Slide 20: How many GCMs are there?
Considering the incredible computing power necessary to run a full GCM, one would expect there to be only a few models.
In fact, a number of different groups have developed and refined models over the years, and the IPCC Third Assessment Report uses no fewer than 34 AOGCMs, some of which exist in several refinements.
These models are developed and operated by 18 different climatology centres, including the UK Meteorological Centre, National Center for Atmospheric Research, Goddard Institute for Space Studies and the Geophysical Fluid Dynamics Laboratory.
These models are run nearly constantly, and the results are published on the internet in order to allow planners and response modellers ready access.