Some might be interested to compare MASIE results with NOAA Sea Ice Index, since NOAA is a typical reference for Arctic Ice news. NOAA uses only passive microwave readings, while MASIE includes other sources, such as satellite images and field observations.
For comparison, MASIE shows about 700,000 Km2 more ice extent than NOAA both at maximum and minimum. This is usually explained by microwave sensors seeing melt water on top of ice the same as open water.
For the years 2007 to 2014 inclusive, each year MASIE shows higher maximums than NOAA, on average 5% higher. In each of those same years MASIE shows higher minimums than NOAA, on average 15% higher. The melt extent is more comparable: NOAA shows an average annual loss of 70.5 %, while MASIE shows an average loss of 67.5%.
Climatologists say the NIC estimates are “conservative.” By this they mean NIC’s priority is shipping safety, and so, when in doubt, under mixed ice and water conditions, ice charts show ice. NIC people do not make predictions about sea ice, they only report what is there, according to their multiple sources.
On the other hand, principals at both NASA and NOAA have said on the record that the Arctic will soon be ice-free, and it will be the fault of CO2. Could it be when in doubt, under mixed conditions, they report water in places where NIC shows ice? That would explain the discrepancies in estimates of ice extent
Note: NOAA has bureaucratic authority over NIC and advises against using NIC records for climate analysis. Last year, NIC results became available only on a rolling 30-day basis, so that estimates older than the current period are no longer available. Noticing this policy change, I began building a spreadsheet to capture the history for my own analysis. Since mid November, 2014, NIC ice extent reports have been unavailable at the MASIE webpage.
Update on April 2: NSIDC now says MASIE will be back after April.
Update November 2015: MASIE dataset is now available from January 1, 2006 to the present.