UN report on global warming: much worse than originally thought

by H. Josef Herbert
Associated Press

WASHINGTON (AP) - 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 of 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."