SPRING PULLS A FAST ONE; SCIENTISTS FIND SHORTER WINTERS AS EARTH WARMS.

Byline: William K. Stevens The New York Times

Separate studies using different methods in the past three years have found that as Earth's atmosphere warms, spring is arriving earlier and autumn is coming later in the Northern Hemisphere.

While much of the evidence has been indirect in the past, a direct examination of the actual behavior of plants across Europe appears to confirm the earlier findings.

The result, a number of scientists say, is a greener planet.

The new evidence comes from a network of 77 research sites called the International Phenological Gardens. Spread across the length and breadth of Europe, from northern Scandinavia to Greece and from Spain and Ireland to Poland andlgaria, the gardens contain genetically identical clones of various species of trees and shrubs.

Each spring from 1959 to 1993, observers at the sites recorded the dates when buds first appeared, leaves unfolded and plants flowered. Each fall, the observers noted the dates when leaves turned color and fell from trees.

Analyzing the resulting mass of data, two researchers at the University of Munich in Germany have found that over the three decades, the advent of spring has advanced an average of six days, while autumn was delayed an average of about five days.

This 11-day lengthening of the growing season was caused by warmer temperatures, concluded the researchers, Annette Menzel, a specialist in the study of forests, and Peter Fabian, who specializes in climate, meteorology and forests. Their report appears in the current issue of Nature.

Other recent studies have shown that buds are bursting open earlier in the spring in Canada, and studies in Britain have found that birds are lg their eggs earlier in the year.

In 1996, Charles D. Keeling of the Scripps Institution of Oceanography in San Diego reported that an earlier spring in the Northern Hemisphere was reflected in the seasonal rise and fall of atmospheric carbon dioxide levels. Plants ``breathe'' carbon dioxide.

When plants drop their leaves in the fall and go dormant, atmospheric levels of the gas increase. When they regain the leaves in the spring, levels drop.

Analysis of these fluctuations revealed that spring was arriving across the hemisphere about a week earlier in the 1990s than in the 1970s.

In 1997, this finding was bolstered by a study by Ranga B. Myneni of Boston University and four other researchers, including Keeling. Using a different method, they found that spring was arriving about a week earlier in the early 1990s than in the early 1980s.

This study was confined to regions north of the 45th parallel, which runs through or near Yellowstone National Park, Minneapolis, Ottawa, Bo, Bordeaux, Belgrade and Vladivostok. North of that line, warming in recent decades has been substantially greater than the global average.

The Myneni study also found that fall was arriving later, with the result that the growing season in the northern climes had increased by 12 days, give or take four days. The researchers reached this conclusion by analyzing changes in solar radiation absorbed by plants as they perform photosynthesis. From this, the scientists were able to infer the arrival of the seasons.

Taken together, Myneni said, all the recent studies indicate that a warming and greening of the planet is indeed under way, and that the growing season should lengthen further if temperatures continue to rise.

Since the late 19th century, the average surface temperature of Earth has risen by about 1 degree Fahrenheit or a little more, with northern latitudes warming more than the global average. Most climate experts believe that emissions of heat-trapping waste industrial gases like on dioxide, a product of the burning of fossil fuels like coal and oil, are responsible for at least some of this warming.

This dominant view also holds that if emissions of the heat-trapping gases continue at the present rate, the average global temperature will rise by an additional 2 to 6 degrees, with a best estimate of 3.5 degrees, over the next century. This compares with a warming of 5 to 9 degrees since the depths of the last ice age some 20,000 years ago.

The predicted warming, the experts say, would disrupt Earth's climate, make both droughts and floods worse, cause the oceans to rise and push temperate-zone climatic zones farther north. It also would be expected to have some positive effects, not least the lengthening of growing seasons in northern latitudes.

According to the Menzel-Fabian study, the longer growing seasons already have arrived. The area of the study spanned almost the entire width of the northern temperate zone, from the sub-Arctic to the Mediterranean region. esearch; weather; winter; statistic; change; study; international phenological gardens