Is There a Forced Signal in the Recent Reduced Rate of Arctic Sea Ice Loss?

Abstract:

Over the period of satellite observations, the Arctic sea ice cover has been characterized by a strong downward trend, which has been accelerating since the start of the 21^st century (Serreze and Stroeve, 2015). Since 2012, Arctic sea ice loss has continued but at a slower rate than in the early 2000s. In fact, the largest negative 20-year linear trend in September sea ice extent and area is seen for trend end year in 2012. We find that several models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) also show this reduction in September sea ice loss trends for trend end years around 2010, with neutral or even slightly positive values for trend end years between 2020 and 2030. In models this behavior is not due to internal variability, suggestive of a forced response to a non-CO₂ climate forcing. So far, we have been able to rule out a few possible forcings in one CMIP6 model, the Community Earth System Model version 2 (CESM2): near-term climate forcers (NTCFs: methane, tropospheric ozone and aerosols) and their precursors as well as anthropogenic and biomass burning secondary organic aerosol emissions (DeRepentigny et al., 2020). A thorough assessment of the CMIP6 forcing and the climate response to that forcing is currently being carried out to identify the driver of this change in sea ice loss trends. Comparisons to observed changes will elucidate whether similar factors may have contributed to the observed evolution of Arctic sea ice loss. The results from this analysis will provide insights into the potential for a forced contribution to the recent reduced rate of observed Arctic sea ice loss.