The third and last Sea Ice Outlook of this year has been published. The SIO is organized by the Sea Ice Prediction Network (as part of the Arctic research program 'Study of Environmental Arctic Change', or SEARCH), and is a compilation of projections for the September 2016 Arctic sea ice extent, based on NSIDC monthly extent values. These projections are submitted by professionals as well as amateurs (public outlooks).
Here's the summary for the August report:
This month the median pan-Arctic extent Outlook for September 2016 sea ice extent is 4.4 million square kilometers (km2) with quartiles of 4.2 and 4.7 million km2, which is slightly higher than July's value (4.3 million km2) (See Figure 1 in the full report, below). If the median Outlook should agree with the observed estimate come September, this year would be the third lowest September in the satellite record. The spread in the Outlook contributions narrowed slightly from July to August, with an overall range this month of 3.7 to 5.2 million km2.
The full range of Outlooks submitted this month lies within the range of the ten lowest years of sea ice extent in the observational record. As in July, no Outlook is predicting a new record this year, despite the warm winter, record low extents for every month in 2016 except March and July, and evidence of thin ice in spring. Current sea ice extent and meteorological conditions suggest a record low is unlikely, as surface temperature over the central Arctic has been near normal in the last two months and forecasts of atmospheric temperatures for the next few weeks indicate average surface temperatures. However, a major storm in the central Arctic during mid- to late August will support continued breakup of the central ice pack. The higher end of the predictions is also unlikely given that the current extent as of 16 August is 5.3 million km2.
And here's the figure showing all the projections (click for a larger version):
The September minimums for the last 11 years (in million km2, found here):
The results from the poll on the Arctic Sea Ice Forum show that median and average went up some more, as did the bin that received the most votes. Maybe the results would've been somewhat lower given the spectacular storm that currently rages up North, but as it stands the ASIF poll still has 2016 ending up second, whereas the SIPN SIO has it coming in third.
Looking at individual entries for the SIPN SIO, it seems that both the PIOMAS and CPOM predictions will probably end up too high. Both are based on models that revolve around two very important components: ice thickness and melt pond fraction. As useful as the model results are, by themselves they are not always enough to predict the final outcome of a melting season. Other components play an equally important role, like total Northern Hemisphere heat absorption that citizen scientist and ASIB regular Rob Dekker calculates using three variables: land snow cover, ice concentration, ice area.
As I wrote back in May, all three variables have been exceptionally low during the early stages of the melting season, and are making themselves felt in this final phase, spurred on by yet another cyclone, which may prove to be even more powerful than the Great Arctic Cyclone of 2012.
And then there's the wild card that no one really has a handle on: Ocean heat flux. As Ron Kwok and the late Norbert Untersteiner wrote in this 2011 article: "The surplus heat needed to explain the loss of Arctic sea ice during the past few decades is on the order of 1 W/m2. Observing, attributing, and predicting such a small amount of energy remain daunting problems." The ocean contains a lot more energy than 1 W/m2, but how much of this energy reaches the Arctic and its sea ice, is very difficult to measure. And because it's difficult to measure, it's also difficult to model.
One can only imagine what would have happened if the melt pond fraction had been higher, or overall thickness lower. I think the record would have been broken easily. This year will teach us a lot about how the first ice-free year might look. I always thought it would take a year like 2007, involving lots of open skies and compaction, but if the ocean is providing enough heat (either directly or via Ekman pumping), stormy weather will actually work better.
But let's see how things play out exactly before drawing conclusions. In 5-6 weeks we'll know which predictions were closest to the minimum.