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Experts cite 'strong evidence' of global warming


Panel finds spike in temperatures over last two decades

January 13, 2000
Web posted at: 11:41 a.m. EST (1641 GMT)

In this story:

Temperature has risen sharply

Differing temperatures don't disprove trend

'Blanket' wrapping Earth's surface


WASHINGTON (CNN) -- A blue-ribbon panel of climate scientists has issued a report saying that global warming is "undoubtedly real."

VideoCNN's Rick Lockridge explains the study.
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Global climate

The report, announced Wednesday night in a statement by the National Academy of Science's National Research Council, takes an unusually strong stand on the issue. It also undermines a principal argument used by scientists who dissent with the majority view, which is that global warming is well under way with possibly dire environmental consequences.

The panel stopped short of declaring a definite link between human activity and global warming.

Temperature has risen sharply

Global temperatures have risen more sharply in the past 20 years than at any time this century, according to the panel, led by John Wallace of the University of Washington.

The panel of scientists says that contradictory evidence from satellite data, used by some scientists and political activists to dismiss reports of a warming planet, is irrelevant.

NASA scientist John Christy, compiling satellite data extending back to 1979, has contended that temperature measurements in the Earth's upper atmosphere show a cooling of two degrees Fahrenheit over the past two decades.

Because most climate scientists have presumed that global warming would affect all layers of the atmosphere in a uniform way, Christy's research has been a cornerstone argument for those who disagree with reports on the severity or even the existence of global warming.

Differing temperatures don't disprove trend

But two years ago, Christy acknowledged math errors in his computations that reduced the cooling measurements to about one-half degree Fahrenheit.

Wednesday's report asserts that external factors, including the thinning layer of ozone in the Earth's upper atmosphere; the rapid rise in particulate pollution from the burning of fossil fuels; and natural impacts like the massive 1991 eruption of the Mount Pinatubo volcano in the Philippines make it possible for the upper atmosphere to cool while the Earth's surface is rising to record temperatures.

"The differences between the surface and upper-air trends in no way invalidates the conclusion that the Earth's temperature is rising," said Wallace, the panel's chair.

Christy is one of 11 scientists who participated in the panel that produced the new report.

The most comprehensive assessment to date of the possible impacts of global warming are contained in the 1995 report of the Intergovernmental Panel on Climate Change, or IPCC, a United Nations-sponsored effort of more than 2,500 climate scientists, including the panelists.

'Blanket' wrapping Earth's surface

The IPCC reached a near-unanimous conclusion that global warming was at least partially a result of human activity -- primarily the burning of fossil fuels, which release carbon dioxide, methane, and other gases into the atmosphere, forming a global "blanket" that traps heat near the Earth's surface.

The IPCC predicted an increase in global temperatures of between 2 and 6.3 degrees Fahrenheit by the year 2100. The panel also predicted the expansion of warming oceans, and the melting of land-based ice formations would combine to add between one and three feet to sea level.

The IPCC projected increases in the frequency and intensity of storms and droughts; spread of tropical diseases; sharp increases in coastal flooding; and an accelerated wave of extinctions of plant and animal species which fail to adapt to the changing climate.

Wednesday's panel also included Benjamin Santer, a principal author of the IPCC report; and James Hansen, whose dramatic 1988 testimony before the U.S. Congress triggered some of the first widespread reports of global warming.

The topic of global warming has spawned parallel debates in the scientific and the political communities.

China to lead U.S. in greenhouse emissions

A 1997 global conference in Kyoto, Japan resulted in a treaty that would commit industrialized nations to reductions in so-called greenhouse gas emissions; but the U.S. Senate has remained staunchly opposed to ratifying the treaty -- nullifying its impact in the nation that currently leads the world in Greenhouse emissions.

Critics of the treaty say the economies of industrialized nations would suffer under the Kyoto Accords, which would impose no such limits on developing nations at this time.

China, with a booming, coal-based economy, is projected to zoom past the United States in greenhouse emissions by 2025.

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