Something Odd About Regional Arctic Sea Ice

There is something strange about the Arctic sea ice data posted at Cryosphere Today.

If I sum up each individual sea’s contribution (plots at the bottom of this post), the totals do no agree with the overall Northern Hemisphere values.

This is a list of anomaly and absolute values in millions sq km, region by region for Sep 10, 2007; March 01, 2008 and Sep 09, 2008:

(Approximated values obtained with Plot Digitizer. I have asked Chapman for the actual figures…if I get them, I’ll change the post accordingly)

Region,Anomaly Sep 07,Anomaly Mar 08,Anomaly Sep 08,Absolute Sep 07,Absolute Mar 08,Absolute Sep 08,Mean Sep 07,Mean Mar 08,Mean Sep 08
Arctic Basin,-0.97,0.07,-0.75,2.37,4.2,2.59,3.34,4.13,3.34
Hudson Bay,-0.02,-0.05,-0.02,0,1.22,0,0.02,1.27,0.02
St Lawrence,0,0,0,0,0.19,0,0,0.19,0
Baffin/Newfoundland,-0.03,0.16,-0.02,0,1.33,0.01,0.03,1.17,0.03
Greenland,0.06,-0.06,-0.04,0.17,0.52,0.07,0.11,0.58,0.11
Barents,-0.04,-0.24,-0.04,0,0.41,0,0.04,0.65,0.04
Kara,-0.1,0.02,-0.09,0.04,0.86,0.05,0.14,0.84,0.14
Laptev,-0.07,0.02,-0.04,0.1,0.7,0.13,0.17,0.68,0.17
East Siberian,-0.31,0.01,-0.31,0.01,0.9,0.01,0.32,0.89,0.32
Chukchi,-0.08,0.02,-0.08,0,0.59,0,0.08,0.57,0.08
Bering,0,0.16,0,0,0.7,0,0,0.54,0
Okhotsk,0,-0.3,0,0,0.7,0,0,1,0
Beaufort,-0.13,0.02,-0.17,0.04,0.52,0,0.17,0.5,0.17
Canadian Archipelago,-0.13,0,-0.1,0.11,0.6,0.14,0.24,0.6,0.24
Totals,-1.82,-0.17,-1.66,2.84,13.44,3,4.66,13.61,4.66

Northern Hemisphere,-2.05,-0.48,-1.92,2.94,13.85,3.17,4.99,14.33,5.09

difference,-0.23,-0.31,-0.26,0.1,0.41,0.17,0.33,0.72,0.43

(The “Mean” columns reconstruct the 1979-2000 mean by subtracting the anomaly from the absolute measured ice cover)

You can see that my digitization appears to consistently underestimate the anomalies, and overestimate the absolute measured ice cover. The result is that there is for example a huge 720,000sq km difference between the total of all 1979-2000 March means, and the value reported for the Northern Hemisphere on Cryosphere Today.

It would be nice to know if anybody else has attempted this, and/or has the actual values rather than the graphs.

NOTE ADDED 11 SEP: Unfortunately the graphs below do not use the same scale, so visual inspection can be misleading