It’s been a pretty rough Summer for Arctic sea ice. Rougher than one would expect when considering how rapidly Greenland is melting and given that the Gulf Stream appears to be slowing down.
Increased rates of Greenland melt, increased fresh water outflow from rivers into the Arctic Ocean, and increases in ice berg calving have provided more fresh water to the Arctic Ocean (which would tend to cool the ocean surface) and weakened the south-to-north heat transfer of the Gulf Stream. Under such conditions, we’d tend to expect more than a little rebound in Arctic sea ice coverage. What we instead saw was a brief bump in the sea ice area, extent and volume measures during 2013 and 2014.
As of September 2nd, less than two weeks shy of traditional melt season end, sea ice extent in the JAXA measure had hit second lowest on record (please also see Neven’s most recent comprehensive sea ice report for his take on near end season ice states).
(Japan’s sea ice monitoring facility finds Arctic extent values at second lowest on record for September 2, 2015. Image source: JAXA.)
It’s a trend well below the 2014 pseudo-recovery year. One that is now tracking just beyond the previously record-smashing 2007 trend line. The measure of 4.346 million square kilometers is about 60,000 square kilometers below 2007. And though still quite a bit higher than 2012, it’s a swing that pushes toward a somewhat unsettling reassertion of the long-term melt trend. A trend that since the 1970s has reduced late season sea ice coverage by nearly half.
Other measures, though slightly less pronounced than the JAXA monitor, also show significant departures below the pseudo-recovery years 2014 and 2013. The NSIDC extent measure places the 2015 melt season as roughly tied with 2007 as second lowest on record and a 4.586 million square kilometer coverage. Meanwhile, sea ice area is tracking the 2010 melt line at 6th lowest on record for the date at 3.322 million square kilometers — a substantial 370,000 (approximate) square kilometers below 2014 — in the Cryosphere Today measure.
Conditions in Context — Preparation for Another Record-Breaker in 2016 and 2017?
Given recent science and observations showing increased rates of Greenland melt, increased fresh water flows into the Arctic Ocean, and a slowdown of the Gulf Stream, North Atlantic Overturning Circulation, and a related development of a cool pool between Greenland and England, we should probably assume that the Arctic is now involved in a climate change feedback tug of war. On the one hand you have rising atmospheric greenhouse gas levels in the Arctic due to a combination of human emissions and a growing carbon feedback response from permafrost and seabed stores. This heat-trapping atmospheric witch’s brew couples with loss of sea and land ice albedo to push for a continued rapid Arctic warming. On the other hand, you have fresh water outflows interrupting some of the south-to-north heat transfer in the North Atlantic and keeping a lid on some of the ocean heat in the High Arctic and near Greenland.
(A storm churns through the Laptev Sea on September 3, 2015, hurling 25-35 mph winds and 6-10 foot seas at the nearby ice. Trends show that 2015 is likely to be a year of ice losses, with end summer area and extent values in the range 2nd to 6th lowest on record. Image source: LANCE MODIS.)
Adding to this volatile mix is a potentially record-shattering El Nino which will, over the course of the next two years generate an ocean and atmospheric heat pulse that will probably maximize in the Arctic come 2017. Since 2015 is seeing returns to sea ice area and extent values in the range of 2010, 2011, 2008 and previous record low year 2007, there appears to be a preparation for the Arctic to challenge 2012 record low values over the 2016-2017 time period. And if sea ice does hit new record low values during that period of heightened risk we can also expect the whip-lash melt response from Greenland to grow even stronger.