General Circulation Models

Several groups around the world have conducted climate modeling experiments in order to better understand the climate system, as well as its response to increasing levels of carbon dioxide and other greenhouse gases. There are a number of different climate models used to simulate atmospheric behavior, the most complex of these being three-dimensional general circulation models (GCMs). These numerical models simulate the evolution of the atmosphere through time from some initial state. The attractiveness of GCMs for climate change studies is their ability to model the evolution of the atmosphere in response to external forcing mechanisms - for example, a doubling of carbon dioxide. GCMs are the primary tool for trying to get a glimpse of what a high CO2 world might look like.

The GCMs have a number of weaknesses in their applicability to impact assessments. For instance, it is not known how a global warming will translate into temperature and precipitation changes at the regional level. However, the models reproduce spatial patterns of climate (i.e., model results give higher temperatures at the equator than at the poles), they emulate the seasonal cycles of climate, they provide "ball park" figures for potential changes in climatic variables and, finally, they have gained a great deal of scientific credibility in the non-scientific community among policymakers. GCM experiments have driven much of the concern over global warming.

GISS

UKMO

GFDL

Data Source: U.S. Environmental Protection Agency