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The certainty of uncertainty

Filed under: — group @ 26 October 2007

A paper on climate sensitivity today in Science will no doubt see a great deal of press in the next few weeks. In “Why is climate sensitivity so unpredictable?”, Gerard Roe and Marcia Baker explore the origin of the range of climate sensitivities typically cited in the literature. In particular they seek to explain the characteristic shape of the distribution of estimated climate sensitivities. This distribution includes a long tail towards values much higher than the standard 2-4.5 degrees C change in temperature (for a doubling of CO2) commonly referred to.

In essence, what Roe and Baker show is that this characteristic shape arises from the non-linear relationship between the strength of climate feedbacks (f) and the resulting temperature response (deltaT), which is proportional to 1/(1-f). They show that this places a strong constraint on our ability to determine a specific “true” value of climate sensitivity, S. These results could well be taken to suggest that climate sensitivity is so uncertain as to be effectively unknowable. This would be quite wrong.

The IPCC Summary For Policymakers shows the graph below for a business-as-usual carbon emissions scenario, comparing temperatures in the 1980s with temperatures in the 2020s (orange) and 2090s (red). The latter period is roughly when CO2 will have doubled under this scenario. The resulting global temperature changes cluster between 2 and 5 degrees C, but with a non-zero probability of a small negative temperature change and long tail suggesting somewhat higher probabilities of a very high temperature change (up to 8 degrees is shown).

We have very strong evidence for the middle range of climate sensitivities cited by the IPCC. But what Roe and Baker emphasize is that ruling out very high sensitivites is very difficult because even the relatively small feedbacks, if they are highly uncertain, can have a very large impact on our ability to determine S.

Paleoclimate data do provide a means to constrain the tail on the distribution and perhaps to show the likelihood of large values of S is lower than Roe and Baker’s calculations suggest. In particular, Annan and Hargreaves (2006) used a Bayesian statistical approach that combines information from both 20th century observations and from last glacial maximum data to produce an estimate of climate sensitivity that is much better constrained than by either set of observations alone (see our post on this, here). Their result is a mean value of deltaT close to 3ºC, and a high probability that the sensitivity is less than 4.5ºC, for a doubling of CO2 above pre-industrial levels. Thus, we emphasize that Roe and Baker’s result do not really tell us that, for example, 11°C of global warming in the next century entury is any likelier than we have suggested previously.

On the other hand, there is a counterpoint to such a comforting result. Roe and Baker note that the extreme warmth of the Eocene — something that has stymied climate modelers — could in principle be explained by not-very-dramatic changes in the strengths of the feedbacks, again because small changes in f can produce dramatic change in S. The boundary conditions for Eocene climate remain too poorly known to include in a formal calculation of climate sensitivity, but at the very least the extreme climate of this time suggests that we cannot readily cut the tail off the probability distribution of S.

It would be wrong to think that climate scientists have been ignorant of the non-linear nature of feedbacks on climate sensitivity. Several papers dating back a couple of decades show essentially the same result (for example, Hansen et al., 1984; Schlesinger, 1988; see below for full citations). But Roe and Baker’s paper is probably the most succinct and accessible treatment of the subject to date, and is a timely reminder of some very basic points that are not always appreciated. For example, it is often assumed that the tail on the distribution of climate sensitivity is due to the large uncertainty in some feedbacks, particularly clouds. Roe and Baker make it very clear that this is not the case. (The tail in S results from the probability distribution of the feedback strengths, and unless those uncertainties are distributed very, very differently than the Gaussian distribution assumed by Roe and Baker, the tail will remain). Furthermore, they point out that “uncertainty” in the feedbacks need not mean “lack of knowledge” but may also reflect the complexity of the feedback processes themselves. That is to say, because the strength of the feedbacks are themselves variable, the true climate sensitivity (not just our ability to know what it is) is inherently uncertain.

What will get the most discussion in the popular press, of course, are the policy implications of Roe and Baker’s paper. Myles Allen and David Frame take a stab at this in their Perspective.* Their chief point is that it is probably a bad idea to assign a specific threshold value for CO2 concentrations in the atmosphere, above which “dangerous interference in the climate system” may result. For example, 450 ppm is an oft-cited threshold since this keeps deltaT below 2°C using standard climate sensitivities. But the skewed nature of the distribution of possible sensitivities means that it is much more likely that 450 ppm will give us more than 4.5°C of global warming rather than less than 2°.

Allen and Frame suggest that the way to address this is though an adaptive climate change policy, in which there are movable CO2 concentration targets that can be revised downwards if future observations suggest that the climate sensitivity is indeed greater than the middle IPCC range. We agree that adaptive policies are needed. There is no point in continuing to pursue a 450 ppm stabilization goal in the eventuality that temperatures have already exceeded the expected 2 deg C. More reductions would be called for. Similarly, if temperature rises more slowly than expected, that would buy time. However, in our view, Allen and Frame’s discussion turns the precautionary principle on its head by implying that downward revision can always be done later, after more data are in. But a good adaptive strategy depends on nimble action and forward thinking — both of which are typically in short supply. If reactions to a worse-than-expected climate change are delayed, they make an overshoot of any temperature target very likely, and corrective action very expensive. Thus conservative strategies would seem in order, which probably implies initial targets of much lower than 450 ppm, and still subject to further revision.

The bottom line is that climate sensitivity is uncertain, but we can pretty much rule out low values that would imply there is nothing to worry about. The possibility of high values will be much harder to rule out. This is something policy makers should recognize and confront.


Hansen, J.E., et al., in Climate Processes and Climate Sensitivity, J. E. Hansen, T. Takahashi, Eds. (Geophysical Monograph 29, American Geophysical Union, Washington, DC, 1984), pp. 130–163.
Schlesinger, M.E., 1988: Quantitative analysis of feedbacks in climate model simulations of CO2-induced warming. In Physically-Based Modelling and Simulation of Climate and Climatic Change, M. E. Schlesinger, Ed., NATO Advanced Study Institute Series, Kluwer, Dordrecht, 653-736.
*See also the news article in Nature. And our congratulations to Myles Allen and his colleagues who won the Euro Prix award for their climateprediction.net work.


251 Responses to “The certainty of uncertainty”

  1. 51

    Hi,
    I am an alternative planners for electricity and energy utilization, Indonesia. I may say the only one. As a national planner, I am looking for formal and strongest identification problem, such as from consumers to cooperatives.

    Please look a great case of the captive market of combined heat and power (CHP) as vizualized by American Institute of Physics:
    http://www.aip.org/pt/vol-53/iss-11/captions/p29box2.html

    My remark under uncertainty and certainty remains, placing Cooperative CHP between public electricity and private industry. The benefits are
    IEC can be implemented for public electricity
    ISO can be implemented for private industry
    ITU can be implemented for cooperative CHP.

    The reverse of Cooperative CHP is Multi Purpose Dam:

    http://www.ia-itb.com/node/445

    We faced parallel danger or the certainty of uncertainty.

    Keywords: reliability engineering, interdependency, intellectual property

  2. 52
    Dave Rado says:

    Re. #46, in the interior of polar continents and very large islands (Antarctica, Greenland), increased precipitation as snow resulting from the increase in warmer air’s capacity to hold moisture, results in an increase in ice mass balance. But at the periphery of Antarctica and Greenland, the ice is melting rapidly.

    In addition, in the case of Antarctica, the ocean currents there buffer it to a large extent, as a result of which increased heat from global warming is not carried there from the tropics at anything like the rate that it is carried to the Arctic. And ozone depletion has also tended to cool the Antarctic. For more on this see here).

