And so the Arctic refreeze that began on September 19th, after a summer of devastating melt, continues apace. Temperatures are falling throughout the Arctic as the sun dips lower and lower on the horizon, beginning a phase that will eventually result in the total darkness of winter. As you can see on the map above, snowfall is starting to blanket land masses in the region. But an ominously large and dark open expanse of water remains.
Extent, Area Still Close to or Below Previous Records For End of Summer
It is October 5th, 16 days after refreeze began and 20 days after a typical melt season’s end. Yet some measures are still showing Arctic sea ice below past record lows set in 2007. NSIDC and IMS are still showing ice extent values just below the 2007 level. With that record breached on August 25th of this year, we have experienced 41 days, or 11% of the entire year, with sea ice extent values below the previous record low set in 2007.
What this means is that large, dark areas of ocean are having a longer time to absorb heat from sunlight and remain warm for longer periods. What it also means is that a greater degree of endothermic cooling is needed to freeze a much larger expanse of ocean. The result is that much of this cooling work goes to refreeze and less and less goes to thickening the ice. This combination of getting ever further behind the refreeze curve and having to refreeze in a warming ocean sets up the Arctic for even deeper melt in the years following.
All measures show today is a record low for this date in history. Sea ice area is 3.1 million square kilometers below the 1980 value and sea ice extent is currently 3.5 million square kilometers below the 1980 value for today (NSIDC). Sea ice extent is also about 800,000 square kilometers below the record low set in 2007 for today’s date. Sea ice area is about 480,000 square kilometers below the 2007 value for today’s date. These values are roughly equal to the minimum departure seen at melt season’s end. So, though refreeze has begun, the gap, for the moment, remains. However, as the refreeze season progresses, all measures except volume should appear to show some recovery as the ice spreads out with seasonal cooling. We will have to see how much the severe blow that occurred this summer affects overall winter sea ice area, extent, and volume.
New Volume Measure Shows 700 Cubic Kilometers Lost This Year
In my summary post for the epic melt that occurred in 2012 and its implications for melt in the years to follow, I included the final volume measurements for the melt season’s end in September. But it is also worth providing a summary for you here.
Overall, volume fell to 3,300 cubic kilometers, 700 cubic kilometers lower than the record low of 4,000 cubic kilometers set last year. Average yearly volume losses since 2007 are such that, should they continue at the current rate, the Arctic experiences an ice-free state at the end of summer by 2018. Exponential volume loss trends still point toward a potential ice-free state as early as 2015.
These two dates are critical in determining the Arctic’s response both to current melt rates and feedbacks. Should they materialize, we will know that all ice in the Arctic is headed for a rapid melt far sooner than predicted by the major science bodies. And this particular case has very severe implications for Greenland and for world sea level rise.
And a Few Words on Arctic Methane
Arctic methane concentrations will continue to climb through the fall and into early winter. We shall keep an eye on these readings since, as satellite data shows, their concentrations have been growing over the years and because they are one of the number of amplifying feedbacks occurring in the Arctic environment. The size of past pulses and their relative rate of growth is some cause for watchfulness, so we will do our best to track this year’s methane emission peak given the limited tools available.
The most recent methane data for Barrow Alaska is posted below (updated on September 29th, 2012). Note the three outliers at the upper right corner of the graph that caused some concern earlier in September but were confirmed to be from a likely human source. We will also be posting satellite images and comparisons from the University of Maryland as they become available.