Figure 8.11. Normalised RMS error in simulation of climatological patterns of monthly precipitation, mean sea level pressure and surface air temperature. Recent AOGCMs (circa 2005) are compared to their predecessors (circa 2000 and earlier). Models are categorised based on whether or not any flux adjustments were applied. The models are gauged against the following observation-based datasets: Climate Prediction Center Merged Analysis of Precipitation (CMAP; Xie and Arkin, 1997) for precipitation (1980–1999), European Centre for Medium Range Weather Forecasts 40-year reanalysis (ERA40; Uppala et al., 2005) for sea level pressure (1980–1999) and Climatic Research Unit (CRU; Jones et al., 1999) for surface temperature (1961–1990). Before computing the errors, both the observed and simulated fields were mapped to a uniform 4° x 5° latitude-longitude grid. For the earlier generation of models, results are based on the archived output from control runs (specifically, the first 30 years, in the case of temperature, and the first 20 years for the other fields), and for the recent generation models, results are based on the 20th-century simulations with climatological periods selected to correspond with observations. (In both groups of models, results are insensitive to the period selected.)