    The trend for both the observed and modelled overall ice mass balance is very rapidly negative in the case of Greenland and slightly negative in the case of Antarctica – although the Antarctic peninsula is one of the most rapidly warming and melting regions on earth, and although there are serious worries that some very large ice shelves in Antarctica are prone to extremely rapid collapse followed by melting, as has already happened in the case of Larsen B, an ice shelf approximately the size of Luxembourg which collapsed in only 3 days – and that this phenomenon could possibly have a big impact in rates of sea level rise in the coming century.

    Outside of Greenland and Antarctica, glaciers are indeed melting almost everywhere, at an extremely rapid rate. The overall global glacier mass balance trend is shown on the National Snow and Ice Data Center (NDIS) graph here. The NDIS website is well worth exploring.

    With respect to of glacier loss outside of the Greenland and Antarctica, the biggest worry is not so much the effect on sea level (although they too will affect sea level), but more seriously, the severe permanent droughts that will result. Many hundreds of millions of people (and huge ecosystems) rely for their water on the annual glacier summer melts that in many cases may cease during the next 50-100 years, as mountain glaciers start to disappear.

  3. 53
    GlenFergus says:

    #45:

    Yes. Cecilia Bitz’s group’s sea ice projections actually don’t look too bad. Here’s her Fig 2 updated with the Sept’07 sea ice extent. The general shape of the 2007 decline is well replicated in Run 5; it just has it a touch later (about 2013). Modelling conservatism, perhaps?

    For now, the large Beaufort Sea – East Siberian Sea SST anomaly continues to decay. Refreeze cannot be far off. Await next summer with interest…

  4. 54
    Kevin says:

    Re: 46

    How does the information in that article contradict the “ice melting everywhere” theory? Of course no such theory exists, or if it does perhaps you should provide a link. The current models acknowledge that some glaciers may grow (very few are).

    From your link:
    “In some instances, bright red spots or streaks along the edge of the continent show where icebergs calved or ice shelves disintegrated, meaning the satellite began seeing warmer ocean water where there had previously been ice.”

    I guess the ice is melting in the antartic, at the edges — as expected.

  5. 55
    Lynn Vincentnathan says:

    RE #18 & “as changes get larger, the sensitivity may grow or shrink”

    I’m not sure if I’m getting this right, but from what I understand from earlier discussions is that the sensitivity re how much warming happens given a certain increase in CO2 (if we could know exactly what it is) stays the same or decreases somewhat with increased CO2e input. I think there is a log relationship, but for our considerations of doubling CO2 it looks fairly linear. I think it’s more a matter of the physics of the situation, and the sky is just too big a lab and the experiment still ongoing to get exact results and there are these pesky “internal” feedbacks — such as water vapor and clouds.* [*I’m not sure, but I think this is what “f” refers to, and not the “external” feedbacks I mention below.]

    The point I was trying (but perhaps failing) to make in #11 was that there are greater uncertainties than that of the CO2/warming sensitivity regarding how nature would respond to the warming (in many many ways) — nature’s various “sensitivities” both to the warming and to concomitant factors (methane from melting permafrost & hydrates; CO2 reaching optimal levels for plants, then becoming more a pollutant, etc), which makes the amount of CO2 released into (or not absorbed from) the atmosphere uncertain. Maybe not right now, but in the future.

    So while the sensitivity of CO2/warming may be an important (though somewhat uncertain) matter, so too is how sensitive nature is in emitting GHGs in response to the warming (& to the concomitant GW effects), and this it seems is a lot more uncertain and has a lot more potential for danger…like some sleeping monster we keep poking.

    So even if the CO2/warming sensitivity is low, if nature’s sensitivity to the warming is high & a whole lot of GHGs get released, then the warming might go really high, perhaps higher than if the C02/warming sensitivity were higher, but nature’s sensitivity (net GHG emissions in response to the warming) were lower.

    Someone please let me know if I’m getting this wrong.

  6. 56
    Robin Johnson says:

    Re #20:

    • plants in a hotter climate are darker

    Karen-

    I don’t mean to pick. But where did you get that from? As a general rule, leaves are actually darker when there is less sunlight (shade, higher latitudes and lower altitude). Many plants will adjust their color (over time) to the amount of sunlight by changing leaf color (assuming they are otherwise healthy).

    As far as CO2 fertilization, plants can only use so much CO2 (the limits of minerals, water, nitrates and sunlight tend to be more important for most plant ecosystems).

    But an interesting side-effect is that the leaves need to respire LESS – which means the plant loses less water which means that more CO2 makes the plants more drought tolerant. This also increases soil moisture and reduces plant take up of rainfall. The latter along with increasing glacier melt has led to river flow increases – particularly in China and India which has led to more food production – and unfortunately a large increase in population – and well… a large increase in human suffering in the coming decades.

  7. 57

    Please, please show me just one quantitative paper where a doubling of atmospheric CO2 produces a temperature change of X or Y degrees, even if it’s negative. All I have been able to find is left-overs in GCMs which have been blithely ascribed to CO2, plus a bit of spectroscopy, lab style, that I was taught in the 60s. Several of us have been looking, but nowhere can we find a defining paper that is quantitative, that shows where in the atmosphere the temperature change occurs and what its magnitude, sign and uncertainty are. No need to reference anything from IPCC, it has been searched for a nill result.

    Since this is a foundation stone question for anthropogenic global warming, we think that someone ought to have made an attempt to confirm the modelled hypotheses.

    No silly answers please. This is a serious question.

    [Response: It is one we have dealt with many times before: e.g. here and here. – gavin]

  8. 58
    Charles Muller says:

    #34 Timothy, #27 Pascal, #19 Karen

    Thank you for your answers. In fact, “empirical” evaluation of each positive or negative feedback contributing to climate sensitivity was not my point here. I’ve now read carefully the Roe and Baker paper, so I better undestand their method and purpose (at least, I hope). They demonstrate or explain more precisely the asmytric relationship between f and S in present climate models (so, they use mean or better estimates of these models without any opinion about the quality of these estimates). There’s no real progress in our evaluation of climate sensitivity, rather the demonstration that real progress will be very difficut to reach (worse even, the range should enlarge as we include more and more parameters for evaluation of f, so more and more uncertainty because each new parameter will have its own distribution of probability).

    Concerning the CS from an empirical /physical perspective, there would be much more to say. For example, Spencer et al 2007 analysis of recent and precise climatologies suggests that the iris effect is not dead, after all, and the order of magnitude of the negative feedback (-6W/m2 TOA for warm tropical events) is interesting. Fortunately, the scientific research is still open and all hypothesis need to be carefully adressed.

  9. 59
    petefontana says:

    Dave Rado #52, thanks. That’s a very useful and detailed response. I do have a couple of observations. Some prominent individuals have suggested that the disintegration of the West Antarctic Ice Sheet is part of an overall climate “tipping point.” I have heard that is supposed to be reached by December 6, 2015.
    The whole positive/negative AO AAO thing seems highly variable. I’ve looked at those charts, too. And the increasing cold at the poles seems strange. Is a catastrophic double polar meltdown really a certainty? Let’s hope not.

    Towards the lower latitudes, I certainly hope hundreds of millions of people are not overly dependant on glacier fed water supplies. If they are, was this ever a good idea?

  10. 60
    Nigel Williams says:

    Nick 44. That was my thought too. With the Antarctic sea ice maximum observed this year I wondered if it was due to the sub-surface melt lakes discharging fresh super-chilled water out under the ice sheets. This then rises to the sea surface enhancing the extent of freezing pack ice. The extent of pack ice could perhaps be correlated to the ice mass loss. Maybe?

