The current contribution to sea level rise is mostly from thermal expansion of the oceans and the melting of glaciers and small ice caps. Two of the largest contributors to this rise in sea level are the melting glaciers in Greenland and Antarctica, for they make up 99% of the glacier ice on earth. In both regions, glaciers are melting at an alarming rate.
Ice in the arctic sea is also melting at an alarming rate. But, because most of this ice is already part of the sea, it does not make a large contribution to sea level rise . . . even though it does contribute to climate change in other ways. As Arctic sea ice melts, there is a loss of reflectivity (albedo) of the sun’s rays. And, because water is much darker than ice, more sunlight penetrates into the water, thus raising its temperature. This, in turn, contributes to the release of methane gas that has been stored in the sea for eons.
Greenland has shown a rapid response to warming. It’s glaciers are showing an increase in flow speed, frontal retreat, and thinning of the ice. About half of the loss is due to melting, while the remainder is due to blocks of ice breaking off into the sea, in a process known as calving.
Though, on average, about half of the surface of Greenland’s ice sheet naturally melts each summer, most of that melt water quickly re-freezes in place. But if the annual average temperature on Greenland increases by about three degrees Celsius, then the ice sheet might melt at a rate which will tip it into a new, smaller inland form.
Though there is much uncertainty about this, Greenland may be at such a tipping point right now. The two videos below give a good introduction to this issue. The first one is an 11 min. CNN report that includes some very spectacular photography. The second one is a 6 min. PBS Nova presentation. Both are well-worth the time.