Scientists cautious on why world warming up

Press, 12 April 1988, Page 14

Scientists cautious on why world warming up

By GLENNDA CHUI NZPA San Jose, 11 California Last year was | the world’s warmest year on record, capping J the warmest decade in a century, three groups of scientists have independently concluded. Although the balmy weather fits predictions of the greenhouse effect, the long-feared warming of the climate, the [ researchers stop short of blaming that phenomenon for the temperature increase. I | ;

“The circumstantial case, in my opinion, is damn strong,” i said Stephen Schneider, of the National Centre for Atmospheric Research in Boulder Colorado.

“The greenhouse effect is our best explanation, but the other culprits that could have done it ... have not been accounted for.”

Climate experts say a global warming could change rainfall patterns, melt glaciers and , flood coastal cities. i

“The key question for society is not whether the change will take place, but the rate,” Schneider said. “If it dribbles in, we can adapt If it' roars in, we get hurt.”

I The ! world’s temperature, said to average about*, 15 deg., differs only a fiction from year to xroov* hut cinrri th#a turn nf

the century, it has risen a fraction of a degree, according to two of the studies. Although that doesn’t sound like much, small ’ temperature changes can have drastic effects. Two of the three studies say 1987 was the warmest year on record. In the third report, it tied for first place with 1981. In any case, “the 1980 s are the warmest decade in the history of instrumental records,” said James Hansen, director of N.A.S.A.’s Goddard Institute for Space Studies in New York,, who directed one study.

“The four wannest years in the record were all in the 1980 s.” However, he said it would be years before scientists could tell whether the warming trend was related to the greenhouse effect or simply a statistical fluke. The greenhouse theory, first described in the 1800 s, predicts that gases given off by the burning of fossil fuels — coal, petrol and oil — will warm up the earth’s climate. The gases, primarily carbon dioxide, act like greenhouse windows by letting sunlight on to the earth’s surface, but not letting heat escape.

The three studies are “certainly compatible with what the modeK are nrpdirtino ’’ caid Alan

Hecht, director !of the National Climate Programme Office, and editor of the “Journal of Climate.”

“We just don’t know enough about the natural system to jump quickly, but it’s something we’re going to be monitoring more every year?’;

The studies, wliich have not yet been published in the scientific literature, are based on temperature measurements . taken over wide areas of the globe. A group at the University of East Anglia, in England, analysed temperature records from about 1750 locations around the world dating back to the 1880 s, when the first reliable measurements were made.

A study financed by the United States: Department of Energy found I that 1987 was the warmest year yet. If the warming trend continues, “by ;the year 2000, for certain, people would not be i able to deny” the greenhouse effect was at work, said a climatologist, [ ! Philip Jones, who worked on the study. Hansen and a~col!eague, analysing similar records for about 10001 locations, found the average surface temperature had gone up a I fraction of a I degree in the last century.! By their reckoning, 1987> tied with 1981 as the warmest year on record. closelv

followed by 1983 aqd 1980. | ' In a third study, James Angell, of the: National Oceanic and Atmospheric? Administration, 1 has kept track of temperatures dt 63 spots around*the world, sending up balloons to check them at heights up to 24km. i •! From 1958 ; to 1987, there was a small, barely significant warming at the surface and in the lower atmosphere, Angell said. However, * the upper layers of the atmosphere had cooled | significantly. Such cooling is predicted by the greenhouse effect, because greenhouse gases would give off heat into space, cooling I the upper atmosphere? I / Scientists familiar with , the three studies said they / appeared to be based on solid observations, but they cautioned that climate was influenced by many things, i from the periodic warming of the oceans known:as El Nino to volcanic eruptions, and these influences were poorly understood. “It may be that a lot of the signal was driven by natural phenomena related to El Nino," Hecnf“ said. . 1 | . !j “I think we need multiple evidence! to confirm the temperature readings.” ■ • ; | Mjchael i MacCracken, an scientist at lawrence Livermore

National Laboratory, said temperature was just one symptom of the greenhouse i effect. Scientists also were looking for evidence that mountain glaciers were melting, sea level was rising or sea ice was changing response to warmer weather. Unfortunately, they didfhi not know exactly what look for because com-1 puter models' of the greenhouse effect do not agree. ;■ ■ | . Compounding 1 the problem, MacCracken said, “there simply haven’t been high-quality (temperature) measurements made all over the globe for example, in oceans in the southern hemisphere for am extended period.” Still, the recent studies ! added to a growing body 1 of evidence that something was wrong, said Rafe Pomerance, a senior associate at the World Resources Institute in Washington.! .'! ! : "Most important, these results are not contradictory to the predictions,” he said. “And, in fact, the most important thing we know is that the .warming gases iin the atmosphere continue to rise at'rapid and completely unacceptable rates.” . ; “It’s possible,” he added, “that we may look back on the 1980 s as the decade in which the J.. greenhouse signal • emereed.” I ' j | >