Despite Research, ‘Greenhouse Effect’ Is Tough to Prove : Global Warming: Most scientists are convinced it’s happening but their belief seems to be based more on intuition and general knowledge than on facts.

A recent international survey shows that three-fourths of the scientists involved in climate-change research believe that global temperatures already are rising in response to civilization’s intensification of nature’s “greenhouse effect.”

But in spite of massive research efforts now under way, the conclusion that global warming is a reality seems to be heavily based on intuition and general knowledge of climate rather than specific research on the subject.

Fewer than half of the respondents (41%) said they believe scientific evidence now in hand supports the conclusion that accelerated warming of the atmosphere is taking place. And 71% said they believe temperature increases over the last century are within the range of normal climatic fluctuation.

The survey, to be published next week, was carried out by Global Change Environmental Report, an Arlington, Mass., newsletter that mailed questionnaires to 1,500 climate change scientists around the world. More than 330 scientists in 41 countries responded.

The results indicated that the world scientific community is subject to some of the same disagreements that for months have divided environmentalists and policy-makers. But there was little dispute over the validity of the much-discussed phenomenon itself.

Of those surveyed, 96% said they believe the basic greenhouse effect thesis--that increasing concentrations of carbon dioxide, methane, water vapor and other trace gases will cause the earth’s atmosphere to trap more of the sun’s heat and raise world temperatures.

Nearly two-thirds (65%) said they believe the odds are better than 50-50 that global temperatures will rise by three degrees over the next century.

While that is at the lower range of projections now accepted by the United Nations-sanctioned Intergovernmental Panel on Climate Change, 89% said they consider the threat serious enough to warrant immediate steps to limit carbon dioxide emissions.

Brady Hurley, the newsletter editor, said the survey was designed to elicit scientific opinion rather than to assess firm conclusions that can be drawn on the basis of existing evidence.

For government officials, the global warming debate for the last year has focused increasingly on the issue of reducing carbon dioxide emissions from fossil fuel combustions.

Several European governments, led by the Netherlands, have adopted plans for stabilization of carbon dioxide emissions, followed by outright reduction. The Bush Administration has refrained from endorsing such proposals, maintaining that it needs more information on the science of climate change and the economic impact of carbon dioxide reduction.

At a White House-sponsored conference last month, the Administration found itself at odds with European officials who were more interested in discussing plans for action than for additional research.

The conference was followed by an international gathering of parliamentarians, who urged governments to take steps to combat climate warming, although scientists studying computer models still are unable to forecast the regional consequences of increased temperatures.

Of the scientists responding to the newsletter survey, 71% said they believe a global temperature rise of a few degrees would cause “major detrimental impacts for humanity.”

Of those, 91% said they would expect changes in rainfall patterns sufficient to shift world food production, 88% foresaw a rise in sea levels, and 66% predicted an increase in the severity of tropical storms.