Estimate of the climate impact of biomass burning aerosols in the Amazon by using NCAR-CCM3

It has been recognized that pollution (sulfate aerosols), and biomass burning (smoke aerosols), are the two principal anthropogenic sources that are now influencing the global climate. Researchers are currently trying to provide better estimates of the climate impact due to anthropogenic aerosols and to lower the range of uncertainty in their calculations. Estimations suggest a global-mean direct radiative forcing in the range from -0.3 to -1.0 W/m² for biomass burning aerosols, with a similar value for the indirect effect. The primary goal of this work is to estimate the global climate impact due to smoke aerosols from biomass burning using the National Center for Atmospheric Research (NCAR)-Community Climate Model, Version 3 (CCM3). Analysis of data from the AERONET project was used to define a more realistic average of the optical/radiative properties of smoke particles from biomass burning in the Amazon, and also, to provide relevant information about the cloud-aerosol interactions. This information was put into the context of the NCAR-CCM3 BATS, and then the cloud/radiative scheme of the standard model was modified to include both the direct and indirect effects of the aerosols. Our results suggest an annual global mean "total" (direct+indirect) radiative forcing of about -0.08 W/m². This value is in good agreement with recent estimations considering that we are only including the biomass burning aerosols in the Amazon region. In addition, our model simulations provide a "total" radiative forcing of about -10 W/m² for the Amazon region during the dry-season, where the indirect effect is responsible for about 80% of this value. This research hopefully will contribute to the aerosol climate modeling area by providing a scheme in which both the direct and indirect effects of the aerosol can be explicitly represented in a GCM