September Arctic sea ice extent based on 89 ensemble members from 36 CMIP5 models under the RCP8.5 (high) emissions scenario. Each thin colored line represents one ensemble member from the model. The thick yellow line is the arithmetic mean of all ensemble members and the blue line is their median value. The thick black line represents observations based on adjusted HadleyISST_ice analysis for the period 1953-1978, and NSIDC from 1979-2012. Observation data were provided by Meier, NSIDC. The horizontal black dashed line marks the 1.0 M km2 value, which indicates nearly sea ice free summer Arctic. Graphic: Overland and Wang, 2012

ABSTRACT: The observed rapid loss of thick, multi-year sea ice over the last seven years and September 2012 Arctic sea ice extent reduction of 49% relative to the 1979-2000 climatology are inconsistent with projections of a nearly sea ice free summer Arctic from model estimates of 2070 and beyond made just a few years ago. Three recent approaches to predictions in the scientific literature are: 1) extrapolation of sea ice volume data, 2) assuming several more rapid loss events such as 2007 and 2012, and 3) climate model projections. Time horizons for a nearly sea ice free summer for these three approaches are roughly 2020 or earlier, 2030 ± 10 yrs, and 2040 or later. Loss estimates from models are based on a subset of the most rapid ensemble members. It is not possible to clearly choose one approach over another as this depends on the relative weights given to data versus models. Observations and citations support the conclusion that most Global Climate Models results in the CMIP5 archive are too conservative in their sea ice projections. Recent data and expert opinion should be considered in addition to model results to advance the very likely timing for future sea ice loss to the first half of the 21st century, with a possibility of major loss within a decade or two.

When will the summer arctic be nearly sea ice free? [pdf]

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