Julienne Stroeve from NSIDC asked me to post the figure below in reference to the discussion about future ice-free Arctic summers.
Some notes on the graph:
Model fields come from the models used in the IPCC 2007 report, using the observed record of GHGs from 1900 to 2000, and the “business as usual” scenario afterwards. For models with more than one ensemble member, the ensemble members have been averaged for that model. Observations come from a combination of satellite data, aircraft and ship observations.
The graph makes two important points:1) the models are in qualitative agreement with the observations that the September ice cover has been declining from 1953-2010. This is despite the fact that each model would be in their own phase of natural variability and could therefore be showing increases or decreases. This suggests, that in the models, the forcing by GHG contributes to the decline.2) the observations are outpacing the models in terms of the decline in the Arctic summer ice cover.
Thanks Julienne!