You may have seen images like this before, demonstrating the progressive summer melting of the Greenland ice sheet:
Then in July 2012 this happened:
Yes, it was unusual, but not unprecedented. Ice cores show that this happens every 150 years or so, and it last happened in 1889. That said, weather patterns have been unusual at high latitudes in the northern hemisphere, and these changes have been linked with climate change. In this case it was a combination of warmer weather and cloud cover that did the trick.
In terms of ice mass loss, a few days is not going to make much difference. The ice sheet is up to three kilometres thick and at high altitude the water will refreeze. Near the edges the water may end up in the ocean. This can happen through moulins, where the water falls down into the ice sheet via a crevasse, typically to the base of the sheet, which can lubricate the gradual movement of the ice. This is a classic photo of a moulin:
Not sure I’d stand where those blokes are standing! This diagram shows how it works:
The underlying topography of Greenland is not conducive to losing the whole ice sheet. In the centre it’s below sea level and has jagged mountains around the edges, a bit like a saucer. This NSIDC image gives the basic idea.
Of course the ‘mountains’ are vastly smaller than that in true scale.
Graphs like this one from Hansen can get us excited:
Certainly the mass loss is worrying. In terms of the next century, however, it is too early to tell how fast the rate of loss will increase. James Hansen shows the effect that a 10-year exponential doubling of ice sheet melting can have late in this century:
The shape of what’s to come is likely to be somewhere between the two, but less than either.
The IPCC report of 2007 showed the relative contribution of the four main sources of sea level rises – thermal expansion, glaciers and ice-caps, Greenland, and Antarctica. So far the ice sheets are playing a minor role. This is certain to change, but gradually. Here is the table from the IPCC report:
In 1993-2003 Greenland accounted for only 0.21mm in annual sea level rise of 3.1mm.
It is likely, though, that we are getting into the zone where the Greenland ice sheet will be seriously compromised as we move above CO2 concentrations of 400 ppm.
Just in, the north pole is now making a beeline towards Greenland, courtesy of melting and ice loss. That’s impressive even though it’s only moving a couple of centimetres per year!
New Scientist has an article (paywalled) telling us that sea level changes will be quite uneven around the world. If all the ice on Greenland melts, for example, sea level will actually fall in that area! Two reasons are given. First, the lifting the weight of the ice will see the land surface rise. Secondly, there is a gravitational pull between an ice mass and the surrounding water in the ocean which pulls the water towards the ice!
The way things are expected to work, Europe will benefit, but the east coast of the US will be unlucky with sea level rises up top 25% higher than expected. The water from melted ice has to go somewhere. South America will be adversely affected.
There is a copy of the text of the article here without the pictures.