By Dr. Pat Michaels at World Climate Report
A new, lower estimate of climate sensitivity
There is word circulating that a paper soon to appear in Science magazine concludes that the climate sensitivity—how much the earth’s average temperature will rise as a result of a doubling of the atmospheric concentration of carbon dioxide—likely (that is, with a 66% probability) lies in the range 1.7°C to 2.6°C, with a median value of 2.3°C. This is a sizeable contraction and reduction from the estimates of the climate sensitivity given by the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), in which the likely range is given as 2.0°C to 4.5°C, with a best estimate of 3.0°C.
Further, the results from the new analysis largely eliminate the “fat tail” of the distribution of possible values of the climate sensitivity (that the IPCC AR4 report was fond of) which included the possibility that very large climate sensitivities are a realistic possibility. In the new paper, the authors find only “vanishing probabilities” for a climate sensitivity value greater than 3.2°C and that values greater than 6.0°C are “implausible.”
Contrast that with the IPCC assessment of the literature (summarized in our Figure 1) which routinely includes studies concluding there is a greater than a 10% possibility that the true climate sensitivity exceeds 6°C and some which find that there is a greater than 5% possibility that it exceeds 10°C.
Figure 1. Climate sensitivity distributions retained (and in some cases recast) by the IPCC from their assessment of the literature. Note the “fat tail” towards the right which indicates the possibilities of the climate sensitivity having a very large positive value (that is, a huge degree of global temperature rise for a doubling of the atmospheric carbon dioxide concentration) (source: IPCC AR4).
The new paper, from a team of researchers led by Andreas Schmittner of Oregon State University, throws cold water on the IPCC’s tails. Here is its rather provocative abstract:
Assessing impacts of future anthropogenic carbon emissions is currently impeded by uncertainties in our knowledge of equilibrium climate sensitivity to atmospheric carbon dioxide doubling. Previous studies suggest 3 K as best estimate, 2–4.5 K as the 66% probability range, and non-zero probabilities for much higher values, the latter implying a small but significant chance of high-impact climate changes that would be difficult to avoid. Here, combining extensive sea and land surface temperature reconstructions from the Last Glacial Maximum with climate model simulations we estimate a lower median (2.3 K) and reduced uncertainty (1.7–2.6 K 66% probability). Assuming paleoclimatic constraints apply to the future as predicted by our model, these results imply lower probability of imminent extreme climatic change than previously thought.
Figure 2 shows the distribution of the range of the earth’s probable climate sensitivity as determined by Schmittner et al. Note the rapid drop-off in the probability that the climate sensitivity is much greater than 3°C (the IPCC “best estimate” for the sensitivity), and that the distribution falls off less slowly towards the left (towards lower sensitivity) than towards the right (higher sensitivities). The “fat right-hand tail” of the distribution is gone and the possibility that the climate sensitivity is in the 1°C to 2°C range is not minimal.
Figure 2. Distribution of the land/ocean climate sensitivity as determined by Schmittner et al. (adapted from Schmittner et al., 2011).
The Schmittner et al. results join a growing number of papers published in recent years which, by employing investigations of the earth’s paleoclimate behavior (that is, how the earth’s temperature changes in the past when subject to changing climate forcings) have come to somewhat similar conclusions, especially regarding the (lack of) evidence to support the existence of the fat right-hand tail.
For example, researchers James Annan and Julia Hargreaves published a paper in 2009 that concluded many of the assumptions underlying the possibilities of very high climate sensitivities were unjustified. They wrote:
When instead reasonable assumptions are made, much greater confidence in a moderate value for [the climate sensitivity] is easily justified, with an upper 95% probability limit for [the sensitivity] easily shown to lie close to 4°C, and certainly well below 6°C. These results also impact strongly on projected economic losses due to climate change.
Annan made repeated comments during the IPCC AR4 review process that the IPCC’s handling of climate sensitivity and its probability distributions were incorrect. His complaints largely fell upon deaf ears.