  11. 61
    SCM says:

    The article above says:

    For example, 450 ppm is an oft-cited threshold since this keeps deltaT below 2°C using standard climate sensitivities. But the skewed nature of the distribution of possible sensitivities means that it is much more likely that 450 ppm will give us more than 4.5°C of global warming rather than less than 2°.

    If 2 degrees is the most likely value (for 450ppm) then the above statement doesn’t seem to make sense. Surely there would be approx 50% probability of less than 2 degrees and a rather lower probability for more than 4.5.

    Was the last bit supposed to read “less than zero degrees”?

  12. 62
    Karen Street says:

    Re #56

    John Harte discussed a shift to darker plants at the China US Climate Change forum in Berkeley. Here is an explanation for the public. He said — there or elsewhere — that the ice age ended so quickly in part because spruce trees chased the ice away — ice disappeared to be replaced by spruce trees which warmed the area which caused more ice to disappear.

    Harte warmed an area in the Rockies to see what happens, and found sagebrush replacing leafy perennials.

    The heated meadow began to look different-more desertlike than pastoral-but the changes weren’t just aesthetic. Sagebrush is much less reflective than the flowers; where the light-colored flowers once reflected much of the sun’s energy back into space, sagebrush, with its dark bark, absorbed it. So as the sagebrush spread, the meadow began to grow even warmer.

    …Sagebrush, by comparison [with the flowers], is less active at photosynthesis and it produces far less plant material each year. As the sagebrush spread, Harte began to observe a disturbing trend: The carbon that was bound up in the soil continued to be released through the work of microbes, but now it was no longer being replaced.

    Plants of one species may change color with the amount of sunlight, but there is also a shift in species with temperature.

    Plants may leave more water in the soil with increased CO2 in areas where temperature does not rise. The expected increase in temperature will more than compensate for the extra CO2 and dry out the soil.

    Also, as Harte showed, species selected for a warmer climate sequester less carbon, so the amount of carbon stored in biota will decrease, at least in Alpine regions.

  13. 63
    Lynn Vincentnathan says:

    #59 & “I certainly hope hundreds of millions of people are not overly dependant on glacier fed water supplies”

    That’s about right. A large chunk of humanity is dependent on glacier melt (also snowpack melt — e.g., I think in the U.S. west). This includes among other peoples 40% of India’s and China’s populations, which comes to 500 million people, but doesn’t include the many millions of glacier-dependent people elsewere.

    But rather than suggest is was a bad idea to become dependent on the glacier and snowpack melt cycles, I think it was a bad idea to become dependent on fossil fuels, and a bad idea to still be so addicted to them right now, when I’m sure we could reduced our consumption worldwide by at least 70% without much harm to the economy. Tho it would take years and decades to make the transition. And we really should have started that back in the 1970s during the 1st energy crunch, then ratcheted way up by the late 1980s, when the world became aware of the GW dangers. Then we’d nearly be there by now (and the scientists would be even more uncertain about sensitivity & other aspects of GW :)). The tech is there; for instance, passive solar has been known about and practiced for over 2000 years — but not by profligate us!

    RE “double polar meltdown” I’ve never heard that (and I suppose it wouldn’t happen for many many centuries, if at all it does happen). Perhaps you’re equating the West Antarctic Ice Sheet (which IS melting and disintegrating) with the whole of Antarctica — a much larger area, much of which is not yet so affected by GW.

  14. 64
    Lynn Vincentnathan says:

    So what exactly do Roe & Baker include in “f” feedbacks? (I don’t have access to the article.) Is it what I think — water vapor and clouds. Or does it include GHG releases from melting permafrost and hydrates, and other such factors?

    I can’t imagine it including the “AC” feedback loop — people buying and using air conditioners a lot more in a warming climate, mainly using coal-powered electricity to run them, causing greater CO2 emissions, causing greater warming, causing still greater AC use. Of course, this would be offset somewhat by the negative feedback of less gas and electric heater use.

  15. 65
    Robin Johnson says:

    #62: Ah. I see what you were saying. Certainly, taiga and heavy brush is going to absorb more light than pathetic tundra plants and grasses. And that’s what we expect to happen as things warm up. Obviously, I agree with that.

    Robin

  16. 66
    Hank Roberts says:

    Petefontana, you wrote:

    > West Antarctic Ice Sheet is part of an overall climate
    > “tipping point.” I have heard that is supposed to be
    > reached by December 6, 2015.

    It seems you are the one to put that on the Internet for the first time. Where did this story reach your ears? It looks like a joke missing the punch line.

    > the increasing cold at the poles

    What “increasing cold” do you mean? What’s your source?

    > seems strange.

    Why? Compared to what?

    The “guy I heard talking in a bar” cite is funny, the first time.

  17. 67
    Timothy Chase says:

    Robin Johnson (#56) wrote:

    But an interesting side-effect is that the leaves need to respire LESS – which means the plant loses less water which means that more CO2 makes the plants more drought tolerant. This also increases soil moisture and reduces plant take up of rainfall.

    Yes, in fact we have seen this in the paleoclimate record and it has helped us identify the levels of carbon dioxide in earlier climates. But how quickly they will adapt depends upon the species of plant. With some plants it has to evolve. In others it is developmental. But higher levels of carbon dioxide may also decrease nutritional value.

    The Paleoclimate Record

    One of the ways that we can measure the level of carbon dioxide in earlier periods is by measuring the size of the stomata and and their number. Fewer and smaller stomata imply higher levels of carbon dioxide.

    Waiting for an Evolutionary Adaptation

    The experiments to date indicate that some plants do not automatically adjust themselves to increased levels of carbon dioxide. It has to evolve.

    For one of the studies showing that some would have to evolve this adaptation, please see:

    Effect of Elevated CO2 on Stomatal Size and Distribution in Perennial Ryegrass (html abstract only – despite the file extension)
    G. J. A. Ryle and J. Stanley
    Annals of Botany 69: 563-565, 1992
    http://aob.oxfordjournals.org/cgi/reprint/69/6/563.pdf

    Not that difficult on evolutionary scales I would presume. Several different species of ice fish have evolved antifreeze independently of one another and even to the point that they have made their blood less viscous by losing the ability form red cells as mere water has the capacity to carry sufficient oxygen at lower temperatures.

    This would have to have evolved since the last hot house and probably evolved in previous eras as well. Once they lose the ability to form red cells, the genes responsible for red blood cells mutate to the point that they will be unable to evolve back – as this is a great deal more complex than decreasing the size or number of stomatas. These fish would likely go extinct even if climate change were particularly slow – once the temperature of the Arctic and Antarctic Oceans rise above the level that the water is unable to carry sufficient oxygen.

    However, there are many plants we won’t see adapt in this fashion any time soon. Unlike our circulatory systems which adapt to thinner air at higher altitudes, the ability to developmentally adapt to higher concentrations of CO2 just isn’t there.

    Developmental Adaptation

    Others plants show different developmental strategies, increasing size (stomatal index), number (density) or epidermal cells size of stomatas. These are part of their developmental programming, similar to our adjusting the number of capillaries at different altitudes – probably for the same reason as this would result in their ability to better adapt to different altitudes, increasing the range of the species or subspecies.

    Please see:

    Stomatal Characteristics of Four Native Herbs Following Exposure to Elevated CO2 (html abstract only)
    Rachel Ferris and Gail Taylor
    Annals of Botany 73: 447-453, 1994
    http://aob.oxfordjournals.org/cgi/content/abstract/73/4/447

    Lower Nutritional Value

    Another thing to keep in mind: some plants will simply grow more quickly. However, this isn’t necessarily a good thing: in experiments performed by the Chinese with rice and wheat it nearly eliminates any gains with rice that would result from “CO2 fertilization,” and results in losses with wheat. These are main staples for much of the world’s population.

