Variability of Biomass Burning Emissions in CMIP6 Forcing only Minimally Impacts Precipitation in the CESM2-LENS

Over 1997-2014, the CMIP6 historical experiments were forced with a period of discontinuously high variability in biomass burning emissions. Prior studies have shown that this dramatic increase in variability increases net surface shortwave radiation, particularly from 40-70N, and impacts the evolution of Arctic sea ice. Here, we use the CESM2 Large Ensemble to show that this increased variability in biomass burning emissions also leads to an average sea surface temperature (SST) increase of up to 0.2 K from 1997-2014. Despite this significant increase in SSTs, we find that there is only a small increase to precipitation: mean precipitation from 40-70N increases by 0.3%, or 0.01 mm day-1. Most regional changes in the annual mean and extreme precipitation are not statistically significant. This small increase in precipitation is driven by increased local evaporation and stronger moisture convergence. However, it is also buffered by increased ocean heat uptake and heat storage, which slows evaporation over the ocean. Increased variability in biomass burning emissions also impacts tropical precipitation: the Northern Hemisphere Hadley cell weakens, while the Southern Hemisphere Hadley cell strengthens. These findings suggest that variability in biomass burning emissions, not just the total amount of such emissions, may impact precipitation trends.