January 26, 1989

U.S. Data Since 1895 Fail To Show Warming Trend

By PHILIP SHABECOFF, Special to the New York Times

Correction Appended

After examining climate data extending back nearly 100 years, a team of Government scientists has concluded that there has been no significant change in average temperatures or rainfall in the United States over that entire period.

While the nation’s weather in individual years or even for periods of years has been hotter or cooler and drier or wetter than in other periods, the new study shows that over the last century there has been no trend in one direction or another.

The study, made by scientists for the National Oceanic and Atmospheric Administration was published in the current issue of Geophysical Research Letters. It is based on temperature and precipitation readings taken at weather stations around the country from 1895 to 1987.

Dr. Kirby Hanson, the meteorologist who led the study, said in a telephone interview that the findings concerning the United States do not necessarily ”cast doubt” on previous findings of a worldwide trend toward warmer temperatures, nor do they have a bearing one way or another on the theory that a buildup of pollutants is acting like a greenhouse and causing global warming. He said that the United States occupies only a small percentage of Earth’s surface and that the new findings may be the result of regional variations.

Readings taken by other scientists have suggested a significant warming worldwide over the last 100 years. Dr. James E. Hansen, director of National Aeronautic and Space Administration’s Institute for Space Studies in Manhattan, has reported that average global temperatures have risen by nearly 1 degree Fahrenheit in this century and that the average temperatures in the 1980’s are the highest on record.

Dr. Hansen and other scientists have said that that there is a high degree of probability that this warming trend is associated with the atmospheric buildup of carbon dioxide and other industrial gases that absorb and retain radiation.

But other scientists, while agreeing with this basic theory of a greenhouse effect, say there is no convincing evidence that a pollution-induced warming has already begun.

Dr. Michael E. Schlesinger, an atmospheric scientist at Oregon State University who studies climate models, said there is no inconsistency between the data presented by the NOAA team and the greenhouse theory. But he said he regarded the new data as inconsistent with assumptions that such an effect is already detectable. More Droughts Predicted

Many of the computer models that predict global warming also predict that certain areas, including the Midwest in the United States, would suffer more frequent droughts.

Dr. Hanson of NOAA said today that the new study does not in any way contradict the findings reported by the NASA scientists and others. He said that his study, in which he was joined by George A. Maul and Thomas A. Karl, also of NOAA, looked at only the 48 contiguous states.

Dr. Hanson said that global warming caused by the greenhouse effect might have been countered by some cooling phenomenon that has not yet been identified and that the readings in his study recorded the net effect.

”We have to be careful about interpreting things like this,” he said. What About Urbanization? One aspect of the study that Dr. Hanson said was interesting was the finding that the urbanization of the United States has apparently not had a statistically significant effect on average temperature readings. A number of scientists have theorized that the replacement of forests and pastures by asphalt streets and concrete buildings, which retain heat, is an important cause of rising temperatures.

Dr. Hansen of NASA said today that he had ”no quarrel” with the findings in the new study. He noted that the United States covered only 1.5 percent of Earth. ”If you have only one degree warming on a global average, how much do you get at random” when taking measurements in such a relatively small area, he asked rhetorically.

”We are just arguing now about whether the global warming effect is large enough to see,” he added. ”It is not suprising we are not seeing it in a region that covers only 1.5 percent of the globe.”

Dr. Hansen said there were several ways to look at the temperature readings for the United States, including as a ”statistical fluke.”

Possibililty of Countereffects

Another possibility, he said, was that there were special conditions in the United States that would tend to offset a warming trend. For example, industrial activity produces dust and other solid particles that help form liquid droplets in the atmosphere. These droplets reflect radiation away from Earth and thus have a cooling influence.

Dr. Hansen suggested that at some point there could be a jump in temperature readings in the United States if the measurements in the new study were a statistical aberration or the result of atmospheric pollutants reflecting heat away from Earth. He noted that anti-pollution efforts are reducing the amount of these particles and thus reducing the reflection of heat.

Several computer models have projected that the greenhouse effect would cause average global temperatures to rise between 3 and 8 degrees Fahrenheit in the next century. But scientists concede that reactions set off by the warming trend itself could upset these predictions and produce unanticipated changes in climate patterns.

Legislative Action Sought

Coincidentally with the new report, legislation was introduced in the Senate today prescribing actions for addressing the threat of global warming. Senator Al Gore, Democrat of Tennessee, introduced a bill that calls for creating a Council on World Environmental Policy to replace the White House’s Council on Environmental Quality. This change would emphasize the international aspects of environmental issues.

The bill would also require a ban on industrial chemicals that not only are depleting the atmosphere’s ozone layer, which blocks harmful ultraviolet radiation, but are believed to be contributing to the warming trend. It would also require stricter fuel-economy standards for automobiles to reduce the consumption of gasoline to reduce carbon dioxide.