A slowing in sea ice area and extent melt during May has born out in the PIOMAS volume numbers. According to the most recent PIOMAS update, pace of Arctic sea ice volume melt remained about level during mid-to-late May. In past record melt years, 2011 and 2012 volume melt picked up by the end of May.
2013’s end May melt, however, was more gradual:
(Image source: PIOMAS)
As a result, sea ice volume has edged away from record low territory and is currently the third lowest in the measure. It’s a number still quite close to record lows, sitting about 900 cubic kilometers above 2012 values. But closer yet is 2010, the 4th lowest year, which was about 200 cubic kilometers above 2013 by end of May.
Overall, Arctic sea ice volume is a bit more substantial, but still low enough to be worthy of concern. The reason is that, as noted before, the disposition of Arctic sea ice this year is, overall, thin and spread out. PIOMAS shows overall ice thickness just slightly above record low values. While Arctic Ice Blog Neven’s crude ice thickness calculator that simply divides PIOMAS volume by Cryosphere Today area shows ice currently at its thinnest on record:
(Image source: Neven)
It is also worth pointing out that Greenland and the Central Arctic above the 80th parallel has been somewhat cooler than average this May, despite large regions of substantial warming present in other areas. Whether this trend persists and whether it has an impact on melt for 2013, will be more readily apparent as June progresses.
Emergence of negative feedbacks?
A prolonged slow-down in sea ice volume melt would also begin to beg the question: have negative feedbacks started to emerge in the Arctic? Large influxes of fresh water from Greenland have been flushing into the Arctic since the early 2000s. So one wonders if such high volumes of cold, fresh water could be involved in rejuvenating the Cold Arctic Halocline (CAH) layer while at the same time pumping colder water into the North Atlantic.
This layer of cold water is a key protector of the Arctic ice pack. Over the past few decades, the CAH has been undergoing dramatic retreat. Its retreat is a primary reason why the sea ice is so vulnerable to impacts from a warming ocean beneath. (A number of scientific papers have been written on this subject. The Response to Climate Change of the Cold Arctic Halocline, Shielding Sea Ice from the Warm Deep Water Below is just one example.)
In the Antarctic, scientific research has shown that glacial melt on the Antarctic continent has provided a cold layer of protective water which, in turn, has made the sea ice more resilient there. So if 2013 melt does slow and we get a trend of slower sea ice melt years to follow, it will be worth investigating if such a negative feedback is currently active in the Arctic.
Evidence of Negative Feedbacks in Paloeclimate
An increasing pace of northern hemisphere ice sheet melt has also been implicated in past climate swings. The Younger Dryas period occurring about 12,000 years ago was initiated by the breaking of an ice damn in the Laurentide ice sheet which covered a large portion of North America. This ice damn collapse flooded cold water into the North Atlantic which initiated major swings in climate — setting off a period of colder temperatures that lasted for about 1,000 years.
Geological observations of such a large infusion of cold, fresh water provides an example of how large volumes of melt water can act as a negative feedback and cool the climate. Present day Greenland melt is substantial, averaging about 500 cubic kilometers per year, though certainly not as substantial as what occurred during the Younger Dryas. Nonetheless, Greenland and Canadian Arctic Archipelago glacial melt is likely to have an impact on both sea ice and climate as melt rates increase.
This will be something worth looking at if volume melt continues to slow and cooler conditions begin to persistently crop up in the Arctic. At some point, human greenhouse gas forcing is likely to achieve such an event. When this happens, Arctic temperatures are expected to cool even as warming increases in the lower latitudes. The weather consequences for such an event are quite dramatic (a subject worth exploring in another blog).
All that said, the above is purely speculative and we would have to see a more consistent slow-down in volume melt as well as a regime of cooler Arctic temperatures to validate such an occurrence.
Not out of the Woods Yet
So it is worth emphasizing that we are not out of the woods yet. One month of slower than blindingly fast volume melt in the context of some of the thinnest ice on record does not a trend make.
More ice volume remains in areas outside the Central Arctic Basin and so will be more vulnerable to mid-to-late-season melt. In contrast, Central Arctic ice is much thinner than usual, also making it vulnerable. So volume numbers will be more telling once we start getting substantial melt in Hudson Bay, Baffin Bay, and the Kara Seas. Speculation for a major June melt, for various reasons, is running particularly high (An interesting and well-thought-out take is that of Chris Reynolds over at Dosbat.).
This fragile state makes end of June PIOMAS numbers an important indicator. If temperatures are cool, the edge ice stays more resilient, the central ice is able to hold together under the pounding of our Persistent Arctic Cyclone (PAC) of 2013, and the pace of overall melt remains slower as volume numbers remain somewhat higher by end of June, then it becomes a bit less likely we will see another record year in 2013. Were such an event to occur, we’d have to revise our end-of-year melt risk estimate downward.
We are still in record low territory. June is a volatile month. And we have the PAC of 2013 as well as the potential emergence of warmer waters from the depths to contend with. So June is likely to be a very, very interesting month.
robertscribbler 
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