    Please see:

    Rising carbon dioxide could make crops less nutritious (Non-tech.)
    Jia Hepeng
    4 March 2005
    http://www.scidev.net/News/index.cfm?fuseaction=readNews&itemid=1969&language=1

    Responses of rice and winter wheat to free-air CO2 enrichment (China FACE) at rice/wheat rotation system (abstract)
    Ma, Hongliang et al
    Plant and Soil, Volume 294, Numbers 1-2, May 2007 , pp. 137-146(10)
    http://www.ingentaconnect.com/content/klu/plso/2007/00000294/F0020001/00009241

    However, lanthanum (the element with atomic number 57) may be used to slow the growth of rice and thereby regain some of the nutritional value.

    Please see:

    Influence of Lanthanum on Phosphorus Uptake and Its Chemical Fractions in Rice Crop (Oryza Sativa) [translated abstract]
    Xie Zubin, et al
    [A Chinese periodical, the name of which is untranslated](2003)
    http://scholar.ilib.cn/Abstract.aspx?A=zgxtxb-e200302021

  18. 68
    Robin Johnson says:

    Re #67: No need to provide information on CO2 fertilization. I’m a plant growing aquaticist – who does NOT use CO2 fertilization but whose tank is overrun with plants anyway – mainly because I use a wet-dry filtered reef tank with a closed top where the water is mixed with air in large quantities in the sump keeping the amount of CO2 and O2 at optimal levels. Stagnant plant tanks (the usual kind) lose CO2 and O2 because the water is warm with little mixing. As I pointed out in my previous post, CO2 is not a limiting factor for most plants (vines apparently benefit).

    While I am deathly concerned about Global Warming and its destructive effects – and quite frankly I think we’re fubar, ecosystems change VERY rapidly over decadal time scales. Until the 1940s, the DOMINANT tree in the Eastern US was the Chestnut. They are all gone due to a fungal disease. The Eastern US is still heavily forested. Forests in the African savannah region come and go quickly. Plants are just waiting to take advantage of a changed ecosystems. Drier conditions in many areas will turn forests into grasslands and wetter, warmer conditions will change grasslands into forests. I’m not assuming all will be “well” – not at all. I suspect things will be *bad*.

    And its a fact that many non-crop plants DO use less water with higher CO2 (but the effect is not linear for obvious reasons). And evolution “happens” damn quickly despite the way its taught (or not taught) in schools – because the traits are ALREADY there waiting to be exploited. Developing traits those don’t exist in a plant genus or family is obviously harder and takes longer timescales.

  19. 69
    David B. Benson says:

    Tjahjokartiko Gondokusumo (51) — There are at least two CHP reported upon in

    http://biopact.com

    which use biomass to produce bioenergy and either process heat or else electicity. For the one in the The Netherlands, on that site the search term biocoal should find the report. The other is on the German-Polish border and the process heat is used to heat nearby houses.

    People at Biopact are likely to prove quite helpful to you if you choose to contact them via their site.

  20. 70
    Timothy Chase says:

    Charles Muller (#58) wrote:

    #34 Timothy, #27 Pascal, #19 Karen

    Thank you for your answers…

    Uncertainties: Additive or Canceling?

    Charles Muller (#58) wrote:

    There’s no real progress in our evaluation of climate sensitivity, rather the demonstration that real progress will be very difficut to reach (worse even, the range should enlarge as we include more and more parameters for evaluation of f, so more and more uncertainty because each new parameter will have its own distribution of probability).

    According to them there has been no progress.

    Annan and Hargreaves (2006) argue that Bayesian analysis has narrowed the range of Charney climate sensitivity considerably – and that it is about 3 C. In part this is due to the climate record. However, studies as far back as the 1960s have shown that an estimated Charney climate sensitivity of about 3 C seems about right, so I guess you could say that there has been no progress. What Gerard Roe and Marcia Baker specifically reference is th 5700 multi-ensemble by climateprediction.net which is notorious for its wide spread of values. However, they also cite a variety of studies in which the upper or lower limits are wide – where some are empirical. I don’t know which ones.

    While Annan and Hargreaves gave an upper limit (at 5%) of 4.5 C, Annan suggests that this is actually being generous with the uncertainty in his blog – not that this matters so much until the technical paper comes out which demonstrates a narrower range. But for me, the question is whether Bayesian analysis may narrow the range. Annan suggests it can, in a way that is somewhat analogous to the number of surface stations increasing the accuracy of our estimation of the global average temperature and its trendline.

    The Iris Effect

    Charles Muller (#58) wrote:

    Concerning the CS from an empirical /physical perspective, there would be much more to say. For example, Spencer et al 2007 analysis of recent and precise climatologies suggests that the iris effect is not dead, after all, and the order of magnitude of the negative feedback (-6W/m2 TOA for warm tropical events) is interesting. Fortunately, the scientific research is still open and all hypothesis need to be carefully adressed.

    Well, it is a different sort of iris effect from that which was originally proposed: the pupil becomes more dilated with increased infrared rather than more constricted. Or should we now call it the retina effect? But of course retinas don’t shrink, do they? It was demonstrated that the tropical clouds which would be subject to the iris effect tend to increase the strength of the greenhouse effect, but the empirical study which you have cited demonstrates that these clouds become less common. Or is it possible that they become more spread out? I am thinking of the twilight effect where there is an invisible extension to clouds extending for tens of kilometers.

    May 3, 2007
    Widespread Twilight Zone Detected Around Clouds
    http://earthobservatory.nasa.gov/Newsroom/NasaNews/2007/2007050324883.html

    On the twilight zone between clouds and aerosols (abstract)
    Ilan Koren, et al
    18 April 2007
    Geophysical Research Letters, Vol. 34, L08805, doi:10.1029/2007GL029253, 2007
    http://www.agu.org/pubs/crossref/2007/2007GL029253.shtml

    This might be a way of explaining the results which show a clear sky super greenhouse effect in which downwelling thermal radiation from the atmosphere increases more rapidly in the tropics than upwelling thermal radiation at sea surface temperatures (SSTs) above 300 K, occuring over 52 % of the tropics between 20 N and 20 S between the years of 1985 to 1989.

    Please see:

    Direct Radiometric Observations of the Water Vapor Greenhouse Effect Over the Equatorial Pacific Ocean
    Francisco P. J. Valero, et al
    Science Vol 275 Mar 1997, 1773-1776
    http://www.sciencemag.org/cgi/content/full/275/5307/1773

    It is after all clouds in the tropics which show the “negative feedback” of “fewer” clouds. And I suppose if we aren’t talking about the twilight effect, then the negative feedback won’t be that negative if the clear sky greenhouse effect is becoming stronger with higher temperatures. So in this sense the inverse “iris effect” is quite dead to the extent that it might be regarded as contributing a significant negative feedback in the tropics. The form that Spencer (2007) brings up would appear to be overwhelmed by the super greenhouse effect which we have been aware of since 1997.

    Are the Models Improving?

    I would also keep in mind the fact that the more physics we include in the models, the more accurate they become — at least in terms of being able to model the climate system. Gavin Schmidt has said as much and I would presume that he would know. Given that models have been improving in their ability to model processes, I personally find it difficult to believe that, at least in terms of a Bayesian analysis, the models themselves aren’t doing better in terms of their ability to identify climate sensitivity by applying first principles to our climate system.

    I would also keep in mind the fact that we are only speaking of the short-term Charney Climate Sensitivity, and the long-term climate sensitivity is presumably going to be about twice that – due to ice sheet loss and the like.

