Arctic ice extent has been fairly stable since 2007 and is now 500.000 square kilometres (193,000 sq miles) higher than 10 years ago.
September daily extents are now fully reported and the 2017 September monthly results can be compared with years of the previous decade. MASIE showed 2017 exceeded 4.8M km2 and SII was close behind, also reaching 4.8M for the month. The 11 year linear trend is more upward for MASIE, mainly due to 2008 and 2009 reported higher in SII. In either case, one can easily see the Arctic ice extents since 2007 have not declined and are now 500k km2 higher.
In August, 4.5M km2 was the median estimate of the September monthly average extent from the SIPN (Sea Ice Prediction Network) who use the reports from SII (Sea Ice Index), the NASA team satellite product from passive microwave sensors.
The graph below shows September comparisons through day 273 (Sept. 30).Note that starting day 26 2016 had begun its remarkable recovery, and is now well above the 10 year average, nearly matching 2017. Meanwhile 2007 is 1.1M km2 behind and the Great Arctic Cyclone year of 2012 is 1.4M km2 less than 2017. Note also that SII is currently matching MASIE.
The narrative from activist ice watchers is along these lines: 2017 minimum is not especially low, but it is very thin. “The Arctic is on thin ice.” They are basing that notion on PIOMAS, a model-based estimate of ice volumes, combining extents with estimated thickness. That technology is not mature, and in any case refers to the satellite era baseline, which began in 1979.
The formation of ice this year does not appear thin, since it is concentrated in the central Arctic. For example, Consider how Laptev and East Siberian seas together added 180k km2 in the just the last ten days:
Earlier observations showed that Arctic ice extents were low in the 1940s, grew thereafter up to a peak in 1977, before declining. That decline was gentle until 1994 which started a decade of multi-year ice loss through the Fram Strait. There was also a major earthquake under the north pole in that period. In any case, the effects and the decline ceased in 2007, 30 years after the previous peak. Now we have a plateau in ice extents, which could be the precursor of a growing phase of the quasi-60 year Arctic ice oscillation.
For context, note that the average maximum has been 15M, so on average the extent shrinks to 30% of the March high before growing back the following winter. In 2017 about 33% of the March maximum was retained, so the melt season losses were considerably less than in the past.