.

  38. 88
    julian flood says:

    With an unpolluted ocean, warming should lead to increased upwelling and a more efficient biological pump — negative. A more efficient biological pump should lead to increased production of DMS and an increase in low-level cloud — negative.

    With an unpolluted ocean surface, warmer climate should lead to increased storm activity, more hygroscopic nuclei in the lower atmosphere and increased albedo — negative. Increased wave activity should lead to increased mechanical uptake of CO2 by the oceans — negative.

    I’d love to see the climate numbers crunched with allowance made for the fact that .25% of oil production is spilt on the sea, .1% is turned into surfactant and both these pollutants mitigate the above effects. The petrochemical industry took off at just the right time to produce the hockey stick. Persistent surfactant production ties in nicely with the ’40s uptick.

    It started as a spoof new theory of global warming (see but the more I look at it the more worried I become. Maybe someone has done the figures?

  39. 89
    George Landis says:

    RE: 87
    It doesn’t, but why question an obvious ad hominem attack on the professor.

  40. 90
    Hank Roberts says:

    >87, 80 — Steve, I gave that as an example after a brief search you can do in Google. You’ll notice the accusations of an ‘ice age’ are from the septical PR sites, and the accurate descriptions of a reference to risks from geoengineering recreating the ‘Little Ice Age’ are from the science journals. Look into this kind of accusation when you see climate scientists pilloried in the popular press, that’s my suggestion and point.
    You’ll want to make up your own mind. I’m suggesting getting citations and reading them rather than relying on USA Today for your scientific basis.

    >88 — Cute idea, maybe credible, but I notice they casually dismiss ocen acidification as not likely with no basis at all; look at the published research for the actual figures and levels at which aragonite shells dissolve, and you’ll see the physical chemistry basis for the prediction of major effects by 2100.

  41. 91
    Hank Roberts says:

    > 88 — hey, “natural” experiment?

    Alaska Oil pipeline will shut down at least til December! Which, I think, means oil tanker traffic and normal spills from associated tanker traffic will be reduced or ended.

    I don’t have any idea how the volume spilled from normal shipping would compare to the amount still entering the ocean fromthe Exxon Valdez spill after 17 years.

    The other natural experiment would be to find research done in areas that subsequently have large oil spills — of which there are plenty.

    Is an interesting opportunity, if anyone knows how to look into it.

  42. 92
    Jeffrey Davis says:

    A theory like that is simply either a dog-in-the-manger or a false elaboration since all theories must accomodate the heat that the established physics of the current model produces.

  43. 93
    Hank Roberts says:

    Agreed, even if it’s happening, it doesn’t change the greenhouse effect from fossil fuel use.
    And the assumption made — that an unpolluted ocean would generate more negative feedbacks because it would produce more couds — assumes more than we know about cloud feedbacks.


  44. 94
    Chuck Booth says:

    Re #88. “With an unpolluted ocean, warming should lead to increased upwelling”

    Really? How so? Can you please explain this prediction?

  45. 95
    Hans Erren says:

    IPCC TAR chapter 6.2.1
    “lambda is a nearly invariant parameter (typically, about 0.5 K/(Wm-2); Ramanathan et al., 1985) for a variety of radiative forcings”

    This statement is challenged, lambda is different for solar and CO2, and it is also not an invariant for forcing frequency. lambda is much smaller for fast varying forcings like volcanic sulphate pulsated cooling.

    [Response: Possibly we are not reading the same sentence. 'lambda' is 'nearly' invariant - true, and of course lambda defined is for equilibirum changes and works well for long term volcanic forcing regardless of it's fast varying pulsing. If you are going to keep insisting, at least find some actual evidence that supports your case. - gavin]

  46. 96
    Martin Lewitt says:

    Dr. Soden, wouldn’t it be more correct to characterize cloud feedback as a sink of model uncertainty rather than as a source? As you noted, cloud feedback is poorly constrained by observations. In practice, modelers tweak cloud parameters to balance global energy budgets or to match albedo observations, and consequently, perhaps unintentionally, use cloud parameters to cover model errors from numerous sources, rather than to achieve cloud feedback realism as their first order priority for these parameters. In a nonlinear system, it would be fortuitious, if this general method of correcting model errors were equivilent to more specific corrections.

  47. 97
    Hank Roberts says:

    Satellite results:

    “… we provide a measurement-based assessment of the global direct climate forcing (DCF) of anthropogenic aerosols at the top of atmosphere (TOA) only for cloud free oceans. The mean TOA DCF of anthropogenic aerosols over cloud-free oceans [60Nâ��60S] is â��1.4 ± 0.9 Wmâ��2, which is in excellent agreement (mean value of â��1.4 Wmâ��2) with a recent observational study by Kaufman et al. [2005].”

  48. 98
    Mark says:

    Just out of curiousity, has ANYONE done any real world testing in a lab environment to prove or disprove ANY of these theories?

  49. 99
    Hank Roberts says:


    “Real-world testing” is not done “in a lab environment” — it’s hard to get good controls for planet sized experiments.

    Did you read the article linked in 97? Or the bit I quoted from it?
    If so, what is it you don’t understand about the reports of satellite data confirming modeling?

  50. 100

    Re #98 Climate science is not like physics. You cannnot run an experiment to find out what would happen to the Earth with double CO2, then decide what to do with the real Earth. If you use a cliamte models to predict the climate, you cannot check that the climate model’s predictions are right until the fifty years has expired. Even if the model fits today’s climate, you can never be sure it will get future climate correct. That is a fact of life, not some clever argument from a sceptic.

    In fact the models are wrong, but because they give the “correct” results for today (provided you frig the MSU and radiosonde results) everyone thinks they are right!

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