New Evidence Confirms That Earth's Surface Temperature Is Rising
Despite differences in temperature data, strong evidence exists to show that the warming of the Earth's surface is "undoubtedly real," and that surface temperatures in the past two decades have risen at a rate substantially greater than the average of the past 100 years, says a new report by the National Research Council (NRC) of the National Academies.
The report examines the apparent conflict between surface temperature and upper-air temperature, which has led to the controversy over whether global warming is actually occurring. In the last century, the Earth's surface temperature has risen 0.4 to 0.8[degrees]C--or 0.7 to 1.4[degrees]F, the report says. But data collected by satellites and balloon-borne instruments since 1979 indicate little if any warming of the low- to mid-troposphere--the atmospheric layer extending about 5 miles from the Earth's surface. Climate models generally predict that temperatures should increase in the upper air as well as at the surface if increased concentrations of 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 M. Wallace, chair of the 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."
While a combination of human activities and natural causes has contributed to rising surface temperatures, other human and natural forces may actually have cooled the upper atmosphere. For example, natural events such as the eruption of Mt. Pinatubo in 1991 have tended to decrease atmospheric temperature for several years. …