We present a methodology for estimating the seasonal and interannual variation of biomass burning designed for use in global chemical transport models. The average seasonal variation is estimated from 4 years of fire‐count data from the Along Track Scanning Radiometer (ATSR) and 1–2 years of similar data from the Advanced Very High Resolution Radiometer (AVHRR) World Fire Atlases. We use the Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) data product as a surrogate to estimate interannual variability in biomass burning for six regions: Southeast Asia, Indonesia and Malaysia, Brazil, Central America and Mexico, Canada and Alaska, and Asiatic Russia. The AI data set is available from 1979 to the present with an interruption in satellite observations from mid‐1993 to mid‐1996; this data gap is filled where possible with estimates of area burned from the literature for different regions. Between August 1996 and July 2000, the ATSR fire‐counts are used to provide specific locations of emissions and a record of interannual variability throughout the world. We use our methodology to estimate mean seasonal and interannual variations for emissions of carbon monoxide from biomass burning, and we find that no trend is apparent in these emissions over the last two decades, but that there is significant interannual variability.

[1] We present an assessment of biofuel use and agricultural field burning in the developing world. We used information from government statistics, energy assessments from the World Bank, and many technical reports, as well as from discussions with experts in agronomy, forestry, and agro-industries. We estimate that 2060 Tg biomass fuel was used in the developing world in 1985; of this, 66% was burned in Asia, and 21% and 13% in Africa and Latin America, respectively. Agricultural waste supplies about 33% of total biofuel use, providing 39%, 29%, and 13% of biofuel use in Asia, Latin America, and Africa, and 41% and 51% of the biofuel use in India and China. We find that 400 Tg of crop residues are burned in the fields, with the fraction of available residue burned in 1985 ranging from 1% in China, 16-30% in the Middle East and India, to about 70% in Indonesia; in Africa about 1% residue is burned in the fields of the northern drylands, but up to 50% in the humid tropics. We distributed this biomass burning on a spatial grid with resolution of 1°Â 1°, and applied emission factors to the amount of dry matter burned to give maps of trace gas emissions in the developing world. The emissions of CO from biofuel use in the developing world, 156 Tg, are about 50% of the estimated global CO emissions from fossil fuel use and industry. The emission of 0.9 Pg C (as CO 2 ) from burning of biofuels and field residues together is small, but nonnegligible when compared with the emissions of CO 2 from fossil fuel use and industry, 5.3 Pg C. The biomass burning source of 10 Tg/yr for CH 4 and 2.2 Tg N/yr of NO x are relatively small when compared with total CH 4 and NO x sources; this source of NO x may be important on a regional basis.

[1] We investigate the impact of climate change on wildfire activity and carbonaceous aerosol concentrations in the western United States. We regress observed area burned onto observed meteorological fields and fire indices from the Canadian Fire Weather Index system and find that May-October mean temperature and fuel moisture explain 24-57% of the variance in annual area burned in this region. Applying meteorological fields calculated by a general circulation model (GCM) to our regression model, we show that increases in temperature cause annual mean area burned in the western United States to increase by 54% by the 2050s relative to the present day. Changes in area burned are ecosystem dependent, with the forests of the Pacific Northwest and Rocky Mountains experiencing the greatest increases of 78 and 175%, respectively. Increased area burned results in near doubling of wildfire carbonaceous aerosol emissions by midcentury. Using a chemical transport model driven by meteorology from the same GCM, we calculate that climate change will increase summertime organic carbon (OC) aerosol concentrations over the western United States by 40% and elemental carbon (EC) concentrations by 20% from 2000 to 2050. Most of this increase (75% for OC and 95% for EC) is caused by larger wildfire emissions with the rest caused by changes in meteorology and for OC by increased monoterpene emissions in a warmer climate. Such an increase in carbonaceous aerosol would have important consequences for western U.S. air quality and visibility.