Update September 26: 2015 ice extent goes over 5M km2.
The daily ice extent minimums are behind us, and now the story is how fast is this year’s recovery of ice compared to last year.
In the MASIE estimates, the daily minimums were quite close in time: 2014 day 262 and 2015 day 260. NOAA showed 2015 minimum extent on day 251 with gains sufficient for NOAA to nearly synchronize with MASIE extent by day 262.
From last year’s MASIE records we know that ice recovered in 2014 at a rate of 41k km2 per day to the end of September, for a total addition of ice extent of 451k km2. NOAA showed a comparable gain in 2014 ice over the same period: 39k daily for a total gain of 429k km2.
As of day 268, Sept. 25, ice extent is recovering much faster this year than last, about twice the rate, and MASIE is again showing higher extent than NOAA.
First the daily situation:
September 25 day 268 results from MASIE. 2015 is back over 5M km2. Both years gain back considerable ice.
While 2014 gained 105k of ice, 2015 gained 64k recovering back up to 34% of the spring maximum..
2015 ice extent now trails 2014 by 6.4%, which is about 344k km2 difference.
Extent in BCE region is building ice now at 75% of last year, with Chukchi and East Siberian seas adding 47k. Most seas increased ice and most importantly, the Central Arctic is now 193k above its minimum 24 days ago.
The graph shows that a gap opened when 2015 ice dropped at the time of an Arctic cyclone late August. The differential of almost 1M km2 has now been cut to 350k km2. and closing. 2015 ice extent was lower than 5M km2 for only 27 days.
The first 25 days of September 2015 are in the books, so with 5 days to go this is an outlook on the melt season conclusion beyond the daily minimums.
For most of the season, 2015 Arctic sea ice extent was tracking 2014. In fact the July average extent was slightly higher than 2014. Then weather intervened in the last week of August. A large and strong cyclone centered over Chukchi Sea began breaking up ice in the BCE Region and affecting CAA (Canadian Archipelago) and the Central Arctic. In addition, most of the summer the Arctic Oscillation (AO) was in negative phase, meaning fewer clouds, more direct insolation and ice melting. More discussion of these two factors is at the end of this post.
The effects of this storm are seen in the rapid increase in water extent ( 482k km2 in one week) so that August 31 2015 had less ice than did 2014 at minimum September 19. Water extent continued to grow, and then stabilized once the storm abated and the AO went from negative to neutral. Now the ice is growing beyond the daily minimum.
Comparing MASIE and NOAA Ice Extents.
The table shows July 2015 was above 2014 but late August weather caused a drop in monthly averages. The August average shows ice extent dropped ~2.7M km2 from July, compared to a 2014 loss of ~2.0M. That difference persisted until the minimum was reached. NOAA typically reports a lower extent than MASIE, a difference that averaged ~300k km2. Then in one week MASIE dropped while NOAA plateaued, and until recently NOAA September extents were quite close to MASIE, some days showing a higher number.
With the September daily ice starting out lower than 2014 the monthly average will end up smaller. The September first 25 days average is shown, a figure that should rise and end the month over 4.6M km2. It is now evident the minimum has occurred, and the recovery is under way.
In any case, I am not alarmed over open water in the Arctic. Steadily increasing and above average September ice extents signify the coming of the next ice age, a genuine threat to human life and prosperity. Fortunately, that is not the indication this year.
Current and Recent Weather in the Arctic
In addition to the storm, the negative AO has been conducive to accelerating ice melting by increased insolation.
September 16 Arctic Oscillation Forecast from AER:
The AO, which has remained almost consistently in negative territory since late June, has resulted in near record low AO values for July and August. The AO is predicted to first trend positive through the weekend and pop into positive territory early next week. However by midweek the AO is predicted to return back into negative territory and remain negative through early October.
“The positive trend in the AO and the setting sun may have brought an early end to the Arctic sea ice melt season but not before sea ice extent achieved its fourth lowest value since observations began. It is likely that the extremely low AO values observed in July and August are reflective of atmospheric conditions (sunny and warm) that were conducive to rapid sea ice melt.”
The Alaska Dispatch News reported August 27 on the storm effects at Barrow, Alaska:
“The service has issued a coastal flood warning for Barrow until Friday morning, along with a high surf advisory for the western part of the North Slope and a gale warning for much of the Beaufort and Chukchi Seas. Seas up to 14 feet were forecast for Thursday in the Chukchi. . .Thursday’s high waves and flooding are products of a large storm that’s being felt as far as Southcentral Alaska, where high winds are forecast, Metzger said. “It’s a pretty big low-pressure system that’s over the Arctic Ocean,” he said. ”
This storm is reminiscent of the 2012 event that resulted in the lowest ice, greatest water extent this century. The high winds, waves and swells have several effects: Gales push ice floes, opening water between them and pushing them toward warmer waters; Ice pieces are churned and fractured increasing the melt rate; Wave action can flood ice packs or can cause compacting, further reducing extent.