NCPA - National Center for Policy Analysis

Climate Change Science

June 7, 2001

A research committee of the National Academy of Sciences asked by President Bush to review the state of the science on global climate change yesterday announced it was releasing its report. The 40-page report by the Committee on the Science of Climate Change, entitled "Climate Change Science: An Analysis of Some Key Questions," was not immediately available.

"We know that greenhouse gases are accumulating in Earth's atmosphere, causing surface temperatures to rise," said committee chair Ralph Cicerone, chancellor, University of California at Irvine. "We don't know precisely how much of this rise to date is from human activities, but based on physical principles and highly sophisticated computer models, we expect the warming to continue because of greenhouse gas emissions."

Although none of the information is new, according to an NAS statement the scientists emphasized the uncertainties in the science and the need for further research.

  • Measurements show that temperatures at the Earth's surface rose by about 1 degree Fahrenheit (about .6 degrees Celsius) during the 20th century.
  • The scientific community thinks the last half-century's global warming is likely the result of increases in greenhouse gases -- including carbon dioxide and methane -- in the atmosphere.
  • As previously reported by the Intergovernmental Panel on Climate Change (IPCC), computer models suggest that average global surface temperatures will rise between 2.5 and 10.4 degrees Fahrenheit (1.4 and 5.8 degrees Celsius) by the end of the 21st century.
  • Both carbon dioxide and methane -- gases that both occur naturally and are released by human activities -- are more abundant in the atmosphere now than at any time during the 400,000-year ice core record, says the NAS.

However, uncertainties remain because of the level of natural variability inherent in the climate, the questionable ability of models to simulate natural variability on centuries-long time scales, and the degree of confidence that can be placed on estimates of temperatures going back thousands of years.

Source: News Release, "Leading Climate Scientists Advise White House on Global Warming," June 6, 2001, National Academy of Sciences.


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