Hot year prompts greenhouse concern.

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Planet Earth steamed straight into the 1990s with record-setting temperatures that extended the warming trend of the last two decades. In separate statements released last week, two groups of researchers reported that the global average surface temperature during 1990 was the highest in more than a century of weather measurements.

While most climate experts say they cannot tell whether the warming trend results from the buildup of greenhouse gases, some display an increasing willingness to draw suggestive connections.

Although it is still too early to confirm whether the recent exceptional warmth is related to the greenhouse effect, international scientific opinion strongly supports the reality of this enhanced greenhouse effect, and it is likely it has played some role in contributing to the recent warmth," asserts a group of British scientists who monitor global records of land and marine temperatures.

That's possibly stronger than what we've said in recent years," team member Phil Jones told SCIENCE NEWS.

Jones, of the University of East Anglia in Norwich, and his colleagues report that six of the seven warmest years in their 140-year-long record have occurred since 1980. And researchers who have analyzed land-station data at NASA's Goddard Institute for Space Studies in New York City say the seven warmest years on their century-plus record occurred since 1980. Both groups find a 0.5 degrees C warming over the last century

The scientists stress that the overall warming trend of the last decade holds much more significance than any single year's temperatures. Nonetheless, 1990 held a peculiarity that raised many eyebrows: its record warmth received no boost from a temporary tropical warming known as El Nino. The exceptionally high temperatures of several years in the 1980s resulted in part from such warmings, but there was no El Nino in 1990.

Measurements from balloons indicate that the troposphere - the lowest part of the atmosphere - has also warmed recently, says James K. Angell of the National Oceanic and Atmospheric Administration in Silver Spring, Md. In the 23-year record of tropospheric temperatures, 1988 and 1990 share first place.

Angell also reports that the lower stratosphere - the layer above the troposphere - has cooled dramatically over the last two decades, with 1990 registering the lowest temperatures. This pattern corresponds roughly with the greenhouse theory, which predicts that the upper atmosphere will cool as the lower atmosphere warms.

Angell says he has been skeptical of colleagues who connected the warming trend with the greenhouse effect. "But I must say, I'm beginning to waver. The succession of warm years in the 1980s is pretty impressive," he adds.

What does last year's warmth indicate about the future? Perhaps nothing. But NASA's James Hansen says the record temperatures in recent years match the predictions of computer climate models, lending credence to model forecasts of a major warming by the middle of the next century