Tropical Pacific Variability and its Influence on Twenty-First Century Arctic Sea Ice Loss
Abstract:Large declines in Arctic sea ice volume and summer sea ice extent are generally anticipated for the coming decades, based upon their trajectory in available observations and from a wide variety of greenhouse gas-forced model projections. Substantial uncertainty remains, however, regarding the magnitude of twenty-first century Arctic sea ice loss. Two studies are presented that document and explore the existence of an atmospheric teleconnection between the tropical Pacific and the Arctic on time scales ranging from the interannual to the multi-decadal.
In the first study, 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 is projected, 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, the internal variability in sea ice loss is associated with an atmospheric Rossby wave train concentrated over the Pacific sector. The structure of the atmospheric teleconnection pattern 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.