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 evaporative cooling to cause ice to regenerate. Those interested in the dynamics of Arctic sea ice can read numerous posts here. This post provides a look at mid August from 2007 to yesterday 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 melting season in August up to yesterday shows 2020 below average but appearing to consolidate in the recent days.
Both MASIE and SII show 2020 ice extents below average and other years beginning August and matching 2019 by mid month. In contrast 2007 melted slowly than other years reaching average later in August before dropping at the end. 2012 was an average year until the 2012 Great Cyclone, whose effects started after day 130 precipitating a drop of 1.7M km2 of ice in just two weeks. And as we know, 2012 went to record the lowest September in the record.
The table for day 228 shows how the ice is distributed across the various seas comprising the Arctic Ocean.
|Region||2020228||Day 228 Average||2020-Ave.||2007228||2020-2007|
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.
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.
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 below shows the second week in September over the last 11 years. 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 5 years compared to the 12 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.
via Science Matters
August 16, 2020 at 12:41PM