Talk of "global cooling" based on bogus statistics

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There's an inevitable problem with trying to find trends in data that is subject to a great deal of random variability: unless the most recent point was a record high, it will always look like there's a downward trend. We're currently seeing that happen with the global temperature record, where the warmest year ever recorded, 1998, is receding into the past. As a result, reports of "global cooling" are appearing in the popular press, and smaller percentages of the US public are confident that the globe is warming. Unfortunately, all of this seems to be a misdirection; the Associated Press has performed a statistical sanity check on the claims of global cooling, and found that there's little to them.

As the AP report notes, the cries of global cooling have become increasingly obvious, with the phrase appearing on the cover of the new book Super Freakonnomics and the BBC asking "What happened to global warming?"

But, as we noted in February, the reent drop in temperatures has been so small that 2008 was still the 10th warmest on record. Other recent years were equally warm or warmer, while the hottest year on record, 1998, was unusually warm compared to the surrounding years. In fact, if you started tracking trends in either 1997 or 1999, you saw a general increase in global temperatures.

The AP went beyond this analysis by sending out temperature data to four statisticians, without informing them what the data represented, and asked them to identify any trends in the data. Apparently, none of them saw any sign of global cooling. All of them detected the upward trend that is apparent when periods longer than a decade are examined, while the ups-and-downs of the last decade appear similar to the statistical noise that occurs in other decades within the data set. One of the statisticians is even quoted as saying that seeing a downward trend in recent years involves "people coming at the data with preconceived notions."

Statistically valid or not, the high profile of the sites where claims of global cooling are being given credence appears to be weighing in with the public. Last week, the Pew Research Center released theresults of a poll of 1,500 US adults, who were asked about climate change. Over the past year, acceptance of the data showing that the Earth has warmed plunged, dropping from 71 percent of respondents to 57 percent. Far fewer accept the verdict of most scientists, namely that human influences are the primary driver of recent climate changes. Here, only 36 percent of the public agreed.

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