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Lower Climate Sensitivity Estimates: New Good News

“A collection of research results have been published in the peer-reviewed scientific literature in recent months that buoys my hopes for a low-end climate sensitivity.”

One of the key pieces to the anthropogenic climate/environment change puzzle is the magnitude of the earth’s climate sensitivity—generally defined as the global average temperature change resulting from a doubling of the atmospheric concentration of carbon dioxide (CO2).

One of the reasons that the “climate change” issue is so contentious is that our understanding of climate sensitivity is still rather incomplete. But new research efforts are beginning to provide evidence suggesting that the current estimates of the climate sensitivity should be better constrained and adjusted downwards. Such results help bolster the case being made by “lukewarmers”—that climate change from anthropogenic fossil-fuel use will be moderate rather than extreme, and that an adaptive response may be more effective than attempts at mitigation.

In its Fourth Assessment Report (AR4), released in 2007, the Intergovernmental Panel on Climate Change (IPCC) provided this general guidance on the climate sensitivity:

[The equilibrium climate sensitivity] is likely to be in the range 2°C to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement of models with observations is not as good for those values.

In IPCC parlance, “likely” means an expertly assessed likelihood of an outcome or result with greater than a 66% chance of occurrence. “Very unlikely” means less than a 10% change of occurrence.

Visually, the IPCC’s assessment of the climate sensitivity based on its interpretation of the extant literature at the time of its assessment is shown in Figure 1. The IPCC routinely includes studies which conclude that 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.


Fig 1. Climate sensitivity distributions retained (and in some cases recast) by the IPCC from their assessment of the literature. Note that the distributions fall off much more slowly towards the right, which indicates that the IPCC considers the possibilities of the climate sensitivity having a very large positive value (that is, a large degree of global temperature rise for a doubling of the atmospheric carbon dioxide concentration) to be not inconsequential (source: IPCC AR4).

If the true value of the climate sensitivity does turn out to exceed 6°C, then we will be in for what will probably turn out to be fairly disruptive climate change. Heck, even if the climate sensitivity lies much above 4.5°C, coming climate change will be substantial. I for one, would hope that it lies below 3°C, and actually turns out to be closer to 2°C.

A collection of research results have been published in the peer-reviewed scientific literature in recent months that buoys my hopes for a low-end climate sensitivity. Here are some salient quotes.

From “Climate Sensitivity Estimated from Temperature Reconstructions of the Last Glacial Maximum,” by Andreas Schmittner et al, 2011:

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.

From “Bayesian estimation of climate sensitivity based on a simple climate model fitted to observations of hemispheric temperatures and global ocean heat content,” by Magne Aldrin et al., 2012:

The [climate sensitivity] mean is 2.0°C… which is lower than the IPCC estimate from the IPCC Fourth Assessment Report (IPCC, 2007), but this estimate increases if an extra forcing component is added, see the following text. The 95% credible interval (CI) ranges from 1.1°C to 4.3°C, whereas the 90% CI ranges from 1.2°C to 3.5°C.

From “A climate sensitivity estimate using Bayesian fusion of instrumental observations and an Earth Systems model,” by Roman Olson et al., 2012:

Current climate model projections are uncertain. This uncertainty is partly driven by the uncertainty in key model parameters such as climate sensitivity (CS)…The mode of [our] climate sensitivity estimate is 2.8°C, with the corresponding 95% credible interval ranging from 1.8 to 4.9°C.

The above papers examined the “equilibrium climate sensitivity”—that is the global temperature change that results when all climate systems reach equilibrium with the changes in climate forcing that result from a doubling of the atmospheric carbon dioxide content. The time it take to reach equilibrium depends largely on the response of the oceans (and how quickly heat is distributed with in them) and is not known with much certainty. Estimates of the time to reach equilibrium run from decades to centuries. Thus, the equilibrium climate sensitivity may not be the best measure of how much temperature (and related) change may occur over the nearer term, like say, over the course of the remainder of the 21st century.

A better estimate of that change is the “transient climate response”, or the amount of global temperature change that is manifest at the actual time that the atmospheric carbon dioxide is doubled (rather than waiting for the system to reach complete equilibrium). The transient climate response (TCR) is somewhat less than the equilibrium climate sensitivity.

