We lost 60% of the ice thickness and by extension 60% of the total ice M between 1957 and 2000. If we conservatively assume that the loss rate was the same throughout this period, the annual loss rate R can be discovered by the simple equation:
C = M - 43R expressed as percentages and C been the current percentage of the original M(1957).
Therefore R = (M-C)/43 or: R = (100 - 60) /43 or: R = approx. 1% of M
The apparrent current loss rate can be calculated by dividing 1% by 40% remaining to give us 2.5%.
Except that it is obviously faster than this. If we project that the prinicipal warming only seriously started in the early eighties, we have instead R = 2% and a current effective loss rate of 5% which actually appears to match current experience. This also means that in the last seven years we have lost an additional 14% of the original M leaving a current C of 26% or only 13 more years,instead of the more sedate forty years.
On top of all that the clearing of the majority of the Arctic ocean is allowing a greater heat absorption than usual and a thinner winter icesheet this winter.
I think that we actually have as little as ten years of summer sea ice cover left and that further warming will eventually expand the clear season to early August.
As stated earlier, the only thing that is going to halt this runaway is a major cold snap, perhaps caused by an injection of SouthPolar water into the South Atlantic. A late summer cruise along the northern coast of Ellesmere Island with a short hop to the North Pole in 2016 is very appropriate and on my to do list.