High resolution satellite records of active fire and burned area extend now for more than a decade, allowing for improved estimates of fire emissions and a better understanding of fire-mediated feedbacks involving ecosystems, climate, and human activity. Here I describe a systematic framework for estimating global burned area and fire emissions (the Global Fire Emissions Database (GFED)) that uses Moderate Resolution Imaging Spectroradiometer observations from Terra and Aqua along with other satellite data streams as inputs to a biogeochemical model. I then use the GFED time series, with chemical transport and climate models, to assess fire effects on greenhouse gases, regional climate, and the transport of nutrients across biomes.
Results/Conclusions
Fires explained most of the interannual variability of atmospheric carbon monoxide during 1997-2007 and contributed substantially to variability of methane and carbon dioxide. In the tropics, fires at the deforestation frontier accounted for approximately one third of global emissions and were highly sensitive to year-to-year variations in the length and intensity of the dry season. In equatorial Asia, forest clearing and fire emissions increased during periods of El Nino-induced drought. During these episodes, fire-emitted aerosols created large regional smoke clouds. Simulations with the Community Atmosphere Model (CAM) showed that these aerosols simultaneously cool surface temperatures and warm the mid-troposphere. The increased atmospheric stability in the model decreased convection over source regions and intensified drought in a positive feedback loop that may have consequences for longer-term El Nino - Southern Oscillation dynamics. Another set of simulations with the GEOS-CHEM chemical transport model showed that reactive nitrogen (N) species emitted by both deforestation and savanna fires contributed to N deposition in interior tropical forests, potentially enhancing tropical forest productivity in South America, Africa, and equatorial Asia. In boreal ecosystems, black carbon emissions during high fire years deposited on snow and sea ice in downwind areas, decreasing albedo and increasing energy absorption. CAM simulations showed this subsequently accelerated snow melt and regional warming. Over the continents, an important multi-decadal legacy of fires is to regulate stand age, species composition, and surface albedo. Recent increases in burned area within North America and Eurasia have increased surface albedo during spring and summer which in turn may slow some of the climate warming caused by greenhouse gases. A key future challenge is to integrate deforestation and fire emissions estimates in climate-carbon models– this is important for assessing deforestation effects on both climate and human health.
