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Global Warming Debunked! (or Not...)

A few days ago, a bunch of conservative bloggers had themselves a little uproar. Noel Sheppard wrote, "[A] government agency is actually participating in a fraud against the American people." Fraud! The culprit, it seems, was James Hansen, head of NASA's Goddard Institute. "[L]eftist hero James Hansen is behind this deliberate fraud," wrote The Ace. "He should be frog-marched out of his office." A different blogger, Ace of Spades, agreed: "Fire him. Immediately." Rush Limbaugh called the whole affair "more evidence, ladies and gentlemen, that this whole global warming thing is a scientific hoax." And so on.

So, pray tell, what was the "fraud"? It seems that Steve McIntyre, a Canadian statistician and longtime global-warming skeptic, had discovered an error in NASA's surface temperature records for the United States. He sent off an email to NASA, and James Hansen fixed the problem, crediting McIntyre for the good catch. Right-wing blogs promptly went ballistic and said this shows that climate science is all a bunch of hokum.

But how big an error was it? Well, 1998 went from being listed as 0.01 degrees warmer than 1934 to being listed as 0.02 degrees cooler. That means 1934 is back to being the "official" hottest U.S. year on record, although it's still a statistical tie. Some of the other U.S. years in this decade were also downgraded slightly. This all had virtually no bearing on the global temperature record, in which 2005 still appears to be the hottest year on record, and Al Gore's claim that nine of the ten warmest years in history have occurred since 1995 is still operative. Check out RealClimate for some graphs.

Nothing's really changed. But there are a few things to note here. One, I'm not sure what the "fraud" is. Conservatives keep claiming that Hansen is being secretive about his "algorithms," although the methods for NASA's analysis are all laid out in painstaking detail here. Two, it's interesting that Hansen himself--the man who apparently needs to be "frog-marched out of his office"--doesn't seem to have ever claimed that 1998 was unequivocally the hottest U.S. year ever. Here's what he wrote in 2001 (which was prior to making the error that McIntyre found):

The U.S. annual (January-December) mean temperature is slightly warmer in 1934 than in 1998 in the GISS analysis. ... In comparing temperatures of years separated by 60 or 70 years the uncertainties in various adjustments (urban warming, station history adjustments, etc.) lead to an uncertainty of at least 0.1ºC. Thus it is not possible to declare a record U.S. temperature with confidence until a result is obtained that exceeds the temperature of 1934 by more than 0.1ºC.

The two years were, as he admitted, in a statistical tie back in 2001, and they're still in a tie today. Third, it's no secret whatsoever to climate scientists that the 1930s were a hot decade for the United States. They know about the Dust Bowl, etc. Really. Here's a paper laying out the differences between the warm weather of the '30s--which was largely confined to the high latitudes--and the more serious warming of today (see p. 5). Among other things, the Arctic ice wasn't disappearing as rapidly in the 1930s. Which is just to say that Mark Steyn's column on the subject is, as you'd expect, total nonsense.

Finally, some bloggers seemed to be confused and think that this error somehow debunks scientific climate projections. But the models used to predict future warming aren't constructed using surface temperature records--they're physical models, not statistical models. And there's plenty of other evidence for man-made global warming besides NASA's temperature series. But no matter, the right-wing blogosphere has moved on to complaining that the media isn't giving this "scandal" the coverage it deserves. Tim Lambert has all the comic details.

--Bradford Plumer