Arctic sea ice extent in 2007 (dark blue), 2012 (dashed dark green) and 2017 (light blue). The heavy grey line is the 1981 – 2010 median ice extent. Regions lying below the light grey shaded area are below the lowest 10% of measured values. This year has featured a lower extent than 2007 and 2012 thus far, but other years—2010, 2015 and 2016 (not shown)--have featured even less extent in early June. Graphic: NSIDC

By Bob Henson
9 June 2017

(Wunderground) – The Arctic Ocean’s coating of sea ice—now remarkably thin and sparse after a record-warm winter—could plummet by late summer to the lowest extent in 38-plus years of observations. Weather conditions over the next few weeks will determine just how much melting ultimately occurs. However, the ice is so depleted that even a melt season from here on that’s average by recent standards could leave the ice at a record-low extent.

Thus far, the 21st century has seen two grand dips in Arctic sea ice extent, in 2007 and in 2012. In both cases, the ice saw a modest but incomplete recovery, and the 38-year observation period can be easily split into “before” and “after”: each year after 2007 has seen a lower minimum than each year beforehand.

The sorry state of Arctic sea ice right now isn’t readily apparent if you look only at extent (the amount of ocean covered by at least 15% concentration of ice). On Wednesday, the National Snow and Ice Data Center reported that Arctic sea ice extent in May was the fourth lowest on record. That brought an end to the string of record-low monthly values set or tied in January, February, March, and April. Colder-than-usual weather at high latitudes helped keep the ice extent from shrinking in May as much as it typically does.

Sea ice is more than skin-deep, though. The total 3-D volume of Arctic sea ice is the least on record for this time of year in estimates from PIOMAS (the University of Washington’s Pan-Arctic Ice Ocean Modeling and Assimilation System). Since the ice’s horizontal extent isn’t quite at a record low, this implies that the average thickness is exceptionally small right now, as suggested by PIOMAS.

The fear among Arctic observers is that early-summer conditions could take advantage of that thin ice and produce a dramatically accelerated melt at some point in the next few weeks, perhaps leading to a “cliff” (a striking drop that shows up clearly on a graph of sea ice extent). […]

Jim Pettit (who goes by the handle Neapolitan at WU) shared similar concerns in an email on Wednesday: “With the current record-low volume coupled with the not-record-low extent, we can assume that the bulk of the ice is thinner than usual. Satellite images seem to bear this out; it appears that much of the ice has already cracked up, and that which is still together is nevertheless frangible and fractured, and not likely to last until mid-September. The next 100 days or so are going to be very interesting indeed.” [more]

Arctic Sea Ice Primed for Phenomenal Melt Season

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