LOS ANGELES (Aug. 14) - Scientists who argue against global warming often cite nearly 20 years of satellite readings showing slight cooling of the atmosphere two miles up. But a new study indicates those readings are incorrect.
The new findings, however, do nothing to settle the debate over whether global warming is really occurring.
Scientists on both sides agree that Frank Wentz, a physicist and chief executive of Remote Sensing Systems in Santa Rosa, pinpointed the problem with the satellite temperature readings. But that's as far as they agree.
They continue to debate how the temperatures should be revised and what the revisions mean. No one is changing his or her overall position.
Those who reject the notion that manmade warming of the Earth is occurring say the revised temperatures make an insignificant change. Those who believe that carbon dioxide and industrial gases are heating the atmosphere say the revisions now show a slight warming trend, in line with the warming of the Earth's surface.
In the study in Thursday's issue of the journal Nature, Wentz found that the orbit of satellites that take temperature readings decreases over time because of atmospheric drag on the spacecraft. They drop a bit more than half a mile every year, and twice that during some years.
As the satellite slows and drops, the onboard instrument perceives the temperatures below it as cooling, Wentz found.
The perceived temperature change "was just an artifact of the altitude changing," he concluded.
When Wentz recalculated the readings from 1979 to 1995, he found temperatures in the lower atmosphere are more in line with rising temperatures at Earth's surface and rising temperatures just a few miles higher in the atmosphere.
Before the correction, scientists were confounded because temperatures in the lower troposphere, the region from the ground to about 2 miles up, seemed to be cooling .09 degrees per decade, while the middle to upper troposphere - a region centered about 4 miles up - seemed to be warming .05 degrees every decade.
But when Wentz and co-author Matthias Schabel took the falling satellite effect into account, they found the lower troposphere was warming 0.13 degrees per decade.
In an accompanying commentary, Dian J. Gaffen of the National Oceanographic and Atmospheric Administration's Air Resources Laboratory in Silver Spring, Md., cautioned against "making too much of these new indications of warming" because the satellite data covers a short period and other factors could be at work.
In the latest issue of the journal Science, James Hansen and colleagues at NASA's Goddard Institute for Space Studies wrote that Wentz's work helps reconcile temperature trends that didn't make sense.
With the correction, "it's very hard for anyone to look at any data and deny the reality of global warming. In a sense, it was the last refuge of those who would deny that there's global warming," Hansen said.
Patrick Michaels, a professor of environmental sciences at the University of Virginia in Charlottesville and a global warming skeptic, isn't convinced.
Wentz "came up with no real change that's appreciable" in the satellite data, he said, and temperature readings from instruments on helium balloons also haven't found significant warming.
John Christy, a professor of atmospheric science at the University of Alabama in Huntsville who did the original work with the satellite data, said that when he corrected his data to account for Wentz's findings and some other factors, he found only an insignificant change - "no cooling, no warming."
Comments on this posting?
Click here to post a public comment on the Trash Talk Bulletin Board.
Click here to send a private comment to the Junkman.
Copyright © 1998 Steven J. Milloy. All rights reserved on original material. Material copyrighted by others is used either with permission or under a claim of "fair use." Site developed and hosted by WestLake Solutions, Inc.
Material presented on this home page constitutes opinion of Steven J. Milloy.