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Global Modeling of Tropospheric Aerosols and Their Contribution to Climate Variation

Catherine C. Chuang, PI
Keith E. Grant, Co-I

Abstract: Atmospheric aerosols have significant effects on climate through their impact on the Earth's radiation budget. Part of our earlier studies have been focused on developing an understanding of global and regional sulfate aerosol abundances and investigating their direct and indirect climate effects with a fully coupled climate-aerosol model. Our simulations have indicated that the anthropogenic sulfate aerosols may decrease the globally-averaged solar radiation absorbed by the Earth-atmosphere system through the direct effect by about -0.4 Wm-2. With different approaches for the formation of anthropogenic sulfate and its relation to aerosol size distribution, the indirect forcing may range from -0.6 to -1.6 Wm-2. This range reduces to -0.4 to -1.1 Wm-2 if a prescribed marine background particle number concentration is universally applied over the ocean.

To address the radiative impact of other significant aerosol types on climate, we have developed emission inventories for carbonaceous and dust aerosols. We have also developed a unique annual emission inventory of anthropogenic SO2 for the years 1950 through 1994. Moreover, we have modeled aerosol optical properties to account for changes in the refractive indices with relative humidity and dry aerosol composition and developed parameterizations of cloud response to aerosol abundance to evaluate the importance of aerosol/cloud interactions on climate forcing. Based on our strength in this area, we propose to extend our previous effort to simulate the global distributions of all the important aerosol species and to assess their potential to mask part of the warming expected from greenhouse gas emissions. We will also examine the difference in forcing pattern and magnitude by direct and indirect aerosol effects and determine the relative contribution of industrial and non-industrial anthropogenic sources. The goal of this proposal is to study the global aerosol cycle and to make a more quantitative evaluation of the effects of aerosol emissions on the Earth's climate.

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