Two recent papers examined the transient climate sensitivity. Again, here are salient quotes.

From “Improved constraints on 21st-century warming derived using 160 years of temperature observations,” by Nathan Gillett et al., 2012:

Our analysis also leads to a relatively low and tightly-constrained estimate of Transient Climate Response of 1.3–1.8°C, and relatively low projections of 21st-century warming… which is towards the lower end of the observationally constrained range assessed by [the IPCC AR4].

From “Probabilistic estimated of transient climate sensitivity subject to uncertainty in forcing and natural variability,” by Lauren Padilla et al., 2011:

For uncertainty assumptions best supported by global surface temperature data up to the present time, this paper finds a most likely present-day estimate of the transient climate sensitivity to be 1.6 K, with 90% con?dence the response will fall between 1.3 and 2.6K…

Now, by no means am I suggesting either that 1) the quotes above reflect all the intricacies of the respective papers, or 2) that these results are end all and be all on the topic. Neither, in fact, is true.

But, the excerpts above do reflect the general conclusion of each paper, as well as what makes them noteworthy. In fact, the IPCC in its Fifth Assessment Report (which is now under construction) will be terribly remiss (and misleading) if they present a Figure that looks anything like Figure 1 (above) from their Fourth Assessment Report.

In the intervening years, there has been substantial research into the probability distribution which contains the earth’s equilibrium climate sensitivity and the emerging bulk of evidence suggests that the IPCC’s “likely” range for the equilibrium climate sensitivity is much too large and that the possibility that the equilibrium climate sensitivity lies above 6°C is vanishingly small—if not entirely ruled out. Even the chance that it exceeds 4.5°C has been markedly reduced to being no more than about 5% (if not even less).

And when it comes to the “best estimate” of the “most likely” value of both the equilibrium climate sensitivity as well as the transient climate response, it is refreshing and encouraging to see new results from different research groups pointing to a lower number than that forwarded by the IPCC in its AR4.

It seems as we obtain more knowledge and understanding of reality, the specter of alarming climate change is driven further into the world of make believe.

References:

Aldrin, M., et al., 2012. Bayesian estimation of climate sensitivity based on a simple climate model fitted to observations oh hemispheric temperature and global ocean heat content. Environmetrics, doi:10.1002/env.2140.

Gillett, N.P., et al., 2012. Improved constraints on 21st-century warming derived using 160 years of temperature observations. Geophysical Research Letters, 39, L01704, doi:10.1029/2011GL050226.

Olson, R., et al., 2012. A climate sensitivity estimate using Bayesian fusion of instrumental observations and an Earth System model. Journal of Geophysical Research, 117, D04101, doi:10.1029/2011JD016620.

Padilla, L. E., G. K. Vallis, and C. W. Rowley, 2011. Probabilistic estimates of transient climate sensitivity subject to uncertainty in forcing and natural variability. Journal of Climate, 24, 5521-5537, doi:10.1175/2011JCL13989.1.

Schmittner, A., et al., 2011. Climate sensitivity estimated from temperature reconstructions of the Last Glacial Maximum, Science, 344, 1385-1388, DOI: 10.1126/science.1203513.

21 comments

1 Eddie Devere { 03.19.12 at 9:41 am }

Thanks for the links to these research articles.
Let’s hope that the IPCC decides to promote science rather than fear.
I’m glad that researchers in the field are starting to develop better methods for predicting the ‘climate sensitivity.’ The methods in the papers you presented are a lot better than the estimates of ‘climate sensitivity’ based off of the CO2 & temperature data from ice core data. (This is the data that Al Gore used in his movie and book from Lonnie Thompson of The Ohio State University without Lonnie’s approval. The CO2 and temperature data seems to track each other well for 100,000′s of years. Of course, until the present, at which point CO2 has shot up dramatically and the temperature as only increased slightly. Here’s some of the data. http://eo.ucar.edu/staff/rrussell/climate/paleoclimate/ice_core_proxy_records.html
Of course, Al Gore fails to show the data on the ‘dust’ and fails to show recent data on CO2/temperature on the same scale. When you include the data for ‘dust’, you can see that the climate is highly sensitive to the amount of dust in the atmosphere. The climate is only weakly sensitive to CO2 in the atmosphere. The CO2 sensitive is most likely greater than 1 deg C/doubling, but as others are starting determine using satellite data, the CO2 sensitivity is likely only between 2-3 degC/doubling.)

