Enhanced simulated early 21st century Arctic sea ice loss due to CMIP6 biomass burning emissions

The mechanisms underlying decadal variability in Arctic sea ice remain actively debated. Here, we ability in boreal biomass burning (BB) emissions strongly influences simulated Arctic sea ice on multidecadal time scales. In particular, we find that a strong acceleration in sea ice decline in the early 21st century in the Community Earth System Model version 2 (CESM2) is related to increased variability in prescribed BB emissions in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) through summertime aerosol-cloud interactions. Furthermore, we find that more than half of the reported improvement in sea ice sensitivity to CO2 emissions and global warming from CMIP5 to CMIP6 can be attributed to the increased BB variability, at least in the CESM. These results highlight a new kind of uncertainty that needs to be considered when incorporating new observational data into model forcing while also raising questions about the role of BB emissions on the observed Arctic sea ice loss.

Automated summary

This study finds that decadal variability in Arctic sea ice is strongly influenced by boreal biomass burning (BB) emissions, and the acceleration of sea ice decline can be attributed to increased variability in BB emissions through summertime aerosol-cloud interactions. Furthermore, it is discovered that more than half of the improvement in sea ice sensitivity to CO2 emissions and global warming from CMIP5 to CMIP6 can be attributed to increased variability in BB emissions, at least in the CESM model.