    Please see:

    Hansen, J., Mki. Sato, P. Kharecha, G. Russell, D.W. Lea, and M. Siddall, 2007: Climate change and trace gases. Phil. Trans. Royal. Soc. A, 365, 1925-1954, doi:10.1098/rsta.2007.2052
    http://pubs.giss.nasa.gov/abstracts/2007/Hansen_etal_2.html

    But I suppose this may involve the longer tail which people are worried about. Then again, if Roe and Baker are including multiple studies, this might also explain some of the uncertainty which they are seeing as they could be conflating short-term (~3 C) and long-term (~6 C) climate sensitivities. Hansen (2007) suggests that the climate records involving Antarctica do a fairly good job of narrowing the range on the long-term climate sensitivity – and studies of present day climate change would remain silent for the most part as the long-term feedback has only begun to kick in.

    The big question for Hansen is of course how quickly these long-term feedbacks will take to manifest themselves, and given what we are now seeing as well as the paleoclimate record itself, it seem that the answer is sooner rather than later. Especially since black carbon wasn’t as much of an issue in previous instances of global warming and is now becoming an issue again as the result of economic development in China. Of course we may also want to keep in mind the higher rates of carbon emissions since 2000 – which weren’t included in IPPC R4 projections. If I remember correctly, they’ve tripled.

    Anyway, hope this helped…

  21. 71
    Ray Ladbury says:

    Re #61
    SCM, all the group are saying is that you have to consider the actual probability distribution, and for ill-behaved distributions it is quite possible to have more probability above 2x the mode than below the mode. Consider the Pareto distribution, which is used to fit percentile wealth vs percentile population as an example.

  22. 72
    Charles Muller says:

    #70 Timothy

    Thank you for the references.

    The 2,1-4,4 °C range of IPCC 2007 (with 3°C as best estimate) is equilibrium (long term) sensitivity. Transient climate response for 2xCO2 is rather 1,0-2,6°C. So, I don’t know what you mean exactly when you suggest a long-term climate sensitivity twice more important.

  23. 73
    Phil Scadden says:

    Can I seek a clarification here? I understand that climate sensitivity is temperature response to change in atmosphere CO2 concentration, not a response to change to man-made CO2 emission. So feedbacks like reduced ocean capacity, changes due to landuse etc. might effect our ability to predict future CO2 levels for a given anthropogenic input, but they are irrelevant to the sensitivity of T to actual CO2 concentration. From the straight physics, surely the only feedbacks that affect the sensitivity are albedo, cloud effect (both positive/negative) and water vapour? Any others? Correct me if I am wrong too, but I thought GCMs were calculating T directly rather than parametizing through S? Ie I would expect S to output of a GCM not an input?

  24. 74
    Timothy Chase says:

    Charles Muller (#72) wrote:

    #70 Timothy

    Thank you for the references.

    The 2,1-4,4 °C range of IPCC 2007 (with 3°C as best estimate) is equilibrium (long term) sensitivity. Transient climate response for 2xCO2 is rather 1,0-2,6°C. So, I don’t know what you mean exactly when you suggest a long-term climate sensitivity twice more important.

    I didn’t say twice as important – as that would be a normative issue. Is what happens as the result of slow feedback important? Well, I guess it depends upon your standards. But in terms of the rise in temperature it would seem to be twice as high.

    But why?

    Essentially Charney climate sensitivity is calculated only with the fast feedbacks: water vapor, sea ice, etc. What it ignores are the slow feedbacks from the ice sheets and the carbon cycle itself — as it treates both as boundary conditions. For example, it treates ice sheets as a boundary condition and therefore ignores the fact that over time the ice sheets respond, amplifying the effects our of anthropogenic pulse of carbon dioxide.

    Likewise, when treating carbon dioxide simply as a forcing rather than our anthropogenic greenhouse gas emissions, it omits the fact that it is a pulse which may later be subject to feedback from the carbon cycle itself — which will amplify the greenhouse effect of the original pulse and likewise the effects of changes to the ice sheets.

    Now what do we mean by the slow feedbacks being “transient”?

    Pretend for a moment that we double the amount of carbon dioxide with our emissions. Seems rather likely to me, actually. First doubling. In the shortrun this raises the temperature best estimate 3 C. Afterwards the ice sheets melt. To keep things simple, we will say that all of the ice sheets melt and that they are responsible for all the slow feedback, but this does nothing more than double the effects upon temperature of the original pulse. Now we are at 6 C.

    By transient does this mean that as soon as the ice sheets are gone we drop back to 3 C?

    “Yes” in terms of climate sensitivity but “no” in terms of temperature.

    Yes in the sense that if we double the CO2 again this will simply bring us up to 9 C. No in the sense that simply keeping the CO2 at the first doubling will not cause the temperature to drop back down to 3 C. The climate sensitivity may very well be transient (dropping from 6 C per doubling down to 3 C per doubling after the ice sheets are gone), but this does not mean that whatever degrees we gain while it exists are suddenly lost any more than that the ice sheets will suddenly reappear once they have melted. Once the ice sheets are gone, they will be gone for a very long time. While they are gone for how ever many millenia the climate system will be absorbing more sunlight, and more thermal radiation will be produced. The “transient” nature of the slow feedbacks in no way changes this.

    Anyway, that is my understanding of the treatement of this issue in:

    Hansen, J., Mki. Sato, P. Kharecha, G. Russell, D.W. Lea, and M. Siddall, 2007: Climate change and trace gases. Phil. Trans. Royal. Soc. A, 365, 1925-1954, doi:10.1098/rsta.2007.2052
    http://pubs.giss.nasa.gov/abstracts/2007/Hansen_etal_2.html
    pg. 1944

    To what extent does the IPCC treate this issue?

    I honestly do know. However, we do know how they have dealt with the rise in sea level – and they limit their projections to the first century – as a steadfast rule, I believe. This would suggest to me that they aren’t really dealing with the issue of the “constant boundary conditions” for Charney-type analysis changing as a form of slow feedback. However, I believe the climatologists here might be in a better position to say.

  25. 75
    Timothy Chase says:

    Phil Scadden (#73) wrote:

    Can I seek a clarification here? I understand that climate sensitivity is temperature response to change in atmosphere CO2 concentration, not a response to change to man-made CO2 emission. So feedbacks like reduced ocean capacity, changes due to landuse etc. might effect our ability to predict future CO2 levels for a given anthropogenic input, but they are irrelevant to the sensitivity of T to actual CO2 concentration.

    So you would think.

    Certainly in terms of the underlying physics it is irrelevant whether it comes from us or various feedbacks from the carbon cycle. However, in terms of the fast-feedback Charney analysis, changes in CO2 is treated simply as a forcing being applied from to system from “outside” of the climate system, and as a forcing it is not viewed as feedback – at least according to Hansen (2007) – see above.

    But why take his word for for it? This is after all the fellow who if given 50 cm will take 5 m.

    So decided to check with the IPCC itself. Apparently he’s right.

    Please see:

    The coupled climate carbon cycle intercomparison project (C4MIP) will permit the assessment of model sensitivity of the carbon cycle to global temperature change. The carbon cycle feedback is potentially important to 21st century climate projections, but is not conventionally included in the climate sensitivity as it is not a fast feedback.

    IPCC Working Group I – Workshop on Climate Sensitivity, Workshop Report
    École Normale Supérieure, Paris, France
    26–29 July, 2004
    pg 11

  26. 76
    Ike Solem says:

    A few comments on some issues raised in comments (#1, #2, #7, #11, #15, #47, #52, #73) on the nature of “S”:

    (1)From the paper: “Climate consists of a set of highly coupled, tightly interacting physical processes.”

