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Once the ice is fully surrounded by ocean, it will disappear very rapidly. Within the Arctic Ocean proper (i.e. the area currently covered by ice), the more open water, the faster the melt.
The ASI maximum Extent in the Arctic Ocean basin is constrained by land. Thus in the colder years of the 1970s and 1980s there was a cap on how much Extent the high Arctic seas could contribute. The recent increase of open water around the periphery of the Arctic Ocean that is able to absorb solar radiation early in the melting season could be an accelerating factor as Binnto notes. And previous reductions in ASI did not show up in the annual maximum Extent values because there was still enough Extent at the winter max to reach the land boundary edges. But as ASI reductions progress, the maximum Extent fails to reach the land boundary at an increasing number of locations. Once that begins to happen regularly, any further reductions do appear as a smaller contribution to the total Extent at maximum.
The increase in fall and early winter cooling from more open water going into the winter refreeze season is a negative feedback that has almost kept pace with increasing summer melt. There was a great paper posted by Gero on that topic: see
https://forum.arctic-sea-ice.net/index.php/topic,2348.msg354450.html#msg354450. If you read only one ASI journal article this year, that is the one to read IMHO. It deposes the "Slow Transition" theory. It showed that as summer melt has increased over recent decades, winter refreeze has increased almost as much, thus compensating for the increasing summer melt, thus the "Slow Transition". That is, until now.
The study found that going forward, melt season losses will continue to increase AND winter refreeze has passed its peak and is also declining. Thus winter refreeze ceases to be a negative feedback and begins to become an additional source of year-to-year decline. The winter refreeze decline slope is almost level for the next few years, but as we get farther past the crest of the hill, the negative slope increases. This all means (to me at least) that the relative stasis in annual minimum Ext/Area/Vol that we have seen for the past 10 years is going to end soon. And that the year-to-year annual decline in annual minimum values will progressively increase.
I do not know if the projections for the continuation of the trend for increased melt season losses and a change of direction from winter refreeze increases to a negative trend account for qualitative functional changes that could accelerate negative trends for both (i.e. more wind fetch and wave action, thinner/younger/more saline ice, less mechanical resistance to pack shattering, halocline thinning, more warm air or cyclone incursions, and the rest of ASI doomer catechism). If not fully accounted for in those projections, one of more of these other factors could add gasoline to the fire as a systematic change in Arctic behavior that would result in a major increase in losses.
The fact that nobody saw 2007 or 2012 coming beforehand, and that science can barely explain those years even with the benefit of hindsight indicates that we underappreciate the dynamism of ASI. That applies to either direction, up or down. But these days everything about ASI seems to be mostly down.
The geographic argument is pertinent, i.e. that ice at 90 north stays colder and is less likely to get warm enough to melt than the ice at lower latitudes that began melting out in the 1990s, 2000s, 2010s). But down here at midlatitude, the average temperature bands have moved northward at about 4km per year in recent decades (and that rate is probably increasing). It does not sound like much that becomes 40+km per decade. So even though the north pole hasn't moved, the warm air is moving north to gradually erode some of that geographic protection. (No change in the geographic distribution of solar radiation AFAIK).
There may be other negative feedbacks not accounted for in this view. My bias towards positive feedbacks may interfere with noticing negative feedbacks that may also increase with further ASI declines. But the "more open water in fall = more ocean heat loss" and the "ice at the highest latitudes stays colder" are the only ones I know of, and those two do not seem likely to hold out much longer.
I have to think that the models that show a slower rate of decline over the next 30 years, and no accelerating blowouts, account for everything listed here. So my "knows just enough to be dramatically wrong" analysis may be overly simplistic and overblown. But it is also true that the expert models for ASI have consistently underestimated the rate of decline, did not predict the qualitative system change of the huge losses in MYI in the early 2000s, and did not expect that a year like 2012 was at all likely (though even 2012 may have been within the 99% confidence interval for the result distribution of various models).
