NCPA - National Center for Policy Analysis

Selective Science In Global Warming Claims

December 20, 2000

Environmental groups have used selective science and inaccurate news reports to demand that the United States accede to international demands for drastic, immediate action to reduce greenhouse gas emissions.

However, a closer look shows there are uncertainties in the studies they use, while other studies cast doubt on the need for immediate emission cuts. For example,

  • In the July 14 issue of "Science," Thomas Crowley of Texas A & M University concluded the 20th century has been the warmest century of the past 1,000 years and that greenhouse gas emissions from human energy use are responsible for as much as 75 percent of this warming.
  • Crowley used data from tree rings and ice core boreholes to construct estimates of temperature trends, saying that previous studies using such data were hampered by "inadequate lengths of the time series being evaluated."
  • However, in an analysis published by the NCA that looks at temperature records over even longer periods, David Deming of the University of Oklahoma points out that Earth's average temperature was higher than at present for more than 7,500 of the past 10,000 years (see figure).
  • Indeed, borehole measurements indicate Earth was as much as 1.5 degrees Fahrenheit warmer for 5,000 of those years.

These examples show that the base period selected can affect projections of future global temperature trends. Such projections are even more uncertain when applied to specific regions of the Earth, where computer models have yielded contradictory or ambiguous results.

Source: H. Sterling Burnett (senior policy analyst, NCPA), "Cooling Overheated Global Warming Rhetoric," Brief Analysis No. 345, December 20, 2000, National Center for Policy Analysis.

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