Working Group I: The Scientific Basis

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10.1.1 Summary of SAR

The analysis of regional climate information in the SAR (Section 6.6 of Kattenberg et al., 1996) consisted of two primary segments. In the first, results were analysed from an intercomparison of AOGCM experiments over seven large (sub-continental) regions of the world. The intercomparison included AOGCMs with and without ocean flux correction and focused on summer and winter precipitation and surface air temperature. Biases in the simulation of present day climate with respect to observations and sensitivities at time of greenhouse gas (GHG) doubling were analysed. A broad inter-model range of regionally averaged biases and sensitivities was found, with marked inter-regional variability. Temperature biases were mostly in the range of ±5ºC, with several instances of larger biases (even in excess of 10°C). Precipitation biases were mostly in the range of ±50%, but with a few instances of biases exceeding 100%. The range of sensitivities was lower for both variables.

The second segment of the analysis focused on results from nested RCMs and statistical downscaling experiments. Both these techniques were still at the early stages of their development and application, so that only a limited set of studies was available. The primary conclusions from these studies were that (a) both RCMs and downscaling techniques showed a promising performance in reproducing the regional detail in surface climate characteristics as forced by topography, lake, coastlines and land use distribution; and (b) high resolution surface forcings can modify the surface climate change signal at the sub-AOGCM grid scale.

Overall, the SAR placed low confidence in the simulation of regional climate change produced by available modelling tools, primarily because of three factors:

  • errors in the reproduction of present day regional climate characteristics;
  • wide range in the simulated regional climatic changes by different models;
  • need to more comprehensively use regionalisation techniques to study the sub-AOGCM grid scale structure of the climate change signal.

Other points raised in the SAR were the need for better observational data sets for model validation at the regional scale and the need to examine higher order climate statistics.

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