NCPA - National Center for Policy Analysis

Global Warming "Science" Needs Testing

July 8, 2003

Very little is known about the causes, effects and extent of climate change, says James Schlesinger, former secretary of energy under Jimmy Carter.

Yet in recent years the inclination has been to attribute global warming to a single dominant cause -- the increase in greenhouse gases. But climate has always been changing -- and sometimes the swings have been rapid, says Schlesinger.

  • Since the start of the 20th century, the mean temperature at the earth's surface has risen about 1 degree Fahrenheit.
  • The level of carbon dioxide (CO2) in the atmosphere has been increasing for more than 150 years.
  • CO2 is a greenhouse gas -- and increases in it, other things being equal, are likely to lead to further warming.
  • It was followed by a cooling trend from 1940 to around 1975.
  • Yet the concentration of greenhouse gases was measurably higher in that later period than in the former.
  • That drop in temperature came after what was described in the National Geographic as "six decades of abnormal warmth."

According to Schlesinger, we cannot tell how much of the recent warming trend can be attributed to the greenhouse effect and how much to other factors. Consequently, any approach to policy formation under conditions of such uncertainty should be taken only on an exploratory and sequential basis.

Source: James Schlesinger, "Climate Change: The Science Isn't Settled," Washington Post, July 7, 2003.


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