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Discrepancies in global warming data.

The Earth has warmed substantially over the last century. That's what scientists conclude when they look at several temperature records compiled by separate teams, all showing a similar degree of global warming. But a new analysis of the separate records reveals that the data do not agree in their details, raising questions about whether scientists can use these records to decipher the cause of the warming.

"All these records turn out to be different, which means that we cannot really rely on [them]," says Anastasios A. Tsonis of the University of Wisconsin-Milwaukee.

He and James B. Elsner of Florida State University in Tallahassee compared three records of average annual temperatures in the northern hemisphere, compiled over the past 97 years. Previous comparisons, using standard statistical techniques, showed a high degree of consistency among the records. But Tsonis and Elsner contend those techniques do not work well with such small data sets. Instead, they used a newer statistical technique called bootstrapping (SN: 7/27/91, p.56), which they call ideal for studying small data sets. From each of the temperature records, a computer generated 1,000 sets of simulated data. Tsonis and Elsner then compared the averages of those sets. In the July Geophysical Research Letters, they report that the bootstrap procedure uncovered significant discrepancies among the three records.

The long-term warming trend seen in each record is real, Tsonis says, but he now questions the veracity of the finer details - the shorter-term warmings or coolings in the records. Without such confidence, he says, it's impossible to tell whether the long-term warming results from a natural fluctuation in the climate or from the greenhouse gases accumulating in the atmosphere.

James Hansen, a climate expert at NASA's Goddard Institute for Space Studies in New York City, contends that the new findings merely point out that the records contain inherent uncertainties, a problem already recognized by researchers. Despite the uncertainties, he and other climatologists believe the records contain reliable information.

Tsonis and Elsner argue, however, that the records may not be as trustworthy as scientists think.
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Publication:Science News
Date:Aug 10, 1991
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