NCPA - National Center for Policy Analysis

Debate on Global Warming Still Heated

July 21, 2003

Man's contribution to global warming is insignificant, says Sallie Baliunas (George C. Marshall Institute).

In making this determination, the first step, she says, is to ask if the 20th century were unusually warm and the 19th century normal. To find out, past climate is queried, including times when humans emitted little carbon dioxide.

Proxy information about climate derived from many sources -- including glaciers; boreholes; coral and tree growth; etc. -- provides much information on past climate. That information indicates that the 19th century was unusually cold and the 20th century was not unusually warm. According to Baliunas:

  • The results are not without uncertainty -- proxies differ in their sensitivity to temperature, precipitation and other climate variables.
  • That makes averaging across many proxies tricky.
  • Also, no one type of proxy is widely available to make a meaningful global average.
  • A recent synthesis of more than 240 scientific articles by more than 1,000 researchers using various proxy data shows the climate in most locations was not extreme or unusual during the 20th century.
  • The warmest or most extreme climate for those locations tended to occur between the 9th century and 14th century -- the Medieval Warm Period.

The early extreme climate, occurring long before the recent increase in the air's carbon dioxide content, must have natural explanations that remain uncertain, says Baliunas.

Source: Sallie Baliunas, "Weather Debate Warms Up, But Let's Cool The Rhetoric," Investors Business Daily, July 21, 2003.


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