Air Pollution as a Climate Forcing: A Workshop

Day 2 Presentations

Global Aerosol Climatologies: Are There Differences Between Models and the Real World?

Joyce E. Penner
University of Michigan

Aerosol models are used to predict aerosol forcing. How good are the models? Do they agree with measured aerosol concentrations? This talk summarizes the results of a model intercomparison performed under the auspices of the IPCC. The results indicate that current aerosol models systematically underestimate aerosol concentrations in the atmosphere, especially in the region from 5°S to 35°S. These differences suggest that the aerosol forcing estimated by models may be an underestimate.

Results of the study are summarized below. This figure shows the difference between the forcing over oceans estimated from the mean of the models that participated in the model intercomparison exercise and 3 different analyses of forcing from the AVHRR satellite. It also shows the difference between the mean of the models and an analysis of forcing based on the ERBE satellite. There is a tendency for the models to underestimate aerosol forcing in the region from 5°S to 35°S compared to the satellites. Poleward of 25°N, the ERBE satellite analysis implies that the models overestimate forcing, while the AVHRR analysis tends to suggests that the models provide an estimate of forcing that is, on average, within 1 W/m2 of that suggested by the satellite analyses.

Zonal chart of flux differences. See capption and text for more

Figure 1: Difference between the mean of the model-predicted clear-sky shortwave flux and that from ERBE and from three different AVHRR analyses.

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