Influences of boreal fire emissions on Northern Hemisphere atmospheric carbon and carbon monoxide

Abstract

There were large interannual variations in burned area in the boreal region (ranging between 3.0 and 23.6 × 10 6 ha yr−1) for the period of 1992 and 1995–2003 which resulted in corresponding variations in total carbon and carbon monoxide emissions. We estimated a range of carbon emissions based on different assumptions on the depth of burning because of uncertainties associated with the burning of surface‐layer organic matter commonly found in boreal forest and peatlands, and average total carbon emissions were 106–209 Tg yr−1 and CO emissions were 33–77 Tg CO yr−1. Burning of ground‐layer organic matter contributed between 46 and 72% of all emissions in a given year. CO residuals calculated from surface mixing ratios in the high Northern Hemisphere (HNH) region were correlated to seasonal boreal fire emissions in 8 out of 10 years. On an interannual basis, variations in area burned explained 49% of the variations in HNH CO, while variations in boreal fire emissions explained 85%, supporting the hypotheses that variations in fuels and fire severity are important in estimating emissions. Average annual HNH CO increased by an average of 7.1 ppb yr−1 between 2000 and 2003 during a period when boreal fire emissions were 26 to 68 Tg CO−1 higher than during the early to mid‐1990s, indicating that recent increases in boreal fires are influencing atmospheric CO in the Northern Hemisphere.