A few days ago, Nobel-winning chemist Paul Crutzen told Reuters, "It's a cruel thing to say, but if we are looking at a slowdown in the economy, there will be less fossil fuels burning, so for the climate it could be an advantage."
Except that, as The Washington Post's Andrew Freeman points out today in an excellent post, the actual "advantage" here will be pretty tiny, and hardly worth the economic pain. During the recessions in 1991 and 2001, it's true that U.S. emissions shrunk slightly, 0.7 percent and 1.6 percent, respectively. But small cuts like that aren't nearly enough—think of it this way, even if the entire world had zero emissions growth from now until eternity, and stayed at 2008 levels, carbon would still accumulate in the atmosphere, and we'd be in for some extremely unpleasant climate change as carbon concentrations in the air shot past 450 parts per million, then 550 ppm, then various feedback loops would start kicking in... (The newest fear is that peatlands will start drying out, belching up even more methane and carbon into the air as they do.)
And the thing is, we're not even seeing zero percent emissions growth. Between 2006 and 2007, even as the global economy started to slow down, greenhouse gas emissions rose 3 percent—largely due to developing countries like China. At this rate global temps may rise about 6 degrees C by the end of the century—apocalyptic territory. The rough consensus among climatologists is that we should reduce global greenhouse emissions 50 percent below 1990 levels by mid-century if we want to prevent runaway warming. Even a severe depression wouldn't come close to achieving that; all it would really do is scuttle investment in clean energy. (See Steve Mufson's piece in the Post today, describing how oil's return to $70/barrel, caused in part by the slowdown, has led to waning interest in plug-in hybrids, electric cars, and other fancy oil substitutes that were all the rage over the summer.)