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Global Climate Will Not Increase Dramatically, Study Indicates

January 15, 2002-- Some global warming scenarios envision temperatures rising over the next 100 years to the point that plants will produce less and seas will rise dramatically, swamping coastal cities.

Other scenarios suggest only slight global temperature increases with coastal zones remaining high and dry and plant production actually increasing.

Which is right?

The less dramatic one, the one that "looks more like the same world as today," is right, says Virginia State Climatologist Patrick Michaels. He has published a paper in the current issue of the journal Climate Research that calls into question the high end of the temperature ranges projected by the United Nations’ Intergovernmental Panel on Climate Change (IPCC), of which Michaels is a member.

"The rate of warming will not be much different than it was over the last 30 years," said Michaels, a professor of environmental sciences at the University of Virginia.

While most climate models produce a constant rate of future warming, that rate varies dramatically. Michaels’ research was designed to determine which of these rates are more likely than others.

Michaels uses nature itself as his model, comparing past real temperature rates to those predicted in computer models.

“Nature has been integrating the response to greenhouse effect changes for nearly a half-century, while models have been producing diverse projections,” Michaels notes.

Two years ago the IPCC produced its third assessment report, which indicated a global rise in temperatures of 1.4 to 5.8 degrees Celsius for 1990 to 2100.

Michaels' new independent study indicates the most likely value is around 1.6 degrees Celsius, near the low end of the IPCC range He used an assortment of data to produce a range of possible temperatures for the period, and all were substantially less broad than the IPCC’s range.

In one scenario, he used data from recent studies that closely examine the assumptions made about climate behavior in the U.N. report and found a range of warming of 1.1 to 2.8 degrees Celsius.

When using data of actual climate change rates during the past 25 years of greenhouse warming, and projecting it out to the year 2100, he found a range of 1.5 to 2.6 degrees Celsius.

“Almost all models produce a constant rate of warming,” Michaels said. "So why not let nature choose that rate?”

When he factored both aspects of his study together, he found a range of 1.0-1.6 degrees Celsius.

Additionally, by adjusting the averages of a range of climate models to reflect actual observed changes in temperature in nature, he found a warming range of 1.3-3.0 degrees Celsius, with a central value of 1.9 degrees Celsius.

"The consistency of these somewhat independent results encourages us to conclude that 21st century warming will be modest and near the low end of the IPCC's third assessment report projections," he said.

Michaels says that much of the data in the panel's report is based on older, less accurate studies that take into account neither what has actually occurred in nature during the past century nor the more refined and accurate independent findings of more recent studies.

"Our paper looks at what should have been examined in the IPCC report," he said. "We should be listening to nature talking."

Michaels also said society is producing more fuel-efficient machinery and will continue to do so throughout this century, further reducing the likelihood of dramatic warming.

"This is why we shouldn't rush policy decisions before we have strong and clear evidence that our projections are sound," Michaels said. "In this study we demonstrate that the IPCC's evidence for intense warming projections is weak, but the evidence for the low end of their range is very strong”.

The full article can be accessed at:

Contact: Fariss Samarrai, (434) 924-3778

FOR ADDITIONAL INFORMATION: Contact the Office of University Relations at (434) 924-7116. Television reporters should contact the TV News Office at (434) 924-7550.

SOURCE: U.Va. News Services


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