Whilst a lot of attention has been given to changing temperatures, changes in precipitation are also important. Models of the climate are used to estimate future changes in precipitation.

Simulation of 20th Century Precipitation

Climate models are used to calculate what changes in climate will occur due to natural and artificial “forcing”. The models are often referred to by the letters GCM (Global/General Circulation/Climate Models) or AOGCM (Atmosphere-Ocean coupled GCM). Confidence in the conclusions of the models depends, in part, on how well they have simulated changes in the past.

IPCC Technical Assessment Report - Precipitation

The IPCC Technical Assessment Report 4 (TAR4) presents a graph (Figure 1) showing the average results of precipitation simulations using 8 models. The graph is for global mean precipitation adjusted so that the average for the period 1961 to 1990 is zero. It covers the period 1940 to 1998.
Figure 1: Simulation and Observed Anomalies