WASHINGTON - New evidence shows man-made pollution has ''contributed substantially'' to global warming and the earth is likely to get a lot hotter than previously predicted, a United Nations-sponsored panel of hundreds of scientists finds.
The conclusions by the Intergovernmental Panel on Climate Change, the most authoritative scientific voice on the issue, is expected to widely influence climate debate over the next decade.
The report's summary, a copy of which was obtained by The Associated Press, was being distributed to government officials worldwide this week.
It is the first full-scale review and update of the state of climate science since 1995 when the same panel concluded there is ''a discernible human influence'' on the earth's climate because of the so-called ''greenhouse'' effect caused by the buildup of heat-trapping chemicals in the atmosphere.
Today, the panel says in its new assessment that ''there is stronger evidence'' yet on the human influence on climate and that it is likely that manmade greenhouse gases already ''have contributed substantially to the observed warming over the last 50 years.''
And the scientists, in revised estimates, conclude that if greenhouse emissions are not curtailed the earth's average surface temperatures could be expected to increase from 2.7 to nearly 11 degrees Fahrenheit by the end of this century, substantially more than estimated in its report five years ago.
It attributes the increase - from a range 1.8 to 6.3 degrees Fahrenheit warmer in the 1995 assessment - mainly to a reduced influence now expected to be played by sulfate releases from industry and power plants. Such releases, which tend to have a cooling influence, will likely dramatically decline in industrial countries because of other environmental concerns, the scientists maintain.
''What this report is clearly saying is that global warming is a real problem and it is with us and we are gong to have to take this into account in our future planning,'' said Kevin Trenberth, head of climate analysis section at the National Center for Atmospheric Research.
''It definitely reinforces what we were able to say in 1995,'' added Tom Wigley, a climate scientist at the center in Boulder, Colo. ''It shows the previous projects (in 1990 and 1995) were conservative.''
Wigley, who did not participate in crafting the latest findings, was a key author of the 1995 report's section about the human impact on climate.
Others were less certain.
Michael Schlesinger, a climatologist at the University of Illinois at Champaign-Urbana, said despite the new information there is still insufficient knowledge about natural climate variables such as solar radiation that could change the assessment.
Comparing studies of climate to listening to noise radio transmissions, Schlesinger said in an interview:
''Science has moved closer to the radio transmitter, so the signal is higher and more apparent against the background noise. But the background noise has not diminished. There are still uncertainties and there may be very large surprises ahead.''
The IPCC's third assessment report is expected to get final approval at a United Nations conference early next year. While some wording will certainly be changed by government policy-makers, the central scientific conclusions may not be altered, several scientists who have been involved in the process said Wednesday.
Michael Oppenheimer, an atmospheric physicist at Environmental Defense, said the latest assessment ''reinforces the mainstream scientific consensus'' about global warming. Its new estimates of warming poses ''a risk of devastating consequences within this century.''
Three years ago industrial nations tentatively agreed to curtail the release of greenhouse gases - mainly carbon dioxide from burning fossil fuels - to below 1990 levels as a first step to address global warming.
But none of the major industrial countries has yet ratified the agreement, crafted in Kyoto, Japan in 1997. Skeptics argue that the science has yet to be conclusive and that computer models used to predict future climate is not reliable enough to warrant a dramatic, and possibly very expensive, shift in energy use to curtail carbon emissions into the atmosphere.
The issue also has crept into the presidential campaign. Vice President Al Gore has argued the science is clear and steps need to be taken soon to begin reducing greenhouse emissions. His Republican rival, Gov. George W. Bush, has not dismissed global warming, but urges a cautious approach and believes the science still needs to be proven.
The IPCC panel's summary of a voluminous technical report covering 14 chapters attempts to provide the most current state of scientific understanding of the climate system and potential for future warming.
While there are still uncertainties, the IPCC scientists say that there is an ''increasing body of observations'' that provide a ''collective picture of a warming world'' that cannot be solely explained by natural forces.
''Emissions of greenhouse gases and aerosols due to human activities continue to alter the atmosphere in ways that affect the climate system,'' the report says.
Various findings of the last five years have reinforced the IPPC's 1995 determination that climate change warrants top-level attention by government policy makers.
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