Biomass burning aerosol (BBA) emissions in the Coupled Model Intercomparison Project Phase 6 (CMIP6) historical forcing fields have enhanced temporal variability during the years 1997–2014 when they were estimated from satellite. The variability drives elevated warming relative to the pre-satellite period that is stored in the ocean and lasts into the late 21st Century, complicating assessments of climate change.
Ocean temperature and sea ice volume anomalies occur during periods of high BBA variability and subsequently persist over multiple decades. In the North Atlantic, surface warming is efficiently compensated for by decreased northward oceanic heat transport due to a slowdown of the Atlantic Meridional Overturning Circulation. In the North Pacific, surface warming is compensated for by an anomalous cross-equatorial cell (CEC) that reduces northward oceanic heat transport. The heat that converges in the South Pacific through the anomalous CEC is shunted into the subsurface and contributes to the formation of long-lasting ocean temperature anomalies.
Our analysis reveals the adverse impact in CESM2 of inconsistencies in climate-forcing datasets used in CMIP6 prescribed biomass burning emissions. The documented characteristics of this response provide insight into the sensitivity of climate to those datasets, their relevant mechanisms, and the structure of the response that needs to be accounted for in interpreting CESM2 projections of climate change, with potentially similar responses in other CMIP6-class models.