As nearly as climatologists can tell by studying measurements dating back to the 1850s, the earth's average surface temperature has risen by about one degree Fahrenheit over the last century. But measurements made by orbiting satellites have suggested that the lower atmosphere is cooling, leading some skeptics to argue that the world is not warming. Two scientists in California have re-analyzed the two decade record of satellite data and concluded that it has been distorted by the inevitable decay or lowering, of the satellite's orbits as they encounter atmospheric resistance. Once this error is corrected, the scientists reported, the satellite record shows the atmosphere has become warmer, but not as much as the surface has.