The Greenhouse Effect and Climate Change - General Circulation Models

The science of global atmospheric change is still in its infancy. Most of our images of the world's environmental future must come from computer and mathematical models. The most highly developed tools now available to project climatic changes are complex computer models called general circulation models (GCMs). Even these models are crude, imperfect representations of the real world and of the future world. They cannot indicate where changes will be the worst. Nor can they accurately calculate the heat reflected by clouds or absorbed by the ocean. As a result, scientists disagree over whether the forecasts of global warming are reliable.

Although computer models have become more accurate over the years, important uncertainties limit their predictive abilities. Even the most powerful computers are limited in their ability to store and analyze the vast quantity of data required to accurately simulate the global climate. Modelers have tried to overcome these limitations by introducing assumptions into their models that deliberately oversimplify some operations to free the GCMs' capacity for more critical operations. For example, modelers have assumed that the ocean was not warmed by emissions of greenhouse gases before 1985. Although this assumption increases GCM capacity, it increases the uncertainty of the computer's predictions because the ocean will reach its capacity to absorb emissions sooner. Scientists do not know, however, how much or by how long the predictions are distorted because of this error.

In Global Deception: The Exaggeration of the Global Warming Threat (Washington, DC: Center for the Study of American Business, Washington University, 1997), Patrick J. Michaels claims that the global warming crisis has been greatly overstated. He notes that newer GCMs, which are more physically realistic than the older models, tend to forecast less warming rather than more.