However, as there are appearing more and more examples in the literature, of which Schmittner et al. is one of them, making a convincing case that the very high climate sensitivities are not defendable, there will be growing pressure on the IPCC in its Fifth Assessment Report to greatly shrink the fat tail of the probability distribution for the true climate sensitivity. However, the climate “realists” very bad experience with the last IPCC process makes them chary. James Annan, writing at his blog in reference to the new Schmittner et al. paper had this to say as to what may result from it:
That said, [the Schmittner et al. paper] is a useful antidote to the exaggerated uncertainty estimates that have been prevalent over recent years, and I certainly applaud the intentions and effort underlying this substantial piece of work. In any case, I expect the merchants of doubt to do their worst on it when they cite it in the IPCC report.
But, as the evidence mounts against a high value for the climate sensitivity, and evidence grows for a low value (recall that the observed rate of global warming for the past several decades has fallen well below IPCC best estimates), the IPCC is going to be hard-pressed to retain the status quo in its Fifth Assessment Report, especially in light of the enhanced scrutiny that its AR4 misdeeds brought upon the process.
But, as James alludes to, perhaps we ought not be holding our breath.
And, for those keeping score out there, about 10 years ago, a couple of us here at WCR were part of a team which published a paper in the journal Climate Research in which we employed a variety of techniques to derive empirical estimates of the amount of temperature rise that we could expect by the end of this century—a rise that could pretty well be considered to be in-line with the climate sensitivity. We concluded that the expected temperature rise between 1990 and 2100 would be in the range 1.0°C to 3.0°C with our best guess being 1.8°C (in contrast to the IPCC estimates, which, at the time, were for a rise of between 1.4°C and 5.8°C).
References:
Annan, J.D., and J.C. Hargreaves, 2009. On the generation and interpretation of probabilistic estimates of climate sensitivity. Climate Change, 104, 423-436, doi:10.1007/s10584-009-9715-y, http://www.jamstec.go.jp/frsgc/research/d5/jdannan/probrevised.pdf
Michaels, P.J., P.C. Knappenberger, O.W. Frauenfeld, and R.E. Davis, 2002. Revised 21st century temperature projections. Climate Research, 23, 1-9.
Schmittner, A., et al., 2011. Climate sensitivity estimated from temperature reconstructions of the Last Glacial Maximum, Science, in press*, http://www.princeton.edu/~nurban/pubs/lgm-cs-uvic.pdf
*According to the authors
“…the IPCC is going to be hard-pressed to retain the status quo in its Fifth Assessment Report…”
Nah. They’ll just lie. No problemo. “Worse than we thought.” “Robust.” “Unequivocal.” “Must act now.”
BTW, congratulations, Vuk!
Pat Michaels quoted rather selectively from Annan’s blog post on this paper…Here is the paragraph before the one that he quoted:
So, what we have is one paper that may have some flaws that says that their best estimate for climate sensitivity puts it in the lower part of the IPCC range…hardly a reason not to be concerned about the effects of increasing greenhouse gases. Rather, it means that we have a better hope of making the transition away from the dinosaur of fossil fuels in a way that is still soon enough to prevent the worst damage but still gradual enough to not have a very large economic impact…that is unless the “merchants of doubt” continue to delay things, making the eventual necessary transition more rapid (and starting from a higher baseline).
Prediction: AR5 will come out with continued terrible futures written all through it, Pachauri will say what a great job he has done and now he is retiring, and the in-coming guy will back down the CO2 alarm with reference to “new” data, especially “new” satellite and ARGO floats, thank the Lord and Patchy that the IPCC urged these studies to be done.
Meanwhile, in Australia, a female Prime Minister will retire to write a book on how she and her country stood up, alone, to do their duty to the world, though thank the Lord the troubles went away with China’s sulphur and soot emissions, despite the HFCs it is releasing.
