Arctic September Sea Ice

This figure illustrates the extent to which Arctic sea ice is melting faster than projected by computer models. The dotted line represents the average rate of melting indicated by computer models, with the blue area indicating the spread among the different models (shown as plus/minus one standard deviation). The red line shows the actual rate of Arctic ice loss based on observations. The observations have been particularly accurate since 1979 because of new satellite technology. (Illustration by Steve Deyo, ©UCAR, based on research by NSIDC and NCAR. News media terms of use*)

The above figure is taken from a recent news release written by Marika Holland of the National Center for Atmospheric Research (NCAR). Here is the first paragraph:


BOULDER—Arctic sea ice is melting at a significantly faster rate than projected by even the most advanced computer models, a new study concludes. The research, by scientists at the National Center for Atmospheric Research (NCAR) and the University of Colorado’s National Snow and Ice Data Center (NSIDC), shows that the Arctic’s ice cover is retreating more rapidly than estimated by any of the 18 computer models used by the Intergovernmental Panel on Climate Change (IPCC) in preparing its 2007 assessments.

The article is entitled:

Arctic Ice Retreating More Quickly Than Computer Models Project


and was published 1 May, 2007 by the
GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L09501, doi:10.1029/2007GL029703, 2007. Here is the abstract (if you want to read the whole piece you will need to buy it from NCAR):

Abstract

From 1953 to 2006, Arctic sea ice extent at the end of the melt season in September has declined sharply. All models participating in the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) show declining Arctic ice cover over this period. However, depending on the time window for analysis, none or very few individual model simulations show trends comparable to observations. If the multi-model ensemble mean time series provides a true representation of forced change by greenhouse gas (GHG) loading, 33–38% of the observed September trend from 1953–2006 is externally forced, growing to 47–57% from 1979–2006. Given evidence that as a group, the models underestimate the GHG response, the externally forced component may be larger. While both observed and modeled Antarctic winter trends are small, comparisons for summer are confounded by generally poor model performance.


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