Errors Cited in Assessing Climate Data

New York Times
August 12, 2005
By Andrew Revkin

Some scientists who question whether human-caused global warming poses a threat have long pointed to records that showed the atmosphere's lowest layer, the troposphere, had not warmed over the last two decades and had cooled in the tropics.

Now two independent studies have found errors in the complicated calculations used to generate the old temperature records, which involved stitching together data from thousands of weather balloons lofted around the world and a series of short-lived weather satellites.

A third study shows that when the errors are taken into account, the troposphere actually got warmer. Moreover, that warming trend largely agrees with the warmer surface temperatures that have been recorded and conforms to predictions in recent computer models.

The three papers were published yesterday in the online edition of the journal Science.

The scientists who developed the original troposphere temperature records from satellite data, John R. Christy and Roy W. Spencer of the University of Alabama in Huntsville, conceded yesterday that they had made a mistake but said that their revised calculations still produced a warming rate too small to be a concern.

"Our view hasn't changed," Dr. Christy said. "We still have this modest warming."

Other climate experts, however, said that the new studies were very significant, effectively resolving a puzzle that had been used by opponents of curbs on heat-trapping greenhouse gases.

“These papers should lay to rest once and for all the claims by John Christy and other global warming skeptics that a disagreement between tropospheric and surface temperature trends means that there are problems with surface temperature records or with climate models,” said Alan Robock, a meteorologist at Rutgers University.

The findings will be featured in a report on temperature trends in the lower atmosphere that is the first product to emerge from the Bush administration's 10-year program intended to resolve uncertainties in climate science.

Several scientists involved in the new studies said that the government climate program, by forcing everyone involved to meet five times, had helped generate the new findings.

"It felt like a boxing ring on occasion," said Peter W. Thorne, an expert on the weather balloon data at the Hadley Center for Climate Prediction and Research in Britain and an author of one of the studies.

Temperatures at thousands of places across the surface of the earth have been measured for generations. But far fewer measurements have been made of temperatures in the air from the surface through the troposphere, which extends up about five miles.

Until recently Dr. Christy and Dr. Spencer were the only scientists who had plowed through vast volumes of data from weather satellites to see if they could indirectly deduce the temperature of several layers within the troposphere.

They and other scientists have also tried to analyze temperature readings gathered by some 700 weather balloons lofted twice a day around the world.

But each of those efforts has been fraught with complexities and uncertainties.

The satellites' orbits shift and sink over time, their instruments are affected by sunlight and darkness, and data from a succession of satellites has to be calibrated to account for eccentricities of sensitive instruments.

Starting around 2001, the satellite data and methods of Dr. Christy and Dr. Spencer were re-examined by Carl A. Mears and Frank J. Wentz, scientists at Remote Sensing Systems, a company in Santa Rosa, Calif., that does satellite data analysis for NASA.

They and several other teams have since found more significant warming trends than the original estimate.

But the new paper, by Dr. Mears and Dr. Wentz, identifies a fresh error in the original calculations that, more firmly than ever, showed warming in the troposphere, particularly in the tropics.

The error, in a calculation used to adjust for the drift of the satellites, was disclosed to the University of Alabama scientists at one of the government-run meetings this year, Dr. Christy said.

The new analysis of data from weather balloons examined just one possible source of error, the direct heating of the instruments by the sun.

It found that when data were examined in a way that accounted for that effect, the temperature record produced a warming, particularly in the tropics, again putting the data in line with theory.

"Things being debated now are details about the models," said Steven Sherwood, the lead author of the paper on the balloon data and an atmospheric physicist at Yale. "Nobody is debating any more that significant climate changes are coming."

NOTICE: In accordance with Title 17 U.S.C. Section 107, this material is distributed without profit to those who have expressed a prior interest in receiving this information for research and educational purposes.

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