Well! Don’t I feel vindicated. These numbers add weight to my little method of estimating climate forcing (I use a method from combustion engineering called the path length method). If Steve Mosher reads this, I’d appreciate a clarification of something. The MODTRAN is an estimate based on HIGHTRAN. Does MODTRAN go to very high levels of CO2? The estimate of absorbance from the combustion engineering method seems to track the climate estimates pretty well at levels up to about 100 bar.cm, but start to diverge after that. By 800 bar.cm the curves are distinctively different. The combustion engineering estimates indicate that the rise in absorbance would be nearlhy parallel to the x axis, even with a log/log plot. The climate model absorbance would be a straight line rising constantly in a log/log plot.
Speaking of feedbacks, I have had a nice back and forth with Dr. Schmidt at Realclimate. He was very polite and helpful, so I thought I’d give him a positive plug for that. I now have a rational explantion as to why the ocean is so cold. It is based on the ability of evaporation at high latitudes to pull large amounts of heat out of the ocean. When there is open ocean with windy air at cold temperatures (like -20 or colder), the rate of evaporation is pretty high, so the phase transfer portion of heat transfer dominates. This cooled water then sinks (salt water does not reach a density maximum at 4C like fresh does) I haven’t fully digested this yet, but this would appear to be a very significant negative feedback. Conductive transfer through ice would be much lower than evaporative transfer. That is, as it gets colder, more ice forms and heat loss decreases. Similarly, as it gets warmer, ice cover decreases and the area available for this heat transfer mechanism increases, hence heat loss increases. The heat loss at the polar area is important because atmospheric water is lower there and hence radiant loss from the atmosphere to space will be higher.
Konrad says:
You are talking nonsense here.
(1) In fact, treating water as a blackbody in the far infrared is an excellent approximation. It has an emissivity that differs from 1 by a very small amount (less than 1%, as I vaguely recall).
(2) Your idea that objects that evaporatively cool somehow behave different radiatively is without any merit that I know of. The amount a body radiates does not depend on the amount that it cools by other means. It just depends on its temperature, surface area, and emissivity.
I think you are all giving way too much credit to a paper which ,
a) is not published yet
b) is a whole bunch of computer models, with, as far as I can see, no new
experimental data at all
c) contains a lot of escape clauses listing all the features that have not yet been investigated
but which could affect the results
d) and ends with a statement that more research is needed…..
Remember this post by Willis?
http://wattsupwiththat.com/2011/09/26/allergies-and-dr-broecker/
The consensus folks were in high praise for how prescient this guy was in 1975 and tried to use the paper to flog skeptics.
Guess what senstitivity he used?
Arfur Bryant says:
That is a transient climate response, not an equilibrium climate sensitivity. And, 2.25 K happens to be very close to what the IPCC models give on average for the transient climate response (whereas their average equilibrium sensitivity is about 3.3 K).
Strange…You seem to use the word “variability” to mean “variability only in the direction that I want it to vary in”. Natural variability can occur in two directions, up and down. It could be that the temperatures would have been lower in the absence of anthropogenic forcings. Even if you think that this is unlikely, what we did know with a pretty high degree of certainty is that the net effect of anthropogenic aerosols is to cause cooling. There is still too much uncertainty to narrow down very well how much warming that greenhouse gases otherwise would have caused they may be offsetting, which is why the modern temperature record does not produce very strong constraints on estimates of the climate sensitivity.
So long as the greenhouse effect is retained, there is no climate science. Everyone and his brother has brought forth evidence that there is no consistent correlation of CO2 with temperature in the modern era, and my comparison of temperatures in the atmospheres of Venus and Earth makes it obvious that there is no greenhouse effect in either one (for CO2 concentrations from less than 0.033%–in 1976, when Earth’s “Standard Atmosphere” was last updated–up to 96.5% for Venus; in other words, for any concentration of CO2).
Just as a postscript on my last post, here is the table from the IPCC AR4 report that lists the equilibrium climate sensitivities and transient climate responses for the various models considered in the IPCC report: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch8s8-6-2-3.html#table-8-2
The ice ages were:
… not started by CO2, …
… nor sustained by CO2 levels, …
… nor influenced by CO2 levels, …
… (except that the CO2 levels reduced forest cover and increased grassland/tundra).
