Scientists cool outlook on global warming

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Global warming may not be as dramatic as some scientists have predicted.

Using temperature readings from the past 100 years, 1,000 computer simulations and the evidence left in ancient tree rings, Duke University scientists announced yesterday that "the magnitude of future global warming will likely fall well short of current highest predictions."

Supported by the National Oceanic and Atmospheric Administration, the Department of Energy and the National Science Foundation, the Duke researchers noted that some observational studies predicted that the Earth's temperature could rise as much as 16 degrees in this century because of an increase in carbon dioxide or other so-called greenhouse gases.

The Duke estimates show the chances that the planet's temperature will rise even by 11 degrees is only 5 percent, which falls in line with previous, less-alarming predictions that meteorologists made almost three decades ago.

In recent years, much academic research has indicated otherwise, often in colorful terms and citing the United States as the biggest contributor to global warming. This month, a University of Toronto scientist predicted that a quarter of the planet's plants and animals would be extinct by 2050 because of rising temperatures. On Wednesday, two geophysics professors at the University of Chicago warned those who eat red meat that their increased flatulence contributes to greenhouse gases.

Last year, Oregon State University research linked future "societal disruptions" with global warming, while the Carnegie Institution reported that the insulating influence of northern forests alone would raise the Earth's temperature by 6 degrees. In 2004, Harvard University scientists informed Congress that warming had doomed the planet to climatic "shocks and surprises."

The Duke research, however, found substantial ups and downs in the Earth's temperature before modern times, countering other studies that confine noticeable temperature increases to the industrialized era. Marked climate change in other centuries resulted from "external forcing," said the Duke findings, citing volcanic eruptions and other influences.

"Our reconstruction supports a lot of variability in the past," said research director Gabriele Hegerl of Duke's Nicholas School of the Environment and Earth Sciences.

Although her study found that the Earth is, indeed, warming, Ms. Hegerl discounts dire predictions of skyrocketing temperatures. The probability that the climate's "sensitivity" to greenhouse-gas levels would result in drastically higher temperatures is "substantially" reduced, she said.

Ms. Hegerl and her four-member team based their conclusions on thermometer readings over the past century, along with "ancient climate records," including tree-ring studies and ice-core samples that revealed hot and cold spells and airborne particulates over a 700-year period. In addition, they created 1,000 computer-based weather simulations for the past 1,000 years.

"Ancient and modern evidence suggest limits to future global warming," the study concluded. It was published in the journal Nature.

The topic of global warming, meanwhile, will be framed dramatically in "An Inconvenient Truth," a 94-minute documentary featuring former Vice President Al Gore, who has deemed rising temperatures "a planetary emergency." The Hollywood production will be released to theaters in May and is billed by producer Davis Guggenheim as "the most terrifying film you will ever see."

The production also recommends that viewers take "political action." On Tuesday, Mr. Gore paid Roy Neel, a longtime Democratic adviser, $40,000 to help him create a public outreach program on global warming, the New York Daily News reported.

The American Spectator and columnist Jonah Goldberg have accused Mr. Gore of "green" scaremongering.