(AP) — Satellite temperature measurements suggest that the next century will be a hot one, and bolster the conclusion that global warming is already under way, two Colorado scientists say.
An international scientific panel concluded last year that the planet is indeed getting hotter, and “the balance of evidence suggests that there is a discernible human influence on climate.”
The latest findings reinforce that and call attention to the urgency of the issue at a time when the world’s nations are trying to control pollutants that heat up the atmosphere.
In Thursday’s issue of the British journal Nature, climatologists Kevin Trenberth and James Hurrell write that satellite temperature measurements show a slight warming trend in the upper atmosphere between 1979 and 1995.
Previous analyses of those satellite measurements suggested a cooling of about 0.09 degrees Fahrenheit per decade during that period.
If the two National Center for Atmospheric Research scientists are correct, they have resolved a troubling discrepancy: Ground-level records show a temperature increase of 0.13 degrees Celsius between 1979 and 1995, while satellite readings higher in the atmosphere show a cooling trend during the same period.
Trenberth and Hurrell contend those atmospheric measurements were erroneous because they failed to account for inconsistencies that occurred when old satellites wore out and were replaced by new ones. During the 18-year span, eight satellites were used to measure temperature in the upper troposphere, an atmospheric layer about five miles above the ground.
To ensure consistency, each satellite in the series was supposed to have an orbit identical to its predecessor. But the satellite orbits vary somewhat, Trenberth said, and that affects the temperature readings.
“Those kinds of problems are very difficult to correct for,” Trenberth said.
When he and Hurrell examined the satellite record, they found noticeable temperature dips in 1981 and 1991. Both dips came at times when temperature measurements were being transferred from one satellite to another. When those dips are accounted for, the temperatures show a slight increase, rather than a decrease.
The accumulated evidence suggests that there should be a small positive trend, the researchers said.
John Christy, a climatologist at the University of Alabama in Huntsville who is familiar with the satellite measurements, asserted that the data are sound and that the Colorado researchers made several errors in their analysis.
Most serious is their failure to account for overlapping in the satellite measurements, he said. With every satellite switch, Christy said, both the old and new spacecraft are used for a time to make sure there’s no discrepancy.
“I can check if a new satellite affects the record or not. And it does not affect the record,” Christy said.
The debate over the satellite measurements comes at a crucial time. As scientists become more certain that the burning of fossil fuels is warming the climate, diplomats are trying to decide whether to curb such consumption.
At a meeting in Bonn last week, 150 nations discussed controlling emissions of carbon dioxide, the most abundant of the greenhouse gases.
Three more meetings are scheduled this year, two in Bonn and a final meeting in Kyoto, Japan, in December that will attempt to set targets for reducing greenhouse gas emissions after 2000.