NCPA - National Center for Policy Analysis

The Limitations of Climate Models

May 20, 2002

The General Circulation Models and Global Climate Models (GCMs) that world leaders are using to make critical decisions regarding global climate change are limited in important ways, including the inability to reproduce important atmospheric phenomena, and accurately represent complex natural interconnections.

Because of these and other limitations, GCMs simply cannot reliably reproduce climate systems, say experts.

  • In addition, the data used to determine global average temperature is measured by three different instruments -- ground-based thermometers, weather balloons and global satellite observations -- with each system covering a slightly different range of the earth's atmosphere and providing conflicting results.
  • For instance, both the global satellite network and weather balloon observations show a modest cooling trend during the past 25 years, the ground-based thermometers show a modest warming of approximately 0.13 degrees Celsius per decade.
  • The GCMs show global temperatures rising across all levels of the atmosphere; but the lowest predicted global temperature measurement of the GCMs is nearly three times more than the temperature rise measured by ground-based thermometers reflected in reality. [See figure.]
  • Furthermore, the GCMs do not reflect the temperature differences or the direction of temperature change within various levels of the atmosphere, nor do they show the actual amount of temperature change.

While GCMs cannot be expected to simulate future weather, they should be able to accurately depict the earth's present climate and vitality. Since they cannot, GCM predictions of climate change are statistical exercises with little bearing on reality.

Source: David R. Legates (Director Center for Climatic Research University of Delaware Newark and NCPA adjunct scholar), "Limitations of Climate Models as Predictors of Climate Change," Brief Analysis No. 396, May 17, 2002, NCPA.

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