Nature Study Fails to Dent Satellite Data

Published July 1, 2004

A study of global temperature data in the May 5 issue of Nature claims to solve a discrepancy between surface-station temperature readings and global temperature readings taken from orbital satellites. Experts reviewing the Nature study, however, say it fails to impugn the satellite readings.

Urban Heat Islands
Ever since the first temperature-reading satellite was launched in 1979, scientists have tried to explain the discrepancy between satellite and ground-based readings of global temperatures. Satellite readings have shown virtually no warming trend since 1979, while ground-based readings have registered significant warming.

According to scientific studies, the discrepancy results from an urban heat island effect. Concrete, factories, office buildings, and automobiles produce heat in and around cities, causing temperatures to be somewhat warmer than the surrounding region. Moderate warming trends at land-based weather stations, typically located at airports in and around growing cities, merely reflect the growing population of the nearby city, studies show.

The recent Nature study attempts to contest the urban heat island evidence and cast doubt on the satellite readings. To support their theory, the study’s authors introduced a “fudge factor” that attempts to explain and dismiss a significant amount of documented atmospheric cooling.

Fudging the Numbers
The fudge factor, say experts, is where the Nature authors go wrong.

“You can’t subtract more signal than is there, but that’s what they’ve done,” said Dr. Roy Spencer, a principal research scientist in the Earth System Science Center (ESSC) at the University of Alabama in Huntsville (UAH).

The problem, said Spencer, is that the study’s fudge factor removes more stratospheric cooling than actually appears in the data, thus creating a spurious warming signal.

“Simply put, this method overcorrects for stratospheric cooling,” said Dr. John Christy, a professor of atmospheric science at UAH and director of the ESSC. “We tried this same technique in the early 1990s but it didn’t work.

“Instead,” said Christy, Dr. Spencer “developed a method for accurately removing stratospheric temperatures from the data and we published that in 1992.”

According to UAH researchers, the satellite sensors show a long-term warming trend in the lower atmosphere of only about 0.08º C per decade [about 1.4º F per century] in the past 25 years. That trend has been corroborated by U.S., British, and Russian studies comparing satellite data to temperature data gathered by weather balloons.

Peer Review Lacking
“This kind of mistake would not get published with adequate peer review of manuscripts submitted for publication,” observed Spencer. “But in recent years, a curious thing has happened. The popular science magazines, Science and Nature, have seemingly stopped sending John Christy and me papers whose conclusions differ from our satellite data analysis.

“This is in spite of the fact that we are (arguably) the most qualified people in the field to review them. This is the second time in nine months that these journals have let papers be published in the satellite temperature monitoring field that had easily identifiable errors in their methodology.”

Added Spencer, “A paper claiming to falsify our satellite temperature record has been published in the ‘peer reviewed’ literature, and the resulting news reports will never be taken back. This is one reason increasing numbers of scientists regard Science and Nature as ‘gray’ scientific literature.”

James M. Taylor is managing editor of Environment & Climate News. His email address is [email protected].