The heat is already there. It's not so much that heat now present will melt the ice as much as it is, we are losing/have lost a heat sink that would capture summer insolation rather than the ice.
As Wayne posted elsewhere, such buoy data as we have suggests internal ice temperatures are very high - 10C or more higher than in the past. There is no buffer for the incoming melt season heat.
That's certainly symptomatic of bad things happening, but of itself I don't think the higher ice temp going in is a huge factor ; If I've got the numbers right, raising the temp of 1m3 of ice by 10 degrees requires ~19MJ, melting it takes ~ 302MJ on top of that.
What worries me is the prospect of the ice cover becoming so broken that when summer storms bring warm water from the outside, it will mix with the ice at the surface, rather than pass by underneath. That could make it all vanish overnight.
I'm not totally sure but I believe it should be double that, so more like 302 and 38. So melting of ice to water without a change of temperature (just the fusion energy or whatever it's called) requires the same energy as heating water by 80 deg
Hi Oren, I believe the specific energy of ice is a little less than half that of water (if the highschool chemistry page I found is to be believed) so 19 might be the correct number for ice.
That being said, if the ice overall is thinner and warmer by that much, it would mean that the melting season basically has about a 6% head start on previous years, because it needs about 6% less energy to get the same volume of ice to the melted state. If 6% more ice melted because of that, I'd say that's a fairly significant departure from normal.
Cheers,
Marcel
There is an important detail to take into account: the
rate of freezing, which in full Winter is roughly proportional to the difference of average temperature at the ice surface (-15 to -30 degC depending on location) and at the bottom (-2 degC). If this difference has been sustained in average say at 15 degC at a given location, instead of the normal 20 degC (see average temps for the Arctic 80+ even more extreme than this example), for
two months, it means a 25% less than normal growth rate during that time. I am neglecting snow cover insulation here, which is a lot to neglect, but even with snow cover, if temperature excess is sustained for months, freezing rate should be substantially reduced.
This is one manifestation of the heat excess that jdallen refers to. The heat absorbed to cool the ice is negligible compared to the heat being absorbed by bottom freezing, but, as said, that heat absorbed is proportional to the temperature diff bottom - top, and if this one is 10 degrees above average ...
Also, the reduced ice growth (6% ? for instance) means bottom melting would start sooner than normal.
So, I guess, sustained air temperatures above normal for months lead to reduced ice growth, which becomes more vulnerable in Summer.