Proponents of the theory that humans are causing a dangerous change in the earth's climate base their belief on several sets of data. For instance, ground-level temperature measurements show the earth has warmed between 0.3 degrees and 0.6 degrees Celsius in the last century, and atmospheric carbon dioxide (CO2), a primary greenhouse gas, has increased by approximately 30 percent over the past 150 years.

According to computer models based on such data, the earth will warm a further 0.8 degrees to 3.5 degrees C over the next century. However, the earth's surface temperature increase during the past 150 years is far less than the best climate models predicted. And as the models improve they show less warming:

• Based on models, in 1990 the Intergovernmental Panel on Climate Change predicted an increase in temperature between 4.5 degrees and 6.0 degrees C by 2050.

• In 1996 the IPCC predicted an increase of 0.8 degrees to 3.5 degrees C by 2100 -- less than half the warming in twice the time.

• A U.S. government survey of the global climate model literature conducted predicted even less warming -- between 0.5 degrees and 2.0 degrees C by 2100 (see figure).

Yet even the improved climate models are off by more than a degree, when their predictions are compared to actual temperature data.

Furthermore, a study in the October 2, 1998, issue of Science showed that around 12,500 years ago global temperature rose by more than 20 degrees Fahrenheit in approximately 50 years. And in the March 11, 1999, issue of Nature, scientists reported that CO2 levels have varied greatly during the last 11,000 years.

Source: H. Sterling Burnett (NCPA Senior Policy Analyst), "The Collapsing Scientific Cornerstones of Global Warming Theory," Brief Analysis No. 299, June 30, 1999, National Center for Policy Analysis, 12770 Coit Rd., Suite 800, Dallas, Texas 75251, (972) 386-6272.

For text http://www.ncpa.org/ba/ba299.html