    Physical in the academic sense? If so, I think we want to include tightly coupled chemical and biological processes, in that case – for example, the chemical fate of atmospheric methane over time, the effects of increasing atmospheric CO2 on oceanic acid-base chemistry, and the response of the biological components of the carbon cycle to increased temperatures and a changing hydrologic cycle.

    (2)From the paper: “Because we are considering an equilibrium temperature rise, we consider only time-independent processes.”

    The transient responses are of great concern. The difference between a slow transition and a fast transition to a new equilibrium position has at least two important effects: the rate of sea-level rise due to the speed at which ice sheets melt, and carbon-cycle feedback effects including a melting Arctic permafrost and potential destabilization of oceanic methane hydrates. Others include the ability of the biota to respond to new circumstances in a timely manner (the extinction issue) and the rate of change of the hydrologic cycle (which are linked).

    (3) From the supporting perspective article: “All this would be very bad news if avoiding dangerous anthropogenic interference in the climate system required us to specify today a stabilization concentration of carbon dioxide (or equivalent) for which the risk of dangerous warming is acceptably low. Fortunately, we do not need to.”

    That seems to assume a large degree of human control over carbon-cycle feedback processes and the ability to stabilize at some future point. Sometimes, when a fire gets big enough you can’t put it out (for example, consider the wind-driven wildfires in Southern California). Then you have the ice sheet dynamics issue.

    (4) From the above post: “Annan and Hargreaves (2006) used a Bayesian statistical approach that combines information from both 20th century observations and from last glacial maximum data to produce an estimate of climate sensitivity that is much better constrained than by either set of observations alone.”

    What’s the main difference between the past few million years of the glacial-interglacial cycle and the present? It seems that it is that the net size of the active carbon pool has increased by a fair amount relative to the glacial-interglacial pool due to transfer of fossil carbon to the atmosphere, and hence slowly to the oceans. What I’m wondering is if our activities could actually be putting an end to the past few million years of the interglacial-glacial cycle and return to the conditions that existed around 4 million years ago?

    What if atmospheric CO2 accumulation starts accelerating due to natural chemical-biological feedbacks due to warming oceans and land masses? What if the IPCC “business-as-usual” scenario is a large underestimate of the rate of increase of atmospheric CO2? No change in the equilibrium sensitivity to 2X CO2, but the transient response could be pretty rough.

    (5) From the above post: “However, in our view, Allen and Frame’s discussion turns the precautionary principle on its head by implying that downward revision can always be done later, after more data are in. But a good adaptive strategy depends on nimble action and forward thinking. . .” Yes! Well put.

  27. 77
    Dave Rado says:

    Re. #59, petefontana:

    I certainly hope hundreds of millions of people are not overly dependant on glacier fed water supplies. If they are, was this ever a good idea?

    Those glaciers (and the summer melt water they supply) have been there for the entire existence of human civilisation, so you may as well ask whether human civilisation was ever a good idea.

    Lynn Vincentnathan wrote in #63:

    A large chunk of humanity is dependent on glacier melt (also snowpack melt — e.g., I think in the U.S. west). This includes among other peoples 40% of India’s and China’s populations, which comes to 500 million people, but doesn’t include the many millions of glacier-dependent people elsewere.

    All of the “Stans” (Pakistan, Uzbekistan, Turkmenistan, etc.) are also dependendant on glacier melt, as are most of the Andean countries in South America (e.g. see here , here and here).

  28. 78
    Steve Bloom says:

    Re #58: “Spencer et al 2007 analysis of recent and precise climatologies suggests that the iris effect is not dead, after all.” While there seems to be mounting evidence that Spencer must have studied some field other than climatology, I doubt that it was necromancy. Embalming, maybe. :) How many times do Spencer and Christy have to be proven wrong before people like you stop uncritically quoting their results?

    The science involved with the “iris” idea being quite difficult for laypeople, whenever the subject comes up I tend to resort to asking how the glacial cycles (and paleoclimate generally) can be explained if there really is an effect that damps sensitivity to that extent. I’m still waiting for an answer.

  29. 79
    Charles Muller says:

    Timothy @74

    “Now what do we mean by the slow feedbacks being “transient”?
    Pretend for a moment that we double the amount of carbon dioxide with our emissions. Seems rather likely to me, actually. First doubling. In the shortrun this raises the temperature best estimate 3 C. ”

    See Table 8.2, chap. 2, IPCC 2007 :
    http://ipcc-wg1.ucar.edu/wg1/wg1-report.html

    The mean transient climate response for 2xCO2 is something like 1,7 °C. That’s what you call fast feedbacks response (water vapour, lapse rate, nebulosity, etc.)

    But 3,2°C is the best estimate for equilibrium climate sensitivity (that is when the runs of models consider all the feedbacks).

    Some AOGCM models have been coupled with carbon cycle models, but I’ve not yet regained the exact references concerning this coupling and the results for the range of equilibrium CS.

  30. 80
    Dave Rado says:

    Re. the Roe and Baker paper, William Connolley is dubious.

    As William says in his post, it’ll be interesting to see what James Annan thinks about it (I imagine he’s working on a post about it).

    [Response:I asked Gerard Roe to respond to William’s concern, which is about the assumption that f is Gaussian. I posted his response (comment #6 below William’s blog entry), which ought to clear this up.–eric]

  31. 81
    Patrick Henry says:

    During the Jurassic, CO2 concentrations were at least 2000ppm higher than they are now, and temperatures were about 10C higher. So how does a 70ppm rise in CO2 produce a 4.5C increase in temperature? The models are overestimating temperature rise by an order of magnitude.

    It is important to occasionally correlate computer models with the historical record, otherwise they produce nothing but GIGO.

    [Response: Huh? 4.5C is a high estimate for doubling CO2 (i.e. an extra 280 ppm). Plus estimates of anything from the Jurassic are highly uncertain. – gavin]

  32. 82

    Eric;
    Pat Michaels seems perfectly certain the ENSO is decoupled from temperature trends , and constant even over geological deep time . It would be interesting to see if his publisher will accept feedback from RC-
    http://www.spectator.org/dsp_article.asp?art_id=12225
    “The Fires This Time
    The American Spectator
    Patrick J.Michaels 10/29/2007

    “Blame California’s mega-fires on global warming. Or at least that’s what Senate Majority Leader Harry Reid (D-NV) said last week in the Hill.

    Global warming affords endless opportunities to test glib hypotheses by politicians who have no training whatsoever in fields of which they claim pontifical knowledge. And Reid’s statement is easy to test…California’s big wildfires are, ironically, caused by excessive winter rains. The more it rains in the winter, the more vegetation grows, and the more there is to burn in the summer, which is invariably hot and dry.

    Some of the very wet years are caused by El Nino, a reversal of winds over the Pacific Ocean that has been going on every few years ever since there was a Pacific Ocean…People… will cite computer models predicting that El Ninos should become stronger or more frequent with global warming, but there are an awful lot of other models showing that they won’t change or that they might even lessen in frequency. The Nobel Prize-winning United Nations Intergovermental Panel on Climate Change says “There is no consistent indication of discernible future changes in ENSO [an acronym for El Nino] amplitude and frequency.”

  33. 83
    Timothy Chase says:

    Re Charles Muller (#79) on climate sensitiviy, transient climate response, and slow versus fast climate feedbacks (with a focus on the carbon cycle)

    Or “Will a doubling of CO2 raise the average temperature by 3 C or 6 C?”

