The climatic effects of biomass burning: investigations with a global climate model

A global climate model, the National Center for Atmospheric Research (NCAR) Climate System Model (CSM), has been used to evaluate direct, indirect, and transport effects of the smoke from biomass burning. Biomass smoke distributions were estimated via a seasonally-varying source function that produced monthly mean estimates of the flux of trace gases to the atmosphere which were then confirmed qualitatively using satellite observations. The direct effect was modeled by assuming new cloud fractions wherever biomass smoke occurred. A sensitivity study was conducted to determine the most appropriate way to add these new ‘cloudsʹ. An indirect effect on existing clouds was modeled by reducing the cloud optical depth (which increases reflectivity) when they coincided with biomass smoke. Advection of the smoke has been accomplished by adding it as a tracer in the NCAR CCM3 (the atmospheric component of CSM). Preliminary results yield surface temperature reductions of several degrees and heating of the mid-levels of the atmosphere in the vicinity of major smoke emissions.