The 800 year lag which occurs very consistently throughout all of the timelines available in the ice ages should be considered enough evidence of the above by itself. Perhaps one need to think about that logically to understand it rather than be biased by a CO2-based climate theory.
Harry Dale Huffman says:
November 9, 2011 at 4:58 pm
So long as the greenhouse effect is retained, there is no climate science.
http://theendofthemystery.blogspot.com/2010/11/venus-no-greenhouse-effect.html
Harry’s work is worth a read. It is consistent with the findings in other studies, that surface temperature is determined by a gravity and solar energy. Everything else – water and co2 – they are simply going along for the ride.
This would explain why for zillions of years the earth’s average temperature has remained in a very narrow band from 285 – 295 K. That is about a 3% variance in average temperature over the past 600 million years.
The only explanation that is reasonable for such a small variation is that something that does not vary very much must regulate temperature. CO2 and H2O both vary too much to be the climate regulators.
The mean should be around 0.4°C, with a serious non-zero sub-zero tail. AGW is bunkum, stem to stern.
@Mike Jonas says:
>From IPCC Report AR5, July 2015, para 2.7.1 3: “There have been estimates of a lower climate sensitivity (Schmitter et al 2011, …) but there are some ambiguities and they remain controversial.”. There is no other reference to it in the report.
+++++
It has been perfectly legimitate to take all model outputs and average them with no concern as to how well they were performing when the numbers were generated. Someone will produce a paper that claims it is 8 degrees, so the average of all these views will be 4.
There. Solved.
Joel Shore says: and so on
Joel, I don’t know your educational or experience background, but you appear to be very conversant with all the pro-AGW literature. As for me, I’m just a degreed accountant with some statistical training, at least enough for auditing purposes. In my 60 years on this planet I’ve experienced some interesting and severe weather. In 24 years of military service, I’ve been in the arctic in the winter, and the desert and jungle in the summer. I’ve taught scuba diving and had mixed gas training. In other words, I’ve lived in the real world and accumulated some practical knowledge to go with my academic knowledge. We all know CO2 is an odorless, colorless trace gas required by green plants to produce the sugars and O2 that support life on this Earth. We also know that the concentration of CO2 in our atmosphere is nowhere near the level where living, breathing animals are in danger of suffocating. But you, and others like you, are expounding on an unproven idea that increasing CO2 levels are causing the planet to warm, and relying on computer models to bolster your argument. Without any real proof showing cause and effect. Instead of arguing over models and statistics based on questionable data, why not design some real experiments to prove the idea.
Paul Linsay says:
November 9, 2011 at 3:43 pm
At the top of the atmosphere where the CO2 radiates energy into outer space there is no such restriction. It’s all done by the strong spectral lines. This means that doubling the CO2 will double the rate at which IR will be radiated into space. I have no idea if the models take this into account, but I’d be real surprised, more like shocked, if they didn’t.
This cooling effect of CO2 is never separated from the warming effect as far as I’ve been able to tell. They attempt to cover both by building vertical profiles of the atmosphere. I think I read where they use 3 of these profiles and all the models are built off these estimates. It’s something like estimating global temperature by averaging 3 weather stations.
There was an even better assault on the IPCC’s sensitivity calculations in July. There was this thread on it on WUWT:
There were these threads on it elsewhere:
Paul Linsay says:
November 9, 2011 at 3:43 pm
“At the top of the atmosphere where the CO2 radiates energy into outer space there is no such restriction. It’s all done by the strong spectral lines. This means that doubling the CO2 will double the rate at which IR will be radiated into space. I have no idea if the models take this into account, but I’d be real surprised, more like shocked, if they didn’t.”