The question is: are any of the people calling for CO2 taxes/caps willing to make predictions of future warming to test their hypothesis?

And then finally, once we have a good estimate for the ‘climate sensitivity’, (i.e. an estimate that correctly predicts future warming)
we need to incorporate the value of climate sensitivity into models that predict the economic and environmental impact of such a temperature rise.
There is no point fear-mongering until we have both the ‘climate sensitivity’ and the ‘economic/environmental impact as a function of increased temperature.’
Thanks for educating the public on this extremely ‘sensitive’ topic.

2 Lionell Griffith { 03.19.12 at 10:45 am }

I see. There is a simulated/estimated/reconstructed /computed/wag correlation between a temperature rise of ~2 +- 4 degrees K and a doubling of CO2 concentration. ALL of which are based upon the unsubstantiated assumption that increasing CO2 causes an increase in global temperature. Scientific malpractice alert!

What if something unexamined, unmeasured, and not thought of is causing the increase in temperature which in turn is causing the increase in CO2? This is an important question to answer because it is well known, but apparently forgotten, correlation does not and cannot show the direction of causality. All it can show is the extent to which the measurements of two measured parameters vary together. It says NOTHING about the underlying reality of either parameter.

A strong case can be made that the logical flaw behind all attempts to compute the so called “climate sensitivity” is that it is assumed that which must be proved. That is a logical and scientific no-no of the highest order. Prove the prior, demonstrate the hypothetical consequence, and then discuss rather than jump to unwarranted conclusions. Either that or simply stop your discussion at the point you have demonstrated a correlation and carefully point out that neither causality nor the direction of causality is not in any way implied by the study. In other words actually be honest rather than playing “let’s pretend”.

As near as I can tell, nearly everyone in the climate game are trying to game the system by omitting vital steps in the scientific process. They go by leaps and bounds from assumptions to conclusions without really doing the work necessary to prove their case. Chicken Little had more actual direct evidence that the sky was falling because something actually fell from above and hit her on the head than almost the entirety of the climate cult (Science? No. Actual science has been left on the cutting room floor. ).

3 David Appell { 03.19.12 at 11:30 pm }

Lionel, the scientific malpractice is on your part — the greenhouse properties of CO2 gas are very well-established and are the soundest part of climate science, because the standard, established methods of thermodynamics, statistical mechanics, spectroscopy, and quantum mechanics can be applied. It’s the feedbacks and other factors, such as aerosols and clouds, that cause the uncertainties.

No one is skipping any part of the scientific process — that’s a scurrilous charge for which you present absolutely no evidence.

And if you have a suggestion for an overlooked factor that is causing all the warming, by all means suggest it and investigate it. Maybe some unimagined factor causes apples to fall off trees, but so far the best theory is that masses attract gravitationally. Should I wait for this new factor to be discovered before I take precautions against falling?

4 rbradley { 03.19.12 at 11:45 pm }

David: Good to hear from you again.

Sufficiently high negative feedback effects would have to explain a lack of warming from the enhanced greenhouse effect, other things the same. Not saying it exists, however.

5 Chip Knappenberger: Lower Climate Sensitivity Estimates: New Good News | JunkScience.com { 03.20.12 at 5:46 am }

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6 Ray { 03.20.12 at 5:39 pm }

I’m still waiting for somebody to explain how the supposed global average temperature is calculated. Weather stations do not calculate average temperature. They record the extremes, high and low, but not average. Seventy percent of the earth is covered with water so no temperatures are available for most of the earth. How can you calculate the global average temperature when the local average temperature is unavailable?

