The animation above shows Arctic ice extents from Sept. 1 to 16, 2020. On the left are the Russian shelf seas already ice-free, and the Central Arctic retreating as well. Bottom left is Beaufort Sea losing ice. In the last week CAA in the center starts refreezing, and just above it Baffin Bay starts to add ice back. At the top right Greenland Sea starts to refreeze.
Prof. Peter Wadhams made multiple predictions of an ice-free Arctic (extent as low as 1M km2), most recently to happen in 2015. Thus was born the metric: 1 Wadham = 1M km2 Arctic ice extent. The details are provided on 2020 minimum below. Though there could be a dip lower in the next few days, the record shows a daily minimum of 3.7M km2 on September 11 (MASIE) and September 13 (SII). While BCE (Beaufort, Chukchi, East Siberian seas) may lose more ice, gains have appeared on the Canadian side: CAA, Baffin Bay and Greenland Sea. So 3.7 Wadhams may well hold up as the daily low this year. Note that day 260, September 16, 2020, is the date for the lowest annual extent averaged over the last 13-years.
The discussion later on refers to the September monthly average extent serving as the usual climate metric. That stands presently at 3.9M km2 for MASIE and 3.8M km2 for SII, with both expected to rise slightly by month end as ice extent typically recovers.
The melting season this year showed ice extents briefly near the 13-year average on day 241, then dropping rapidly to go below all other years except 2012. That year was exceptional due to the 2012 Great Arctic August Cyclone that pushed drift around producing a new record minimum. The anomaly this year was the high pressure ridge persisting over Siberia producing an extremely hot summer there. This resulted in early melting of the Russian shelf seas along with bordering parts of the Central Arctic.
As discussed below, the daily minimum on average occurs on day 260, but a given year may be earlier or later. The 2020 extent began to flatten from day 248 onward in SII (orange) while MASIE showed stabilizing from day 252 with an upward bump in recent days. Both lines are drawing near 2019 and 2007 while departing from 2012. The table below shows the distribution of ice in the various regions of the Arctic Ocean.
|Region||2020260||Day 260 Average||2020-Ave.||2012260||2020-2012|
The extent numbers show that this year’s melt is dominated by the surprisingly hot Siberian summer, leading to major deficits in all the Eurasian shelf seas–East Siberian, Laptev, Kara. As well, the bordering parts of the Central Arctic show a sizeable deficit to average. The main surpluses to average and to 2012 are Beaufort, Greenland Sea and CAA.
It is also the case that many regions have already registered their 2020 minimums. And as discussed below, the marginal basins have little ice left to lose.
Background from Previous Post Outlook for Arctic Ice Minimum
The annual competition between ice and water in the Arctic ocean is approaching the maximum for water, which typically occurs mid September. After that, diminishing energy from the slowly setting sun allows oceanic cooling causing ice to regenerate. Those interested in the dynamics of Arctic sea ice can read numerous posts here. The image at the top provides a look at mid August from 2007 to 2020 as a context for anticipating this year’s annual minimum. Note that for climate purposes the annual minimum is measured by the September monthly average ice extent, since the daily extents vary and will go briefly lower on or about day 260.
The Bigger Picture
We are close to the annual Arctic ice extent minimum, which typically occurs on or about day 260 (mid September). Some take any year’s slightly lower minimum as proof that Arctic ice is dying, but the image above shows the Arctic heart is beating clear and strong.
Over this decade, the Arctic ice minimum has not declined, but since 2007 looks like fluctuations around a plateau. By mid-September, all the peripheral seas have turned to water, and the residual ice shows up in a few places. The table below indicates where we can expect to find ice this September. Numbers are area units of Mkm2 (millions of square kilometers).
|Day 260||13 year|
|Central Arctic Sea||2.67||3.16||2.64||2.98||2.93||2.92||3.07||2.91||2.97||2.93|
|Greenland & CAA||0.56||0.41||0.41||0.55||0.46||0.45||0.52||0.41||0.36||0.46|
The table includes three early years of note along with the last 6 years compared to the 13 year average for five contiguous arctic regions. BCE (Beaufort, Chukchi and East Siberian) on the Asian side are quite variable as the largest source of ice other than the Central Arctic itself. Greenland Sea and CAA (Canadian Arctic Archipelago) together hold almost 0.5M km2 of ice at annual minimum, fairly consistently. LKB are the European seas of Laptev, Kara and Barents, a smaller source of ice, but a difference maker some years, as Laptev was in 2016. Baffin and Hudson Bays are inconsequential as of day 260.
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 this context, it is foolhardy to project any summer minimum forward to proclaim the end of Arctic ice.
Resources: Climate Compilation II Arctic Sea Ice
via Science Matters
September 17, 2020 at 01:54PM