Current Wisdom: Even More Low Climate Sensitivity Estimates

The Current Wisdom is a series of monthly articles in which Patrick J. Michaels, director of the Center for the Study of Science, reviews interesting items on global warming in the scientific literature that may not have received the media attention that they deserved, or have been misinterpreted in the popular press.

Our periodic compilations of low equilibrium climate sensitivity (ECS) estimates have become a big hit.

In our on-going effort to keep up with the science, today we update our previous summary with two additional recently published lower-than-IPCC climate sensitivity estimates—one made by Troy Masters and another by Alexander Otto and colleagues (including several co-authors not typically associated with global warming in moderation, or “lukewarming”).  There is also a third paper currently in the peer-review process.

The new additions yield a total of at least 16 experiments published in the peer-reviewed scientific literature beginning in 2011 that have found that the most likely value of the ECS to be well below the (previously?) “mainstream” estimate from the U.N.’s Intergovernmental Panel on Climate Change (IPCC). Since the negative impacts from global warming/climate change scale with the magnitude of the temperature rise, lower projections of future warming should lead to lower projections of future damages. We say “should” because one way around this, as the federal government has figured out, is to ignore all the new science indicating less expected future warming when calculating future damages, and inexplicably doubling the damages estimated to be caused by a given increment of carbon dioxide (a.k.a., social cost of carbon).

Here is a quick summary of the two new papers:

Examining the output of climate models run under increases in human emissions of greenhouse gas and aerosols, Troy Masters noted a robust relationship between the modeled rate of heat uptake in the global oceans and the modeled climate sensitivity. With this relationship in hand, he then turned to the observations to determine what the observed rate of oceanic heat uptake has been during the past 50 years or so. From the observed behavior, he was able to determine the climate sensitivity, and found it to be substantially less than that in the vast majority of the climate models. He found that the most likely value of the ECS from the observations was 1.98°C with a 90 percent range extending from 1.2°C to 5.15°C. He notes that the high end is driven by uncertainties in the oceanic heat uptake data earlier in the record.

Otto and colleagues used a simple energy budget model to relate observed global temperature changes to changes in the radiation climatology and the heat uptake in the earth system as humans have heaped various substances into the atmosphere. They conclude that the at best estimate for ECS is 2.0°C with a 90 percent range from 1.2°C to 3.9°C.

Both studies come with a long list of caveats relating to data quality, etc., that are common to all studies trying to estimate the ECS.

[Note: As mentioned, the third paper, which uses a similar methodology, is currently making its way through the peer-review process. The paper, authored by Ragnhild Skeie and colleagues finds the equilibrium climate sensitivity to be 1.8°C with a 90 percent range extending from 0.9°C to 3.2°C. If and when this paper is accepted, we’ll be sure to add the results to our chart. The paper is going through an open peer-review process, so you can follow its progress here.]

We’ve included these new results into our chart below (near the top just beneath the IPCC estimates; Otto et al. in red, Masters in dark purple).

 

Climate sensitivity estimates from new research beginning in 2011 (colored, compared with the range given in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) (gray) and the IPCC Fifth Assessment Report (AR5; black), which  has yet to be published. The arrows indicate the 5 to 95 percent confidence bounds for each estimate along with the best estimate (median of each probability density function; or the mean of multiple estimates; colored vertical line). Ring et al. (2012) present four estimates of the climate sensitivity and the red box encompasses those estimates. The right-hand side of the IPCC AR4 range is dotted to indicate that the IPCC does not actually state the value for the upper 95 percent confidence bound of their estimate and the left-hand arrow only extends to the 10 percent lower bound as the 5 percent lower bound is not given. The light grey vertical bar is the mean of the 16 estimates from the new findings. The mean climate sensitivity (3.4°C) of the climate models used in the IPCC AR5 is 13 percent greater than the IPCC’s “best estimate” of 3.0°C and 70 percent greater than the mean of recent estimates (2.0°C).

The average value of the best estimate of the equilibrium climate sensitivity across all the new studies is about 2.0°C. The average climate sensitivity of the climate models used by the IPCC to project future climate changes (and their impacts) is about 3.4°C—some 70 percent higher than the recent studies indicate.

As we have discussed, these new studies (which grow in number every couple of months) spell serious trouble for the IPCC and everyone else who shirks the responsibility of their own independent analysis and defers to the IPCC climate change projections instead (that finger would be pointing at you, EPA).

How long national and international organizations created to promote (i.e., the IPCC) or actually develop regulations (i.e., the EPA) can ignore the groundswell of new science, and instead continue with their charade that climate change is proceeding according to plan will surely be tested in the months to come. If this test does not come in the court of public opinion, in part from the growing community of scientists who recognize the disconnect between IPCC and the science, then it will almost certainly come from a court of law, where the challenges to the EPA’s callous indifference to new science and the regulations which have been and are being built upon it will certainly take place.

References:

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

Annan, J.D., and J.C Hargreaves, 2011. On the genera­tion and interpretation of probabilistic estimates of climate sensitivity. Climatic Change, 104, 324-436.

Hargreaves, J.C., et al., 2012. Can the Last Glacial Maximum constrain climate sensitivity? Geophysical Research Letters, 39, L24702, doi: 10.1029/2012GL053872

Intergovernmental Panel on Climate Change, 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Solomon, S., et al. (eds). Cambridge University Press, Cambridge, 996pp.

Lewis, N. 2013. An objective Bayesian, improved approach for applying optimal fingerprint techniques to estimate climate sensitivity. Journal of Climate, doi: 10.1175/JCLI-D-12-00473.1.

Lindzen, R.S., and Y-S. Choi, 2011. On the observational determination of climate sensitivity and its implica­tions. Asia-Pacific Journal of Atmospheric Science, 47, 377-390.

Masters, T., 2013. Observational estmates of climate sensitivity from changes in the rate of ocean heat uptake and comparison to CMIP5  models. Climate Dynamics, doi:101007/s00382-013-1770-4

Otto, A., F. E. L. Otto, O. Boucher, J. Church, G. Hegerl, P. M. Forster, N. P. Gillett, J. Gregory, G. C. Johnson, R. Knutti, N. Lewis, U. Lohmann, J. Marotzke, G. Myhre, D. Shindell, B. Stevens, and M. R. Alen, 2013. Energy budget constraints on climate response. Nature Geoscience, 6, 415-416,

Ring, M.J., et al., 2012. Causes of the global warming observed since the 19th century. Atmospheric and Climate Sciences, 2, 401-415, doi: 10.4236/acs.2012.24035.

Schmittner,  A., et al. 2011. Climate sensitivity estimat­ed from temperature reconstructions of the Last Glacial Maximum. Science, 334, 1385-1388, doi: 10.1126/science.1203513.

Skeie, R.B., T. Bernstsen, M. Aldrin, M. Holden, and G. Myhre, 2013. A lower and more constrained estimate of climate sensitivity using updated observations and detailed radiative forcing time series. Earth System Dynamics, in review.

van Hateren, J.H., 2012. A fractal climate response function can simulate global average temperature trends of the modern era and the past millennium. Climate Dynamics,  doi: 10.1007/s00382-012-1375-3.