Pre-industrial Southern Hemisphere biomass burning variability inferred from ice core carbon monoxide records

Abstract

Biomass burning plays an important role in climate-forcing and atmospheric chemistry. The drivers of fire activity over the past two centuries, however, are hotly debated and fuelled by poor constraints on the magnitude and trends of pre-industrial fire regimes. As a powerful tracer of biomass burning, reconstructions of paleo-atmospheric carbon monoxide (CO) can provide valuable information on the evolution of fire activity across the pre-industrial to industrial transition. Here too, however, significant disagreements between existing CO records currently allow for opposing fire histories. In this study, we reconstruct a continuous record of Antarctic ice core CO between 1822 and 1995 CE to overlap with direct atmospheric observations. Our record indicates that the Southern Hemisphere CO burden ([CO]) increased by 50% from a pre-industrial mixing ratio of ca. 35 ppb to ca. 53 ppb by 1995 CE but with a greater level of variability than allowed for by state-of-the-art chemistry-climate models, suggesting that historic CO dynamics have been not fully accounted for. Using a 6-troposphere box model, a 40-50% decrease in Southern Hemisphere biomass burning, coincident with unprecedented rates of early 20th century anthropogenic land-use change, is identified as a strong candidate for this mismatch.