Climate change measure for the common folk.

Siberians and Alaskans may be shedding their fur coats noticeably earlier this spring, according to a new measure of climate change.

To find out when global warming would be readily perceived by people, researchers at NASA's Goddard Institute for Space Studies in New York have created what they call a commonsense climate index. Using records of temperature and precipitation, they found that, since 1951, climate in most parts of the world has not shifted enough to be noticeable. However, in parts of Asia and northwestern North America, "climate change might already be apparent to longtime residents," say James Hansen and his colleagues in the April 14 Proceedings of the National Academy of Sciences.

"What this is focusing on is what people will feel--how many hot days there are, how many days of rain there are," comments Michael C. MacCracken of the U.S. Global Change Research Program in Washington, D.C.

The researchers chose to analyze temperature and precipitation because these climate variables affect people, crops, and the environment, says study coauthor James Hansen. The challenge, he says, was to distinguish normal climatic variation from long-term trends stemming from global warming (SN: 5/24/97, p. 316; 3/15/97, p. 156). Scientists measure global warming by assessing Earth's overall change in temperature, but compared to normal seasonal changes, those fractions of degrees Celsius don't seem like much.

Reasoning that many of today's adults grew up between 1951 and 1980, the team selected that interval as a baseline. The researchers hypothesize that to strike most people as noteworthy, weather patterns must have occurred, on average, only once every 6 or 7 years during the baseline period. Such a year was given a climate index of 1 or -1, depending on whether it was especially hot or especially cold.

The researchers combined several different annual measures of temperature and moisture into the climate index. For temperature, they used seasonal averages, the number of degree days for both the heating and cooling seasons, and the frequency of extremely hot or cold days. For moisture, the team included seasonal precipitation totals, the frequency of heavy precipitation, and a measure of drought stress on plants.

"I see this becoming more useful as time goes on. We're going to put this on the Web," Hansen says. "When you get an unusual year--unusually warm, unusually cold--you can look at [the index]" to see how the weather compares to the long-term trends.