The Arctic is a region of extremes, and Arctic climate is changing – across atmosphere, ocean, sea ice and terrestrial systems - at a much more rapid pace than at lower latitudes. While these changes appear extreme compared to the recent past, the lack of long-term scientific observations makes it difficult to know if current and future Arctic changes are beyond the bounds of 20^th century Arctic climate, or if they represent a “New Arctic” state. Polar scientists at NCAR used the CESM Large Ensemble simulations to show how the Arctic is transitioning from a dominantly frozen state, and to quantify the nature and timing of an emerging new Arctic climate in sea ice, air temperatures and precipitation phase (rain vs. snow). Their results suggest that Arctic sea ice conditions are already statistically different from the beginning of the satellite era (1980s) and that under the “business as usual” CO₂ emissions scenario (RCP8.5), Arctic air temperatures and precipitation phase changes will emerge as statistically new in the early to mid 21^st Century (temperatures) and late 21^st Century (precipitation phase).

Figure: Histograms of the annual daily minimum (top) and maximum (bottom) Arctic Sea Ice Extent from the Large Ensemble (LE) for the early 20^th Century (1920-1929; blue) and later decades (red). First (1979-1986) and last (2008-2017) decadal means for the National Snow and Ice Data Center (NSIDC) SSMI observations are shown in dashed/solid lines respectively, with observed range shown in light grey for reference. Sea ice concentrations within SIC 15% contours for smallest (middle left; 2017) and largest (middle right; 27, 2013) SIE minimums during 2010-2019.

Reference

• Landrum, L. and M. H. Holland. The emergence of a New Arctic: when extremes become routine, submitted, Nature Climate Change, October 2019.