As you may have heard, there has been no net warming of the planet since 2001, and no subsequent year was a warm as 1998 (admittedly a year with a major El Nino). A recent study by Keenlyside et al. (2008)  concludes that “global surface temperature may not increase over the next decade” due to natural oscillations in the Atlantic and Pacific Oceans.
As Patrick Michaels of the Cato Institute explained  at a recent congressional hearing, the suite of 21 climate models used in the IPCC’s mid-range emissions scenario (A1B) are on the verge of failing to reproduce actual climate data.
During the past 5 to 20 years, the observed trend in the average global temperature has been so low that it is starting to push the lower bounds of the climate models’ range of temperature predictions for that period. If 2009 is as cool as 2008 (with a La Nina brewing in the Pacific Ocean, that is not unlikely), then even the least sensitive of these models will be overestimating the actual amount of warming. And if Keenlyside is correct, and another decade elapses without significant warming, the models will have clearly failed.
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The most important point for policymakers and citizens, as Michaels notes, is that if the models predict too much warming, then all model-based assessments of global warming impacts on agriculture, human health, extreme weather, etc. will be similarly overestimated.
So what do you do if you’re a climate alarmist and the world isn’t warming up as much as you said it would? Why, you redefine “climate sensitivity.” You claim that agriculture, health, weather, etc. are more “sensitive” to increases in global temperature than scientists once believed. You say that less warming than the IPCC warned us about will lead to worse impacts than the IPCC warned us about. That’s the gist of a recent IPCC-sponsored study, as summarized here  by AP/MSNBC.com.