Tropical Pacific Variability and its Influence on Twenty-First Century Arctic Sea Ice Loss
In the first, internal variability in twenty-first-century summer Arctic sea ice loss and its relationship to the large-scale atmospheric circulation is investigated in a 39-member Community Climate System Model, version 3 (CCSM3) ensemble for the period 2000–2061. Each member is subject to an identical greenhouse gas emissions scenario and differs only in the atmospheric model component's initial condition. A surprisingly large factor of three range in the multi-decadal trends of Arctic sea ice loss results, which can only be attributed to internal variability. Higher rates of summer Arctic sea ice loss in CCSM3 are associated with enhanced transpolar drift and Fram Strait ice export driven by surface wind and sea level pressure patterns. Outside the Arctic, an atmospheric Rossby wave train over the Pacific sector is associated with internal ice loss variability. The structure of the atmospheric teleconnection patterns in CCSM3 suggests that the tropical Pacific modulates Arctic sea ice loss via the aforementioned Rossby wave train. The second study generally corroborates results in the first by documenting qualitatively similar relationships in a newer model version and across a Coupled Model Intercomparison Project (CMIP) ensemble. Hints of a similar tropical Pacific-Arctic sea ice variability relationship are also present in various reanalyses at the interannual time scale.