Increasing concentrations of carbon dioxide and other greenhouse gases in the air, which cause temperatures at Earth's surface to warm, will turn the upper layers of the atmosphere cooler and thinner in coming decades, new research suggests. This counterintuitive phenomenon, first predicted in the late 1980s and recently inferred from satellite data, will probably lead to longer orbital lifetimes for satellites and space junk.
Temperature trends in the highest levels of the atmosphere are difficult to measure, says Robert E. Dickinson, an atmospheric scientist at the Georgia Institute of Technology in Atlanta. He was one of the first scientists to propose a high-altitude cooling effect of greenhouse gases. Although direct temperature data aren't available, the thinning of the air at high altitudes has been detected. Dickinson notes that satellites that whiz around Earth in the upper atmosphere are experiencing less atmospheric drag than they used to.