A National Research Council (NRC) report indicates that despite differences in temperatures of the lower atmosphere and the earth's surface, strong evidence exists that warming of the earth's surface is "undoubtedly real."

The report, released during the annual meeting of the American Meteorological Society in Long Beach, CA, examines the apparent conflict between surface and upper-air temperature, which has led to controversy over whether global warming is actually occurring.

The earth's surface temperature has risen about 0.7° to 1.4°F in the last century, according to the report. However, data from satellites and weather balloons since 1979 indicate little, if any, warming of the low- to mid-troposphere, the atmosphere extending up to about five miles above the earth's surface.

Climate models generally predict that temperatures should increase at these upper-air levels as well as at the surface if increased greenhouse gases are causing the warming.

"The differences between the surface and upper-air trends in no way invalidates the conclusion that the earth's temperature is rising," said John Wallace, chair of the 11-member panel that wrote the report and professor of atmospheric sciences at the University of Washington in Seattle.

"But the rapid increase in the earth's surface temperature over the past 20 years is not necessarily representative of how the atmosphere is responding to long-term, human-induced changes, such as increasing amounts of carbon dioxide and other greenhouse gases. The nations of the world should develop an improved climate-monitoring system to resolve uncertainties in the data and provide policymakers with the best available information."