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 Florida State University, at Tallahassee; coeducational; chartered 1851, opened 1857. Present name was adopted in 1947. Special research facilities include those in nuclear science and oceanography. 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 Bootstrapping A procedure used to calculate the zero coupon yield curve from market figures. Notes: Since the T-bills offered by the government are not available for every time period, the bootstrapping method is used to fill in the missing figures in order to derive the (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 Geophysical Research Letters is a publication of the American Geophysical Union. GRL is the organization's only letters journal. Since its introduction in 1974, GRL has published only short research letters, typically 3-5 pages long, which focus on a specific discipline or , they report that the bootstrap See boot. (operating system, compiler) bootstrap - To load and initialise the operating system on a computer. Normally abbreviated to "boot". From the curious expression "to pull oneself up by one's bootstraps", one of the legendary feats of Baron von Munchhausen. 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 veracity (v  ras´itē),n 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 The NASA Goddard Institute for Space Studies (GISS), at Columbia University in New York City, is a component laboratory of NASA's Goddard Space Flight Center Earth-Sun Exploration Division and a unit of The Earth Institute at Columbia University. in New York City New York City: see New York, city. New York City City (pop., 2000: 8,008,278), southeastern New York, at the mouth of the Hudson River. The largest city in the U.S. , 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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