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Trouble in Climate-Model Paradise
Volume 10, Number 33: 15 August 2007

In an intriguing Climate Change report in Science, Wentz et al. (2007) note that the Coupled Model Intercomparison Project, as well as various climate modeling analyses, predict an increase in precipitation on the order of 1 to 3% per C of surface global warming. Hence, they decided to see what has happened in the real world in this regard over the last 19 years (1987-2006) of supposedly unprecedented global warming, when data from the Global Historical Climatology Network and satellite measurements of the lower troposphere have indicated a global temperature rise on the order of 0.20C per decade.

Using satellite observations obtained from the Special Sensor Microwave Imager (SSM/I), the four Remote Sensing Systems scientists derived precipitation trends for the world's oceans over this period; and using data obtained from the Global Precipitation Climatology Project that were acquired from both satellite and rain gauge measurements, they derived precipitation trends for the earth's continents. Appropriately combining the results of these two endeavors, they then derived a real-world increase in precipitation on the order of 7% per C of surface global warming, which is somewhere between 2.3 and 7 times larger than what is predicted by state-of-the-art climate models.

How was this horrendous discrepancy to be resolved?

Based on theoretical considerations, Wentz et al. concluded that the only way to bring the two results into harmony with each other was for there to have been a 19-year decline in global wind speeds. But when looking at the past 19 years of SSM/I wind retrievals, they found just the opposite, i.e., an increase in global wind speeds. In quantitative terms, in fact, the two results were about as opposite as they could possibly be, as they report that "when averaged over the tropics from 30S to 30N, the winds increased by 0.04 m s-1 (0.6%) decade-1, and over all oceans the increase was 0.08 m s-1 (1.0%) decade-1," while global coupled ocean-atmosphere models or GCMs, in their words, "predict that the 1987-to-2006 warming should have been accompanied by a decrease in winds on the order of 0.8% decade-1."

In discussing these embarrassing results, Wentz et al. correctly state that "the reason for the discrepancy between the observational data and the GCMs is not clear." They also rightly state that this dramatic difference between the real world of nature and the virtual world of climate modeling "has enormous impact," concluding that the questions raised by the discrepancy "are far from being settled." We agree. And until these "enormous impact questions" are settled, we wonder how anyone could conceivably think of acting upon the global energy policy prescriptions of the likes of Al Gore and James Hansen, who speak and write as if there was little more to do in the realm of climate-change prediction than a bit of fine-tuning.

Sherwood, Keith and Craig Idso

Wentz, F.J., Ricciardulli, L., Hilburn, K. and Mears, C. 2007. How much more rain will global warming bring? Science 317: 233-235.