Item

Abstract

[1] High-precision, multispecies measurements of flask air samples since 1992 from CSIRO's global sampling network reveal strong correlation among interannual growth rate variations of CO₂ and its delta(13)C, H-2,CH₄, and CO. We show that a major fraction of the variability is consistent with two emission pulses coinciding with large biomass burning events in 1994/1995 and 1997/1998 in tropical and boreal regions, and observations of unusually high levels of combustion products in the overlying troposphere at these times. Implied pulse strengths and multispecies emission ratios are not consistent with any other single process, but do not exclude possible contributions from covarying processes that are linked through climatic forcing. Comparison of CO₂ with its delta(13)C indicates that most of the CO₂ variation is from terrestrial exchange, but does not distinguish forcing by biomass burning from imbalance in photosynthesis/respiration of terrestrial ecosystems. Partitioning of terrestrial CO₂ fluxes is constrained by H-2,CH₄, and CO, all of which are products of biomass burning but which have no direct link to net respiration of CO₂. While CO is a strong indicator of biomass burning, its short lifetime prevents it from usefully constraining the magnitude of CO₂ emissions. If the H-2 and CH₄ variations were dominated by biomass burning, they would imply associated carbon emissions in excess of mean annual levels of other years, of 0.6-3.5 and 0.8-3.7 Pg C for 1994/1995 and 1997/1998, respectively. The large range in emission estimates mainly reflects uncertainty in H-2/CO₂ and CH₄/CO₂ emission ratios of fires in these years.