Ranking climate models by performance using actual values and anomalies: Implications for climate change impact assessments

Reducing uncertainty in climate projections can involve giving less credence to Atmosphere‐Ocean General Circulation Models (AOGCMs) for which the simulated future climate is judged to be unreliable. Reliability is commonly assessed by comparing AOGCM output with observations. A desirable property of any AOGCM skill score is that resulting AOGCM‐performance rankings should show some consistency when derived using observations from different time periods. Notably, earlier work has demonstrated inconsistency between rankings obtained for 20‐year periods in the 20th century based on global and regional comparisons of simulated and observed near‐surface temperature anomalies. Here, we demonstrate that AOGCM‐performance rankings derived from actual temperatures, which incorporate AOGCM biases in climatological means, can be used to identify AOGCMs that perform consistently well or poorly across multiple 20‐year periods in the 20th century. This result supports the use of comparisons of simulated and observed actual values of climate variables when assessing the reliability of AOGCMs.