Wednesday, August 19, 2009

Are the Predictions of Climate Models Credible? 

The lively debate in the comments on my post yesterday about the summer snowstorm in Wyoming included this assertion:
I'm sure there have been numerous studies on the soundness of climate models. I'm not familiar with all of them. What one finds though is that models are consistently improving and there is high confidence in the ranges given for future scenarios. There is broader range and greater realism. Studies show models have been able to reproduce past and current climate (see here). Chapter 8 of the IPCC's physical basis in the Fourth Assessment Report deals with climate models and their evaluation.
Well, here's the abstract of a peer-reviewed study in the International Journal of Climatology that disagrees with the commenter:
We examine tropospheric temperature trends of 67 runs from 22 �Climate of the 20th Century� model simulations and try to reconcile them with the best available updated observations (in the tropics during the satellite era). Model results and observed temperature trends are in disagreement in most of the tropical troposphere, being separated by more than twice the uncertainty of the model mean. In layers near 5 km, the modelled trend is 100 to 300% higher than observed, and, above 8 km, modelled and observed trends have opposite signs. These conclusions contrast strongly with those of recent publications based on essentially the same data.
The paper ends with this conclusion:
The last 25 years constitute a period of more complete and accurate observations and more realistic modelling efforts. Yet the models are seen to disagree with the observations. We suggest, therefore, that projections of future climate based on these models be viewed with much caution.
Reminder: You can hear Dr. Fred Singer, one of the authors of the paper above, at this afternoon's event sponsored by the Minnesota Free Market Institute.

Labels: ,