Global coupled atmosphere-ocean models, similar to those used for seasonal predictions, are the fundamental scientific tools used to simulate the possible modifications of the future climate in response to anthropogenic modifications of the environment, such as different scenarios of increase in greenhouse gases concentrations.
However before applying them in such projections, the coupled models need to be carefully evaluated (in scientific terms this is referred to as verification) in simulations of the recent climate with the observed historical evolution of environmental conditions (greenhouse gases concentrations, aerosols, and possibly solar and volcanic activity, and land-use) over the past century.
The coupled system model can then be applied for performing simulations over the future century for different evolutions in the concentration of greenhouse gases and aerosols based on assumptions on the future economic development and the resulting changes. A few scenarios of economic development have been considered by the IPCC recently (SRES scenarios A2, A1B, B1) and translated into evolution of greenhouse gases and aerosols concentrations by means of Impact Assessment models with simplified representations of climate and chemistry. In response to the subsequent evolution of the radiative forcing coupled global models simulate the resulting modification of the atmospheric and oceanic circulations and climate. The time series generated by these coupled simulations are carefully sampled and stored in international databases for their application in various impact studies, or as lateral boundary conditions for driving higher resolution regional models.
Annual global mean surface air temperature evolution (°C) over the 21st century simulated in the A1B (top) and B1 (bottom) scenarios by the ENSEMBLES climate models. Temperature increases above the long-term average for 1961-1990 are shown.