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Thursday, October 19, 2006

Global Warming: Is It Real?

By Robert Roy Britt
Saturday, March 05, 2005

Senior Science Writer
posted: 07:15 pm ET
14 January 2000

In an effort to achieve consensus in one of the most contentious debates in modern science, a panel of 11 climate experts from diverse fields released a report Thursday stating that global warming is in fact a real phenomenon, at least near the surface of the planet.

After debating the issue in roundtable fashion for nine months, the panelists reported a very narrow slice of the debate, choosing to skirt the hot topic of whether or not human activity is contributing to global warming.

Still, the ambition of the report is broad, attempting to put to rest the question of whether or not surface temperatures are rising.

Finding consensus

The panel included university researchers, scientists from NASA and National Oceanic and Atmospheric Administration (NOAA), as well as experts in climate modeling, satellite data interpretation and sea-surface temperature analysis.

The group concluded that satellite data, though frequently debated, shows that the lower and middle troposphere -- a region extending from the Earth's surface to about 5 miles up -- has warmed only a little, if at all, in the past two decades.

The Earth's surface temperature, meanwhile, has risen between 0.7 and 1.4 degrees Fahrenheit (0.4 to 0.8 degrees Celsius) in the last century.

Most computerized climate models predict the troposphere should warm along with rising surface temperatures.

Sponsored by the National Research Council, the panel was organized to reach a consensus on this discrepancy and to determine how to interpret existing data, the accuracy of which is frequently questioned, according to panel member Frank Wentz.

No blame laid

While a combination of human activities and natural causes has contributed to rising surface temperatures, the report states, other human and natural forces may actually have cooled the upper atmosphere.

Volcanic eruptions and the prevalence of several strong El Niño events are but two factors that make it impractical to assume that a 20-year temperature rise reflects any long-term trend.

"The differences between the surface and upper-air trends in no way invalidates the conclusion that the Earth's temperature is rising," said John M. Wallace, chair of the panel and professor of atmospheric sciences at the University of Washington in Seattle. "But the rapid increase in the Earth's surface temperature over the past 20 years is not necessarily representative of how the atmosphere is responding to long-term, human-induced changes."

Wallace said world leaders should "develop an improved climate monitoring system to resolve uncertainties in the data and provide policymakers with the best available information."

Global atmospheric temperatures have been monitored by satellite since 1979 with Microwave Sounding Units on the NOAA's TIROS-N series of polar-orbiting weather satellites (see accompanying image).

But existing satellite sensors are designed to measure day-to-day changes in the weather and are ill-suited for long-term climate modeling, Wentz said. "What we're recommending is a whole new generation of satellite sensors."

The study, funded by NOAA and the Aluminum Corporation of America, was released at a meeting of the American Meteorological Society.

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