Regional, seasonal, and historic Arctic temperature change (Invited Presentation)

Parsing historical temperature data by season, decade, and region shows changes of several degrees and large spatial teleconnectivity. It is this teleconnectivity which is important to Arctic change, yet makes the problem of assigning causality difficult because of the large response of the natural system to both internal and external forcing. We propose a conceptual model based on three interrelated elements: 1) lower tropospheric/sea-ice/oceanographic interdecadal variability centered on the North Atlantic and central Arctic in winter, with strong North Atlantic Oscillation (NAO) influence; 2) subarctic lower stratospheric variability which includes a strengthening and northward shift of the polar vortex and persistence into spring in its positive mode, associated with the Arctic Oscillation (AO) or Northern Annular Mode (NAM). This mode is particularly important because of its contribution to persistent hemispheric multidecadal changes; 3) decoupling of the lower Arctic troposphere from the upper troposphere and stratosphere in early summer so that regional surface feedbacks are large. These feedbacks may amplify the Arctic response in ways that are yet to be fully demonstrated.

Time/longitude plots of temperature anomalies for different months based on 33 historical weather stations and proxy data illustrate these features. Scandinavia and western Siberia had warm temperatures in the winters in the 1930s and 1990s. In these years spring had warm temperature anomalies in NW North America(April). Summer patterns of temperature anomalies are similar to winter. The 1990s warming had a similar hemispheric dynamic response as the 1930s. In summary: a) there is evidence for polar amplification of anomalies, both positive and negative; b) the warming of the 1930s is not necessarily part of a Low-Frequency Oscillation (LFO), as the key feature of the 19th century is the very large temperature rise after the Little Ice Age; c) the response of the Arctic over the previous two centuries probably includes hemispheric effects from aerosols, CO2, and ozone acting as forcings to atmospheric dynamics through the NAM and regional Arctic feedbacks through vegetation and sea-ice cover.