Transient climate simulation

This may be contrasted with an equilibrium climate simulation in which greenhouse gas concentrations are suddenly changed (typically from pre-industrial values to twice pre-industrial values) and the model allowed to come into equilibrium with the new forcing.

Early GCMs used "swamp" or "slab" ocean models for reasons of computational simplicity.

If the simulation is partly of the past, observed CO2 levels may be used (and perhaps solar variation, and volcanic forcing).

The transient simulation is intended to be a physically plausible path for the climate system to follow.

Although (given natural variability) even a perfect model would not simulate the year-to-year variations seen in the real world, in an ideal model the variation from decade to decade would track that of the real world.