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A Fundamental Failure of Current Climate Models
Reference
Chase, T.N., Pielke Sr., R.A., Herman, B. and Zeng, X.  2004.  Likelihood of rapidly increasing surface temperatures unaccompanied by strong warming in the free troposphere.  Climate Research 25: 185-190.

Background
The authors note that "an important test of model predictive ability and usefulness for impact studies is how well models simulate the observed vertical temperature structure of the troposphere under anthropogenically-induced-change scenarios."  Why is this so?  It is because one of the most fundamental features of current climate-model simulations is "a larger warming in the free troposphere than at the surface when forced by increasing atmospheric greenhouse-gas concentrations and the direct effect of sulfate aerosols (IPCC 1996, 2001)."  If this predicted feature of global warming is not evident in the real world, there is little reason to believe anything else the models predict, including both the cause and (or) magnitude of the observed surface warming.

What was done
Chase et al. assessed the likelihood "that such a disparity between model projection and observations could be generated by forcing uncertainties or chance model fluctuations, by comparing all possible 22 yr temperature trends [for the years 1979-2000, which were similarly studied by the IPCC and a special committee of the U.S. National Academy of Science] in a series of climate simulations."

What was learned
In the words of the authors, "at no time, in any model realization, forced or unforced, did any model simulate the presently observed situation of a large and highly significant surface warming accompanied with no warming whatsoever aloft," which observations are openly acknowledged to represent the real world in both the IPCC (2001) report and the National Academy Report (2000).

What it means
Chase et al. conclude that these "significant errors in the simulations of globally averaged tropospheric temperature structure indicate likely errors in tropospheric water-vapor content and therefore total greenhouse-gas forcing, precipitable water and convectively forced large-scale circulations," noting that "such errors argue for extreme caution in applying simulation results to future climate-change assessment activities and to attribution studies (e.g. Zwiers and Zhang, 2003) and call into question the predictive ability of recent generation model simulations."

References
IPCC.  1996.  Second Assessment Report: Climate Change 1995. The Science of Climate Change.  Houghton,J.T., Meira Filho, L.G., Callender, B.A., Harris, N., Kattenberg, A. and Maskell, K. (Eds.).  Cambridge University Press, Cambridge, UK.

IPCC.  2001.  Third Assessment Report: Climate Change 2001. The Scientific Basis.  Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J. and Xiaosu, D. (Eds.).  Cambridge University Press, Cambridge, UK.

National Academy Report.  2000.  Reconciling Observations of Global Temperature Change.  National Academy Press, Washington, DC, USA.

Zwiers, F.W. and Zhang, X.  2003.  Towards regional-scale climate change detection.  Journal of Climate 16: 793-797.


Reviewed 3 March 2004