Rectified multiyear warming in high latitudes by interannually varying biomass burning emissions in CESM2 Large Ensemble simulations

A merged biomass burning aerosol (BBA) emission dataset of satellite observations with fire proxies and fire models has been used in the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations. Although this utilizes best estimates of fire emissions based on available observations, it results in inconsistency in interannual variability of BBA forcing in CMIP6 between the period of satellite-based fire emissions (1997-2014) and the periods before and after. Using the Community Earth System Model version 2 Large Ensemble (CESM2-LE) simulations, we identify rectified multiyear mean climate responses to interannually varying BBA emissions. The comparison of 50 ensemble members forced by high BBA variability with 50 members by low BBA variability over a limited time domain provides a unique opportunity to identify a forced climate response to interannual fluctuations of fire emissions with high fidelity. While mean aerosol emissions are nearly conserved between the two sets of ensembles, there is detectable warming in northern high latitudes with regionally distinct seasonal changes in response to variable emissions. We find that the multiyear warming occurs in concert with a net loss of soil ice and moisture in addition to a loss of Arctic sea ice. Our results suggest that the magnitude of interannual variability of aerosol emissions can act as climate forcing over multiple years through nonlinear interactions with the cryosphere and soil processes.