Briefly describe what a Global Climate Model (GCM) is?

A GCM predicts weather conditions that prevail for years. They show characteristics weather characteristics that occur over years. They cannot give accurate weather accounts for everyday but give indications of climatic indicators.

They work with the physics equations of motion. There are four different types of climate models:
1. Energy Balance Models (EBM)
2. 1*Dimensional Radiative *Convective Models (RCM)
3. 2 - Dimensional Statistical * Dynamical Models (SDM)
4. 3- Dimensional General Circulation Models (GCM)

The EBM are simple models that deal with the radiation balance, between incoming solar radiation and heat loss, and longitudinal energy transfer. Latitudinal Characteristics are ignored when EBMs are dimensionless. If the model is one dimension then the latitude is included. The RCM can be either one or two-dimensional and the height is also considered. The SDM are two dimensional with both the horizontal and vertical dimension. The horizontal energy transfer of the energy balance model is combined with the radiative- convective functions of the radiative convective models.

The GCMs are the best tool for predicting the response of the global climate system to increasing concentrations of greenhouse gases. They are three dimensional, and involve very complicated calculations of atmospheric functions. The most complex is the coupled atmospheric ocean general circulation models (AOGCMs), because they have ten to twenty layers in the atmosphere and approximately thirty in the oceans. The data collected is taken for the whole globes therefore there are lot calculations that are carried out. This means that it is computationally intensive.

The GCM cannot give a stable equilibrium condition under the current climatic conditions. Therefore flux adjustments have been provided to make sure that can do so. These are really just non-physical correlation constants that are used to make sure models stay in track.
There are many different groups that have been developed and refined GCMs over the years, and the IPCC Third Assessment Report uses 34 AOGCMs. They are developed and operated by 18 different climatological centres

GCMs are used for a better understanding of the climatic processes, and for indicating how the physical characteristics of the earth are interacting. The allow climatologists to make informed and scientifically relevant predictions based on the their understanding and knowledge of climate. They can also help in establishing the age where the human race began when palaeoclimatological data to see the long-term climate effects. They are best tools for climate science and aid conservationists, planners and politicians to test the different response scenarios.

NCUMISA MNOTOZA
Environmental and Water Sciences
2253897@uwc.ac.za