The result of an international scientific paper, based on data and models from the Danish Meteorological Institute, is suggesting that an eventual meltdown of Greenland’s ice-cap is almost unavoidable. . . .Greenland has some interesting mechanisms of ice loss, some of which were unknown just a few years ago.
After 2040, on a time scale of 1,000 years ahead, it will not be possible for the giant Greenland ice-cap to be re-created and return to current levels.
“Over the next 30 years the amount of snowfall will not compensate for melting,” Hesselbjerg Christensen tells pol.dk adding: “Based on our model, I would almost say that the point of no return has already been passed. Our result shows in principle that permanent meltdown is unavoidable.”. . .
There is the obvious surface melting, which is how people would normally think of an ice sheet being lost: warm air, rain, etc. melts the ice from the surface.
The resulting melt water causes some other interesting effects. One is a lubricating effect. When melt water finds a crack in the ice, it wedges the ice open and can create a conduit that brings the water deep into the ice sheet, all the way to bedrock. This water both lubricates the flow of ice and warms the ice, softening it.
There has been some speculation that large masses of ice might get warmed and soften sufficiently that it won't be able to support its own weight. That would create episodes of "iceslides" if you will: sudden structural failure of city-sized areas thousands of feet thick. It would be quite something to see.
Another mechanism of ice loss from Greenland is warm ocean water melting glaciers at their outlets from below. Some glaciers in Greenland are grounded below sea level for quite a distance inland.
In the future it is expected that, as the height of the ice sheet is reduced by ice loss, the warmer air at lower altitudes will cause even faster melting. So, once the ice sheet loses a certain amount of altitude it will be impossible to stop further melting without significant cooling of the climate.
The complete loss of Greenland would raise sea level by an average of around 7 m. This process had been expected to take a thousand years or so, but the discovery of previously unknown mechanisms outlined above shortens the timeline significantly.
It is hard to say how fast this could go. Present warming is proceeding about 10x faster than at any time known from the geologic record. A couple of hundred years perhaps?
You would have to assume the loss of Greenland would be accompanied by the simultaneous loss of West Antarctica (~5 m worth of rise), which is even more unstable, as well as some unknown contribution from East Antarctica.
If you figure losing half of Greenland's ice mass in 200 years with an equal contribution from West Antarctica, that is 3.5 m (Greenland) plus 2.5 m (W. Antarctica) over 200 years or 3 m per century without even considering East Antarctica.
Previous deglaciations have produced sea level rises of 2.5 m per century and perhaps as much as 5 m per century, with a much slower warming.
Regardless, it is very difficult to see much more than about 1 m by mid-century.
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