What is a GCM Model – General Circulation Models?
Numerical models (General Circulation Models or GCMs) represent physical processes in the atmosphere, ocean, cryosphere, and land surfaces. These models are the most advanced available tool to simulate the response of a global system in increasing greenhouse gas concentrations.nnWhile simpler models have also been used to provide average global -or regional – climate response estimates, only GCM models, possibly in conjunction with regional models, have the potential to provide geographically and physically consistent estimates of regional change required in impact analyses.nnnGCM models represent climate, using a three-dimensional mesh over the globe (see below), typically having a horizontal resolution of between 250 and 600 km, 10 to 20 vertical layers in the atmosphere and sometimes as many as 30 layers in the ocean. Their resolution is then quite crude at an exposure scale in most greenhouse gas impact assessments.nnnnnn
nnIn addition, many physical processes, such as cloud-related processes, also occur on much smaller scales and cannot be modeled properly. Instead, their known properties should be averaged on a larger scale in a technique known as parametrization. This is a great source of uncertainty in GCM-based simulations of future climate.nnSource: http://www.ipcc-data.org/guidelines/pages/gcm_guide.htmlnnn