Historical Overview

General circulation models (GCMs) are computer simulations of the motions of the Earth's atmosphere. They are among the chief tools of modern climate science.

We divide the history of GCMs into four periods, ending with the emergence of coupled ocean-atmosphere GCMs in the 1980s:

Brief overview of GCM history

The idea of simulating atmospheric motions mathematically, to aid in forecasting the weather, dates to the work of Lewis Fry Richardson in the 1920s. But it was not until the 1950s, with the advent of electronic digital computers, that numerical weather forecasting became possible as a practical matter. By the late 1950s, weather forecasters in the United States and parts of Europe incorporated computer-generated weather maps into their work on a routine basis.

In the 1960s, increasing computer power made it possible to go beyond regional weather simulations to model the global general circulation. This, in turn, allowed scientists to simulate climate, or the average state of the atmosphere over long periods (decades to centuries). GCMs began to spread from one laboratory to another in the United States, Europe, Australia, and elsewhere. The pattern of their movement is documented here in the GCM Family Tree.

By the 1970s, general circulation models (GCMs) had become the central tool of climate science. Climatology &emdash; previously focused on local and regional data collection and statistical analysis &emdash; was transformed into a global science. Around the same time, climate scientists became concerned about the possible long-term effects of carbon dioxide accumulation in the atmosphere. This combination set the stage for the study of anthropogenic (human-induced) global climate change. GCM simulations provided a crucial means of analyzing the effects of climate change.

Meanwhile, ocean modelers were beginning to build similar computer simulations of the oceanic general circulation (OGCMs). Since the oceans are a major component of the overall climate system, climate modelers began to try to "couple" OGCMs with atmospheric GCMs. Although some difficulties with linking OGCMs and AGCMs remained to be resolved, by the mid-1980s such coupled models, or OAGCMs, had established a new standard for climate modeling.

In the 1980s, scientific concerns led to international political negotiations over how to respond to climatic change. A global body of climate scientists, the Intergovernmental Panel on Climate Change (IPCC), was formed to provide scientific advice to these negotiations. In 1992, most of the world's nations signed the United Nations Framework Convention on Climate Change (FCCC). At subsequent meetings, parties to the FCCC have hammered out agreements on emissions reductions and other ways of mitigating the effects of climate change.

GCMs have thus played a major role not only in advancing atmospheric science, but in creating global awareness of a possibly serious threat to human societies.

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