How Hot Was It in the 20th Century?

The New York Times did a nice report on the recent blogosphere brouhaha over the what was or was not the hottest year in U.S. To wit:

A quarter-degree Fahrenheit is roughly the downward adjustment NASA scientists made earlier this month in their annual estimates of the average temperature in the contiguous 48 states since 2000. They corrected the numbers after an error in meshing two sets of temperature data was discovered by Stephen McIntyre, a blogger and retired business executive in Toronto. Smaller adjustments were made to some readings for some preceding years.

All of this would most likely have passed unremarkably if Mr. McIntyre had not blogged that the adjustments changed the rankings of warmest years for the contiguous states since 1895, when record-keeping began.

Suddenly, 1934 appeared to vault ahead of 1998 as the warmest year on record (by a statistically meaningless 0.036 degrees Fahrenheit). In NASA's most recent data set, 1934 had followed 1998 by a statistically meaningless 0.018 degrees.

Never mind that the statistical meaninglessness of such minor temperature fluctuations was not much stressed in the past by NASA's climate guru James Hansen. According to the Times Hansen now says:

Dr. Hansen and his team note that they rarely, if ever, discuss individual years, particularly regional findings like those for the United States (the lower 48 are only 2 percent of the planet's surface). "In general I think that we want to avoid going into more and more detail about ranking of individual years," he said in an e-mail message. "As far as I remember, we have always discouraged that as being somewhat nonsensical."

"Discouraged as being somewhat nonsensical?" Really? Then what about this February 2007 NASA press release which quotes Hansen as saying:

"2007 is likely to be warmer than 2006," said James Hansen, director of NASA GISS, "and it may turn out to be the warmest year in the period of instrumental measurements. Increased warmth is likely this year because an El Nino is underway in the tropical Pacific Ocean and because of continuing increases in human-made greenhouse gases."

The NASA release very helpfully lists the five warmest years as, 2005, 1998, 2002, 2003 and 2006. But Hansen might object, "I was talking about global temperatures not U.S. temperatures." OK, fine. But the release does seem to be discussing "individual years."

Self-confessed climate change denier, Stephen Brett, makes the same point over at the Wall Street Journal today:

But just how "meaningless" would this have seemed had it yielded the opposite result? Had Mr. McIntyre found that a collation error understated recent temperatures by 0.15 degrees Celsius (instead of overstating it by that amount, as he discovered), would the news coverage have differed in tone and approach? When it was reported in January that 2006 was one of the hottest years on record, NASA's James Hansen used the occasion to warn grimly that "2007 is likely to be warmer than 2006." Yet now he says, in connection to the data revision, that "in general I think we want to avoid going into more and more detail about ranking of individual years."

Brett also points to the distressing fact some leading climate change proponents refuse to share their data:

I confess: I am prepared to acknowledge that the world has been and will be getting warmer thanks in some part to an increase in man-made atmospheric concentrations of greenhouse gases. I acknowledge this in the same way I'm confident that the equatorial radius of Saturn is about 60,000 kilometers: not because I've measured it myself, but out of a deep reserve of faith in the methods of the scientific community, above all its reputation for transparency and open-mindedness.

But that faith is tested when leading climate scientists won't share the data they use to estimate temperatures past and present and thus construct all-important trend lines. This was true of climatologist Michael Mann, who refused to disclose the algorithm behind his massively influential "hockey stick" graph, which purported to demonstrate a sharp uptick in global temperatures over the past century. (The accuracy of the graph was seriously discredited by Mr. McIntyre and his colleague Ross McKitrick.) This was true also of Phil Jones of the Climatic Research Unit at the University of East Anglia, who reportedly turned down one request for information with the remark, "Why should I make the data available to you, when your aim is to try and find something wrong with it?"

Science works by checking each by each. In fact, the error in the satellite temperature data was discovered because the principle investigator, University of Alabama Huntsville climatologist John Christy shared his data with climate change proponents. Surely data produced by climate change proponents could benefit from review by more skeptical scientists. Witness what just happened with NASA's U.S. temperature data.

Whole WSJ climate denier op/ed here.

Those of you for whom the climate change debate is of more than passing interest might want to check out McIntyre's Climate Audit and climate change proponents' RealClimate websites from time to time.