In response to all the lovely e-mails (and to preempt the inevitable George Will column): Yes, I've noticed it's bitterly cold across much of North America right now. Record lows, heavy snowfall, the works. Sadly, this doesn't prove global warming is fake. Long-term temperature trends do allow for short-term variation. A warming planet will still experience plenty of record lows. Via Joe Romm, here's a nice graph highlighting this point, from the National Center for Atmospheric Research:

Even though the 2000s were the hottest decade on record, there were a lot of record lows set in the United States during that time. It's just that there were even more record highs—and the ratio of highs to lows was greater than the ratio during the 1990s, which was, in turn, greater than the ratio during the 1980s, and so on. Note also that the United States is just a small patch of the globe, and while we're bracing ourselves against freakish cold, the central Pacific has been seeing freakish highs. The thing to watch is the overall trend.

And on that note, it's odd to see sites like Drudge hype all the recent news stories about record U.S. lows. A big reason we know that we're experiencing record colds is because of historical temperature data. The same data that skeptics keep claiming is flawed or forged. The same data showing a clear upward trend in average temperatures over the past 100 years. All of the sudden, that data's become mysteriously reliable...

P.S. On a more substantive note, here's an explanation for why much of the Northern Hemisphere has been so cold lately. Blame the Arctic Oscillation, which has taken an unusually wild lurch this winter.