Statisticians reject global 'cooling' idea

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(China Daily)
Updated: 2009-10-28 10:16

WASHINGTON: An analysis of global temperatures by independent statisticians shows the Earth is still warming and not cooling as some global warming skeptics are claiming.

Statisticians reject global 'cooling' idea

The analysis was conducted at the request of The Associated Press to investigate the legitimacy of talk of a cooling trend that has been spreading on the Internet, fueled by some news reports, a new book and temperatures that have been cooler in a few recent years.

In short, it is not true, according to the statisticians who contributed to the analysis.

The statisticians, reviewing two sets of temperature data, found no trend of falling temperatures over time.

US government data show the decade that ends in December will be the warmest in 130 years of record-keeping, and 2005 was the hottest year recorded.

The case that the Earth might be cooling partly stems from recent weather. Last year was cooler than previous years. It has been a while since the superhot years of 1998 and 2005. So is this a longer climate trend or just weather's normal ups and downs?

In a blind test, the AP gave temperature data to four independent statisticians and asked them to look for trends, without telling them what the numbers represented. The experts found no true temperature declines over time.

"If you look at the data and sort of cherry-pick a microtrend within a bigger trend, that technique is particularly suspect," said John Grego, a professor of statistics at the University of South Carolina.

Yet the idea that things are cooling has been repeated in opinion columns, a BBC news story posted on the Drudge Report and in a new book by the authors of the best-seller Freakonomics. Last week, a poll by the Pew Research Center found that only 57 percent of Americans now believe there is strong scientific evidence for global warming, down from 77 percent in 2006.

Skeptics focus on 1998

Global warming skeptics base their claims on an unusually hot year in 1998. Since then, they say, temperatures have dropped - thus, a cooling trend. But it is not that simple.

Since 1998, temperatures have dipped, soared, fallen again and are now rising once more. Records kept by the British meteorological office and satellite data used by climate skeptics still show 1998 as the hottest year. However, data from the National Oceanic and Atmospheric Administration and NASA show 2005 has topped 1998. Published peer-reviewed scientific research generally cites temperatures measured by ground sensors, which are from NOAA, NASA and the British, more than the satellite data.

Statisticians reject global 'cooling' idea

The recent Internet chatter about cooling led NOAA's climate data center to re-examine its temperature data. It found no cooling trend.

"The last 10 years are the warmest 10-year period of the modern record," said NOAA climate monitoring chief Deke Arndt. "Even if you analyze the trend during that 10 years, the trend is actually positive, which means warming."

The AP sent expert statisticians NOAA's year-to-year ground temperature changes over 130 years and the 30 years of satellite-measured temperatures preferred by skeptics and gathered by scientists at the University of Alabama in Huntsville.

Statisticians who analyzed the data found a distinct decades-long upward trend in the numbers, but could not find a significant drop in the past 10 years in either data set. The ups and downs during the last decade repeat random variability in data as far back as 1880.

One prominent skeptic said that to find the cooling trend, the 30 years of satellite temperatures must be used. The satellite data tends to be cooler than the ground data. Key to that is making sure that 1998 is part of the trend, he added.

"I don't argue with you that the 10-year average for the past 10 years is higher than the previous 10 years," said Don Easterbrook, a Western Washington University geology professor and global warming skeptic, who has self-published some of his research. "We started the cooling trend after 1998. You're going to get a different line depending on which year you choose.

"Should not the actual temperature be higher now than it was in 1998?" Easterbrook asked. "We can play the numbers games."

That's the problem, some of the statisticians said.

Grego produced three charts to show how choosing a starting date can alter perceptions. Using the skeptics' satellite data beginning in 1998, there is a "mild downward trend," he said. But doing that is "deceptive."

The trend disappears if the analysis is begun in 1997. And it trends upward if you begin in 1999, he said.

"To talk about global cooling at the end of the hottest decade the planet has experienced in many thousands of years is ridiculous," said Ken Caldeira, a climate scientist at the Carnegie Institution at Stanford University.