7 Jean Demesure { 03.20.12 at 5:49 pm }

David Appell : “the greenhouse properties of CO2 gas are very well-established and are the soundest part of climate science, because the standard, established methods of thermodynamics, statistical mechanics, spectroscopy, and quantum mechanics can be applied.”

Yet, there is no agreement on CO2 sensitivity without feedback! And no credible explanation why there is no hotspot as predicted by models.
Calling that “very well-established and soundest part of climate science” is just more evidence that climate science is desperately poor. No amount of hand waving will save the day.

8 David Appell { 03.21.12 at 9:54 pm }

Ray { 03.20.12 at 5:39 pm } wrote:
> I’m still waiting for somebody to explain how the
> supposed global average temperature is calculated.

Why are you waiting instead of going out and finding the answer? The techniques have been explained in published papers by the groups doing the calculations, such as GISS. For example,

Hansen, J.E., and S. Lebedeff, 1987: Global trends of measured surface air temperature. J. Geophys. Res., 92, 13345-13372
http://pubs.giss.nasa.gov/cgi-bin/abstract.cgi?id=ha00700d

Jones, P.D., Lister, D.H., Osborn, T.J., Harpham, C., Salmon, M. and Morice, C.P., 2012: Hemispheric and large-scale land surface air temperature variations: an extensive revision and an update to 2010. Journal of Geophysical Research
http://www.agu.org/pubs/crossref/2012/2011JD017139.shtml

There are many more throughout the years.

9 David Appell { 03.21.12 at 10:07 pm }

Jean Demesure { 03.20.12 at 5:49 pm }
And no credible explanation why there is no hotspot as predicted by models.

There is no discrepancy between models and observations on this topic when the analysis is done correctly. People like Singer and Douglass have *not* done it correctly and are drawing bad conclusions, which people like you repeat. For details see:
http://davidappell.blogspot.com/2011/05/fred-singers-lecture-at-portland-state.html

10 David Appell { 03.21.12 at 10:12 pm }

Jean Demesure { 03.20.12 at 5:49 pm }
Calling that “very well-established and soundest part of climate science” is just more evidence that climate science is desperately poor. No amount of hand waving will save the day.

It’s not hand waving. Read something like Chapter 4 in Pierrehumbert’s textbook, covering work done going back to Guy Callendar in the 1930s, and you’ll see the immense amount of work that has gone into the physics of radiative transfer in the atmosphere. You can start here:
http://www.aip.org/history/climate/Radmath.htm

11 David Appell { 03.21.12 at 10:15 pm }

rbradley { 03.19.12 at 11:45 pm } wrote:
Sufficiently high negative feedback effects would have to explain a lack of warming from the enhanced greenhouse effect, other things the same.

What lack of warming? A decade of lower-than-long-term-average warming of the surface? That’s hardly unusual, and meanwhile the oceans — which are by far the best place to look for an energy imbalance, not a 2-dimensional surface — are warming strongly and consistently.

12 Brian H { 03.24.12 at 8:06 pm }

Notwithstanding Appell’s persistent nonsense, the fact that the IPCC et al have the #1 feedback with the wrong sign mean that the entire exercise is bollocks. Observed results of a doubling (which unfortunately is very unlikely) would be at most 10% of the stated ranges, and would have a tail projecting into negative numbers.

13 David Appell { 03.25.12 at 12:26 am }

Brian H, I presume you mean clouds, about which models very in sign — and no one is sure of the sign anyway, so you can’t know if the IPCC is wrong or not.

A doubling of CO2 is hardly unlikely, since we are still on the upslope of the Bell curve and haven’t even begun to notice indications of a top yet. CO2 levels are increasing about 0.5% per year, up from 0.4%/yr in 1975, and at this rate would double by about 2070. Seeing that corporations are pumping more oil and gas than ever, and seeing the sharp increases in Chinese and Indian use, a doubling looks very likely.

Your “at most 10%” claim has no scientific backing.

14 Weekly Climate and Energy News Roundup | Watts Up With That? { 03.25.12 at 6:34 pm }
15 Matt Ridley and the Wall Street Journal misrepresent paper cited in Ridley column | The Way Things Break { 12.22.12 at 12:15 pm }

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