    **

    Charles, what I will argue is that there are two equilibria that need to be considered: that resulting from the fast feedbacks and that which results from all feedbacks. For the most part, the IPCC is concerned only with the fast feedbacks – although I will note below where this is changing. The “transient climate response” and transient climate sensitivity still refer to the fast feedbacks, of course. But so does the equilibrium climate sensitivity, only after the forcing ceases, e.g., we quite raising CO2 concentrations with our emissions.

    The Meaning of Transient Climate Response

    Charles Muller (#79) wrote:

    See Table 8.2, chap. 2, IPCC 2007 :
    http://ipcc-wg1.ucar.edu/wg1/wg1-report.html

    The mean transient climate response for 2xCO2 is something like 1,7 °C. That’s what you call fast feedbacks response (water vapour, lapse rate, nebulosity, etc.)

    Different beast, then. I had inadvertently misused the term “transient climate response” given the term “transient.” In a sense, the higher climate sensitivity associated with the slow feedbacks are transient, but the transient response and equilibrium response both refer to the fast feedbacks, not the slow feedbacks.

    What is meant by the “Transient Climate Response”

    In the “transient climate response,” we still aren’t talking about positive feedback from the carbon cycle, but we aren’t exactly talking about a single pulse of additional carbon dioxide, either. To let people see what we are talking about, let’s go to 2001 since that is up on the web as a webpage:

    Climate Change 2001:
    Working Group I: The Scientific Basis
    http://www.grida.no/climate/ipcc_tar/wg1/345.htm

    As we raise the level of carbon dioxide by means of our emissions, the temperature rises. When we stop raising the level of carbon dioxide, the temperature continues to rise because it takes a while for the climate system to reach equilibrium. Partly this is due to the thermal inertia of the ocean, the fact that it takes while for the stratosphere to expand and then finally warm to its equilibrium level.

    For the moment, lets just go into the evolution of the stratosphere under an enhanced greenhouse effect – assuming a single pulse of carbon dioxide. The stratosphere first cools due to reduced longwave, then the surface and lower atmosphere rise in temperature, the troposphere expands and expands the stratosphere with it, further cooling the stratosphere. Then as the troposphere warms, more longwave escapes to the stratosphere, warming the stratosphere, although it will still be cooler at the end of the process than at the beginning.

    That takes time. So does the warming of the ocean, or for that matter, even the water vapor feedback as the increasing partial pressure water vapor is both a response to higher temperatures and a cause of higher temperatures – but can raise temperatures only against the thermal inertia of the ocean. As such, when emissions quit raising the temperature, it will still take a considerable amount of time for the system to reach equilibrium.

    Does the IPCC’s “Equilibrium Climate Sensitivity” Include All Feedbacks?

    Charles Muller (#79) wrote:

    But 3,2°C is the best estimate for equilibrium climate sensitivity (that is when the runs of models consider all the feedbacks).

    No, I am afraid not.

    Even at this point, the equilibrium is still one that is based on fast feedbacks, not the slow feedbacks involved in either the carbon cycle or ice sheets – as these would be assumed constant by the Charney analysis of climate sensitivity.

    This is most easily seen in AR2, but it still applies (more or less) to AR4 — as I will show shortly.

    For AR2, please see:

    2.3.3 Climate Sensitivity: Definition

    The term “climate sensitivity” refers to the steady-state increase in the global annual mean surface air temperature associated with a given global mean radiative forcing. It is standard practice to include only the fast feedback processes, including changes in water vapour, in the calculation of climate sensitivity, but to exclude possible induced changes in the concentrations of other greenhouse gases (as well as other slow feedback processes).

    An Introduction to Simple Climate Models used in the IPCC Second Assessment Report (1997), pg 12
    http://www.ipcc.ch/pub/IPCCTP.II(E).pdf

    But that was 1997.

    Preparing for AR4

    Let’s look at something a little later, something done in preperation for AR4 – plans testing the incorporation of the carbon cycle into climate models. It specifically states that climate sensitivity does not conventionally include carbon cycle feedback as it is “not a fast feedback.”

    Please see:

    The coupled climate carbon cycle intercomparison project (C4MIP) will permit the assessment of model sensitivity of the carbon cycle to global temperature change. The carbon cycle feedback is potentially important to 21st century climate projections, but is not conventionally included in the climate sensitivity as it is not a fast feedback.

    IPCC Working Group I – Workshop on Climate Sensitivity, Workshop Report
    École Normale Supérieure, Paris, France
    26–29 July, 2004
    pg 11

    Incidentally, the intercomparison project was completed – but we will get to that in a moment.

    Climate Sensitivity in the AR4 Glossary

    Looking at the glossary entry for “climate sensitivity” (which is too long to quote but the location of which is clearly identified in the table of contents) in AR4 WG1 (2007) suggests that nothing has changed in this regard.

    *

    Chapter 8 of WG1 AR4

    Looking at the Chapt 8 Executive Summary, we find that they are merely exploring the potential importance of carbon cycle feedbacks.

    Please see:

    Chapter 8, Executive Summary

    To explore the potential importance of carbon cycle feedbacks in the climate system, explicit treatment of the carbon cycle has been introduced in a few climate AOGCMs and some Earth System Models of Intermediate Complexity (EMICs).

    AR4WG1, Chapt 8 (2007), pg. 591

    *

    They are considering the addition of some components of the carbon cycle into models (notably the faster biological components), but these are not yet routinely incorporated into the models used for making climate projections.

    Please see:

    8.2.3.1 Surface Processes

    The addition of the terrestrial biosphere models that simulate changes in terrestrial carbon sources and sinks into fully coupled climate models is at the cutting edge of climate science. The major advance in this area since the TAR is the inclusion of carbon cycle dynamics including vegetation and soil carbon cycling, although these are not yet incorporated routinely into the AOGCMs used for climate projection (see Chapter 10).

    AR4WG1, Chapt 8 (2007), pg. 604

    *

    Furthermore, there has been only one systematic evaluation of carbon models that were coupled to climate models.

    Please see:

    8.3.4.3 Surface Fluxes

    The only systematic evaluation of carbon models that were interactively coupled to climate models occurred as part of the Coupled Climate-Carbon Cycle Model Intercomparison Project (C4MIP), where Friedlingstein et al. (2006) compared the ability of a suite of models to simulate historical atmospheric CO2 concentration forced by observed emissions. Issues relating to the magnitude of the fertilization effect and the partitioning between land and ocean uptake were identifi ed in individual models, but it is only under increasing CO2 in the future (see Chapter 10) that the differences become large. Several other groups have evaluated the impact of coupling specific models of carbon to climate models but clear results are difficult to obtain because of inevitable biases in both the terrestrial and atmospheric modules (e.g., Delire et al., 2003).

    AR4WG1, Chapt 8 (2007), pg. 618

    The systematic study to which they are refering is:

    Climate–Carbon Cycle Feedback Analysis: Results from the C4MIP Model Intercomparison (abstract)
    P. FRIEDLINGSTEIN,et al
    Journal of Climate, Vol 19, 15 Jul 2006
    http://nora.nerc.ac.uk/327/

    This is the C4MIP Intercomparison study mentioned above. I would certainly recommend it.

    *

    In any case, it would appear that they are testing the waters, but they have not incorporated the carbon cycle as of yet. Such tests are merely experimental, tentative, and are not routinely included in climate projections – any more than ice sheets are. As such, even in the case of the carbon cycle, it would appear that WG1 AR4 deviated very little if at all from fast feedback Charney climate sensitivity.

    Thus when they make projections of 3 C per doubling, this is not taking into account slow feedbacks – which (according to Hansen’s analysis) double the long term climate sensitivity.

