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 past two decades and had cooled in the tropics.
Now two independent studies have found errors in the 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 Thursday in the online edition of the journal Science.
The scientists who developed the original troposphere temperature records from satellite data, John Christy and Roy Spencer of the University of Alabama, Huntsville, conceded Thursday 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,” Christy said. “We still have this modest warming.”
Other climate experts, however, said that the new studies were very significant, effectively solving a puzzle that had been used by opponents of curbs on heat-trapping greenhouse gases.
Until recently, Christy and Spencer were the only scientists who had scrutinized data from weather satellites to see if they could indirectly deduce the temperature of several layers within the troposphere, which extends up about 5 miles.
They and other scientists have also tried to analyze temperature readings gathered by about 700 weather balloons lofted twice a day around the world.
But the satellites’ orbits shift and sink over time, their instruments are affected by sunlight and darkness, and data has to be calibrated to account for eccentricities of sensitive instruments.