Tuesday, March 27, 2007

Climate Change

At National Review Online, Jim Manzi reviews and explains, for lay dummies like me, the tremendous scientific uncertainties underlying the global warming debate. Even I can understand the following:
When evaluating model reliability, the second test—can it predict accurately?—is the acid test. We can debate all day about whether a model is complete enough, but if it has correctly predicted major climate changes over and over again, that is pretty good evidence that its predictions should be taken seriously. There are plenty of studies that show what is called “hindcasting,” in which a model is built on the data for, say, 1900-1950, and is then used to “predict” the climate for 1950-1980. Unfortunately, it is notoriously common for simulation models in many fields to fit such holdout samples in historical data well, but then fail to predict the future accurately. So the crucial test is actual prediction, in which a model is run today to forecast the climate for some future time-period, and then is subsequently validated or falsified. No global climate model has ever demonstrated that it can reliably predict the climate over multiple years or decades—never.

At the Right Coast, Mike Rappaport comments, "My understanding of the debate is that all of this is uncontroversial. Why there should be a consensus in favor of the stronger predictions, not to mention the extremism of Al Gore, would seem to be a mystery."

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