Optimal large-scale wind patterns favoring strong sea ice melting and ice-albedo feedback in the absence of anthropogenic forcing

Abstract:

Arctic sea ice has declined rapidly over the past 40 years, driven by a combination of increasing greenhouse gas emissions and internal variability. Several studies have attempted to separate the contributions of these drivers, placing the role of internal variability in recent sea ice decline between 30-50%. However, uncertainties remain regarding the representation of key high latitude processes and reconciling model simulations with observations. To address this, we constrain atmospheric circulation by nudging mid- to upper tropospheric Arctic (70-90N) winds (U,V) within the Community Earth System Model (CESM) to those from reanalysis, repeating each reanalysis year for 10 model years using fixed greenhouse gas concentrations and initializing from the same conditions. Composites show the strongest sea ice loss years are associated with anticyclonic circulation favoring downwelling longwave radiation and shortwave absorption. Successive years of relatively strong wind-driven melting also enhance declining trends in Arctic sea ice through the ice-albedo feedback. In the case of strong melting, sea ice returns close to the initial state when wind forcing is removed but does not fully reach its initial coverage until decades later due to heat stored in the ocean. These strong contributions of wind patterns to short- and long-term changes in Arctic climate make understanding these effects vital to improving forecasts and future projections of Arctic sea ice.