Validation of global climate models

(IPCC 1992 and personal experience)

• Climate models can never be completely validated. (See Oreskes, N., K. Shrader-Frechette, and K. Belitz, 1994: Verification validation, and confirmation of numerical models in the earth sciences. Science, 263, 641-645.)

• Several tests can be made of climate models against observed climate behavior, both in the recent past and in paleoclimates

• Models show considerable skill in reproducing large-scale distribution of surface pressure, temperature, wind, and precipitation in both summer and winter.

• On regional scales (sub-continent) all models show significant departures from observations for both temperature and precipitation.

• Soil moisture comparisons are limited by lack of data, but results, where data are available, are in qualitative agreement.

• Snow cover is reasonably well simulated, except where temperatures are too high (e.g., high latitudes in NH)

• Radiative fluxes at the top of the atmosphere are simulated well in some models.

• Daily and interannual variability is mixed. Most models show good results for some locations, but not good in others.

• Model response is good for slow changes in forcing such as El Nino, Mt. Pinatubo, wet and dry periods in the Sahel, and select periods from the last 18,000 years.

• Ocean models reproduce large-scale features fairly well

• Coupled atmosphere/ocean models do reasonably well in simulations of the last ice age.