Climate Forcing by Black and Organic Carbon: Central Values and Uncertainties

Several recent studies have estimated climate forcing by carbonaceous aerosols using available emission inventories. It is widely acknowledged that emission rates and other inputs to forcing calculations are uncertain, but estimates of confidence intervals have not been calculated rigorously. We present a preliminary analysis of minimum uncertainties in climate forcing by carbonaceous aerosols. Our forcing estimates are calculated using a global chemistry and transport model (MATCH) in conjunction with recently-developed emission inventories and radiation codes. The emission inventory [Bond et al., 2002] provides low, central and high estimates for each 1°\x1°\ grid cell that reflect uncertainties in fuel use and emission factors. Emissions are especially uncertain in regions where residential combustion contributes heavily, particularly in Asia and Eastern Europe. Other parameters varied are the time for transformation between hydrophobic and hydrophilic aerosol, the wet scavenging rate and the imaginary index of refraction. Variation in forcing due to the mixing state of the aerosol, also known to have important effects on climate forcing [Jacobson, 2001], is not included in this study and would increase the uncertainty. References Bond, T. C., D. G. Streets, S. M. Fernandes, S. M. Nelson, J.-H. Woo, and Z. Klimont, A Technology-Based Global Inventory of Black and Organic Carbon Emissions from Combustion, manuscript in preparation. Jacobson M. Z., Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols, Nature 409, 695-697, 2001.