Richard M says:
November 9, 2011 at 7:30 pm
“This cooling effect of CO2 is never separated from the warming effect as far as I’ve been able to tell. ”
Very good points. I’d add that at the surface we have maximum temperatures limited by convection and not radiation, therefore the increased emissivity at the top of the troposphere dominates and the net effect of CO2 is cooling, meaning that the sensitivity is actually negative. At least, let’s begin to consider that possibility.
John Eggert says:
November 9, 2011 at 4:29 pm
==============================================
See below – temperature has little to do with evaporation but relative humidity does. In winter, we watch snow sublimate with wind and sun without any melting. Sea Ice forms at around minus 1.8 degrees C and there is a density difference – ice is water, and much less dense than sea water and the system is much more complex than your “model” presented from you discussion with Dr. Schmidt. Bing sea ice formation and spend a few hours reading. Only the top 100 to 150 metres of the northern oceans are involved in the cooling effect due to the existence of the pycnocline: http://www.arctic.noaa.gov/essay_wadhams.html (try not to laugh at the last sentence of the essay)
Note also that there is much more evaporation at the equator and increased salinity (34 ppm) versus the Bering sea for example (32 ppm) so I don’t follow your thoughts on heat loss from evaporation being larger in the northern oceans though it may be for other reasons – too complex for a short review but from all I can see, evaporation in the northern oceans is vary low so you need another hypthesis: http://www.eoearth.org/article/Arctic_Ocean
=================================================================
On evaporation:
Sunlight penetrates the water to heat it up very slightly and air temperatures can warm the water also, but these play smaller roles in evaporation of water than the amount of water vapor in the air above the water.
Evaporation from a water body with no internal heating (like a hot spring) is controlled by the water vapor content of the air above the water and by the amount of turbulence in the air that can take evaporated water vapor away from the water surface.
The less water vapor in the air, the more water can be evaporated from the lake, no matter what the temperature.
The more turbulence (usually increases with wind speed), the faster the evaporated water vapor is removed from the near the water surface, thereby increasing the rate of evaporation.
David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory
And if you really want to play with formulae: http://van.physics.illinois.edu/qa/listing.php?id=1440
http://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html
National Weather Service information –
http://www.grow.arizona.edu/Grow–GrowResources.php?ResourceId=208
I’m not certain what everyone is so excited about.
It is a model. It has lower sensitivity estimates than other models commonly cited by the IPCC. I don’t think the models that the IPCC cites have a lot of credibility, and I don’t see why this model should be seen as credible either. It provides a lower sensitivity estimate than the IPCC models, but even though I have reason to believe that the IPCC models are estimating too high, is there anything about THIS model that suggests we should see it as more credible than any other model?
When I see someone produce estimates that have some degree of verification from actual measurements, then I’ll get excited.
Until then, beware confirmation bias. We now live in a world in which warmists, many of whom believe warming will be a disaster, cheer every sign of a warming world as they think it proves them right. Skeptics, many of whom believe that a cooling world would be a disaster, cheer every sign of lower temperatures as a means to prove themselves right.
Are the cheerleaders for this paper cheering because they have reason to believe it is right? Or only because it suggests a number lower than what the warmists would have us believe?
It is inconceivable that paleo evidence can provide a better constraint on climate sensitivity than the 20th century temperature record. Think about it.
Lukewarmers. Nice
Robert Wood says:
November 9, 2011 at 8:56 pm
It is inconceivable that paleo evidence can provide a better constraint on climate sensitivity than the 20th century temperature record. Think about it.
#####
The 20th century record can only get you the TCR. paleo gets you the ECR.
so you have it backwards. the equillibrium climate response ( sensitivity) takes centuries to develop. 150 years of temperature data can only get you the transient response, not the steady state response.
John.
I could not tell you exactly what level of C02 that MODTRAN is validated to off the point of my head. best to start just reading some of the validation literature or better look at LBL stuff.
steven mosher says:
November 9, 2011 at 9:19 pm
…the equillibrium climate response ( sensitivity) takes centuries to develop…
And is complete hogwash for that very reason. The forcings are changing over that period also. How could you know that the climate sensitivity itself is not changing?