Warming may be happening faster in the Earth’s atmosphere than on its surface, according to a new look at old data1.

The study’s conclusion could eliminate a primary sticking point in the debate about the existence of global warming. But its methods are being called into question.

Previously, those investigating satellite temperature data gathered since 1978 concluded that the troposphere, the lowermost 8-11 kilometres of the atmosphere, has not warmed significantly. Meanwhile, temperatures at the Earth’s surface have been rising at around 0.017 ºC per year. This discrepancy has led some researchers and policy-makers to doubt that the world is warming.

Now a new analysis of satellite data from 1978 to 2002 indicates that troposphere temperature has risen by around 0.024 ºC per year, outpacing warming at the surface. So say Konstantin Vinnikov, of the University of Maryland in College Park, and Norman Grody, of the National Oceanic and Atmospheric Administration (NOAA) in Washington DC.

“This will increase the pressure on policymakers for action on greenhouse gas emissions if it is accepted by the research community,” says atmospheric scientist John M. Wallace of the University of Washington in Seattle.

That acceptance does not seem to be forthcoming. Frank Wentz’ team at Remote Sensing Systems in Santa Rosa, California, estimates there is a small warming trend of around 0.01 ºC per year. And having scrutinized satellite data for more than a decade, John Christy and Roy Spencer of the University of Alabama in Huntsville reckon that the troposphere’s temperature has remained fairly steady.

Spencer argues that the new study disregards an important adjustment that other researchers have taken into account. As a satellite ages, its orbit begins to sag, bringing instruments on its underside closer to Earth, changing the angle at which sunlight hits them and heating them.

“This results in a false warming signal,” Spencer explains. The University of Alabama has issued a press release criticizing Vinnikov and Grody’s study.

Grody disagrees: “Calibration alone would not explain the differences.” The discrepancy is in the analyses, he argues.

Happily, all camps agree that satellite data is the best way to settle the question of the troposphere’s key role in global warming. At the end of October, the National Climate Data Center in Asheville, North Carolina, is sponsoring a workshop with the goal of resolving the matter.