  34. 84
    Timothy Chase says:

    Correction to 81, response to Charles Muller regarding climate sensitivity and transient climate response…

    In the paragraph summarizing the inertia of the climate system in the context of fast feedbacks:

    That takes time. So does the warming of the ocean, or for that matter, even the water vapor feedback as the increasing partial pressure water vapor is both a response to higher temperatures and a cause of higher temperatures – but can raise temperatures only against the thermal inertia of the ocean. As such, when emissions quit raising the temperature, it will still take a considerable amount of time for the system to reach equilibrium.

    The last sentence should read:

    As such, when emissions quit rising, according to their framework, the climate system is no longer being forced, but the temperature will continue to rise and it will still take a considerable amount of time for the system to reach equilibrium.

  35. 85
    Anders Lundqvist says:

    What is “relative probablity”? (The y-axis in the chart.)

  36. 86
    Charles Muller says:

    #78 David wrote :
    “How many times do Spencer and Christy have to be proven wrong before people like you stop uncritically quoting their results?”

    Quite simple: as long as they publish in peer-review scientific literature rather than necromancy magazines. Of course, you’re free to ignore their climatologies, enact there’re a priori wrong and consider tropical warm events of the recent years have produced positive feedbacks TOA. Something like: “Some UAH team data have been corrected in the past, so UAH team data are false by nature and will be corrected in the future”. This kind of inductive assumption is a strange basis for the critical thinking you advocate, no ?

  37. 87
    pete best says:

    Dear RC, Is it not possible that scientists and mathematicians from the science of non linear dynamics (which maths I am presuming is being used in the maths of climate models)to shed light on the amplification and dampening of the climates feedback cycles and hence the so called “sensitivity” issue and hence the possible range of temperatures ?

    Real climate has forever stated that Delta is going to be 3 C with a atmospheric doubling of pre industrial CO2 levels but now lots of people are suggesting that 450 ppmv has a high probability of reaching 2C of warming which because of sinks becomming sources at this temperature level presupposses 3C due to this high level of positive feedback?

    450 ppmv is some 30-40 years away. Is this the current scientific nad political slant on this subject ?

  38. 88

    [[Please, please show me just one quantitative paper where a doubling of atmospheric CO2 produces a temperature change of X or Y degrees, even if it’s negative. ]]

    Try here:

    http://members.aol.com/bpl1960/ClimateSensitivity.html

  39. 89

    [[Some prominent individuals have suggested that the disintegration of the West Antarctic Ice Sheet is part of an overall climate “tipping point.” I have heard that is supposed to be reached by December 6, 2015.]]

    I don’t see how anybody could predict it that exactly.

  40. 90
    Nick Barnes says:

    Patrick Henry @81: ~2000ppm is three doublings from the pre-industrial 280 ppm. So, if accurate, a measured 10C at 2000ppm would be confirmation of a ~3C sensitivity.

    This is trivial arithmetic.

    However, the Jurassic is basically irrelevant to the modern climate because *everything* was different then (for a very abbreviated list: solar intensity, atmospheric composition, locations of continents, oceans, and climatic zones, axial tilt, orbital dynamics, photosynthetic species). So even if we had accurate data on CO2 and temperature from the Jurassic, we could not deduce anything from them about modern CO2 sensitivity.

  41. 91
    Nick Barnes says:

    Patrick Henry @81: and describing the Jurassic as part of “the historical record” must be some new use of the word “historical” of which I was not previously aware.

  42. 92
    J.C.H. says:

    Charles Muller Says:
    29 October 2007 at 4:49 AM
    #78 David wrote :
    “How many times do Spencer and Christy have to be proven wrong before people like you stop uncritically quoting their results?”

    “Quite simple: as long as they publish in peer-review scientific literature …”

    I read their most recent paper. On RC somebody asked about it a few weeks ago. I don’t think anybody responded to the question.

    Quoting from the paper:

    “This decrease in ice cloud coverage is nominally supportive of Lindzen’s ‘‘infrared
    iris’’ hypothesis. …”

    I think I’ve seen that overstated a tad on the more politically inclined blogs.

  43. 93
    Charles Muller says:

    #83 Timothy

    Thank your your precisions and references. If I summarize, the main issue seems the long term feedbacks due to carbon cycle evolution under warming conditions. According to Friedlingstein 2006, the 11 models of CMPIP-M-4 presently conclude to a positive feedback, with (A2 SRES) +20-200 ppm CO2 and +0,1-1,5°C for 2100. These additional feedbacks are not still accounted by GCM models, at least those used in IPCC 2007 for equilibrium climate sensitivity.

    Well, that is an interesting point for the next few years of research (and so the future IPPC AR5). The wide range of the 11 models (factor 10 for additional CO2 atm. concentration) shows that modelization of the physical and biological processes underlying the carbon cycle is still in its infancy.

    What I still miss is, for climate sensitivity at 2xCO2 (540 ppm) we’re discussing here, how you “jump” from a best estimate of 3°C to 6°C. The A2 SRES used by Friedlingstein 2006 go far over the doubling (856 ppm for CO2, but also 3731 ppb for CH4, and, with all other GHGs + negative forcing integrated, a 8,07 W/m2 forcing very different of the 3,7 W/m2 for the sole 2xCO2 used to estimate CS). In spite of this, the worse estimate from CMPIP-M-4 is “just” +1,5°C (I ignore the mean value of the distribution).

  44. 94
    Charles Muller says:

    #92 Spencer el al 2007 paper doesn’t really support the precise mechanism proposed by Lindzen for Iris effect, but more simply observes a strong TOA negative correction associated with warming events at 20°S-20°N (that is : in the 2000-2005 period of observation, the most significative warming episodes of the surface + low troposphere – 40 days or more – leads to a negative SW+LW cloud forcing at the top of the atmosphere). That’s too short to infer a robust conclusion, anyway, and maybe short-term variations toward high temperature are not representative of the long-term warming induced by GHGs. But that’s an interesting piece, because lapse rate / nebulosity / water vapour feedbacks in the Tropics are still a major uncertainty (source of divergence) in models.

    [Response: Spencer et al has nothing to do with the iris effect despite their claims. Their correlations are based on a dynamic mode of variability (the Madden-Julian Oscillation) which has nothing to do with any SST forced response in the clouds. It’s just a bad analogy (rather like using the day-night contrast to estimate climate sensitivity). – gavin]

  45. 95
    chris says:

    do you think the co2 is changing the external makeup of the environemntl

  46. 96
    henning says:

    #92 J.C.H.: I think I’ve seen that overstated a tad on the more politically inclined blogs.

    What’s that supposed to mean? Just because somebody quotes a statement like that to make a politically motivated point, anything supporting the iris theory (whatever one thinks about it) must be bad science?

  47. 97
    David B. Benson says:

    pete best (87) — The current CO2 concentration in the atmosphere is 384 ppm and growing at 2 ppm per year. Assuming this growth continues, the earth reaches 450 ppm in 32 years, 2039 CE.

  48. 98
    Hank Roberts says:

    http://environment.newscientist.com/article/mg19626273.300-exxons-funding-of-polar-bear-research-questioned.html

    “… researchers, including Willie Soon of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, published their findings as a “viewpoint”, which is not peer-reviewed. They conclude that the polar bears are not threatened by climate change (Ecological Complexity, DOI: 10.1016/j.ecocom.2007.03.002)….”

  49. 99

    I would like to echo Anders question in comment 85. The “relativity probability” shown on the vertical axis in the graph shows values greater than one?! How does this happen? Since the probability of an outcome is always between 0 and 1, how do they derive a probability greater than one?

  50. 100
    Lynn Vincentnathan says:

    I’ll ask it again. What do Roe & Baker include as “f” feedbacks? (I don’t have access to the article.)


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