There are three completely separate questions: (a) Has the global mean temperature recently increased? (b) Have human activities contributed to changes in cli

There are three completely separate questions: (a) Has the global mean temperature recently increased? (b) Have human activities contributed to changes in climate? (c) What are the likely effects (positive and negative) of a rise in global mean temperatures? Only nutball cranks think (a) is false. This is our strawman: if you reject "climate change," you must be a crank. In addition, much debate centers on (b)—if climate change is "our fault," it should be up to us to fix it. But (b) is irrelevant except insofar as it affects our options if the answer to (c) turns out to be "We are facing a global catastrophe." If astronomers discovered an asteroid on collision course with Earth, no one would be persuaded to inaction by the argument that "the asteroid isn't our fault." If you examine the political incentives producing the answers to (c), it's obvious that in the current climate (heh) negative consequences are favored over positive ones. In other words, an ambitious young climate scientist seeking to maximize her chances of tenure would be foolhardy to undertake a detailed investigation of the likely benefits of global warming. What we're seeing in climate science is, I think, a close parallel of what happened in Russian biology under the Soviets—specifically, the work of Stalin's favorite biologist, Trofim Lysenko. Lysenko developed a theory of the heritability of acquired characteristics (complete with fabricated laboratory experiments), which had obvious adaptive value in a régime seeking to develop, via social engineering, the "new Soviet man." Similarly, predicting global catastrophe is adaptive in a régime where government-funded science must be solving Important Problems™, and where most members of the permanent government believe the majority of proposed anti–global warming measures (alternative energy, conservation, carbon taxes, etc.) are good ideas anyway. So, do we really face global catastrophe as the result of climate change (human-induced or otherwise)? In an environment of Lysenkoist climate science, it's hard to say for sure. But you'll notice that the heritability of acquired characteristics didn't exactly pan out. And given that most climate simulations are currently "off model" [1]—i.e., their predictions don't match reality—we can reasonably guess the safe way to bet. [1]: http://esr.ibiblio.org/?p=5747 http://esr.ibiblio.org/?p=5747