Over the last two decades the loss of ice from the Greenland ice sheet has increased fourfold and has contributed to the global rise in sea level. Nevertheless, the chain of events and physical processes that contributed to this has still not been established. One probable trigger for the acceleration and retreat of the glaciers that contributed to the loss of ice is the warming of the ocean.
The Greenland ice sheet has an area of 1.7 million square kilometres, a layer of ice 2 miles thick that covers Greenland. At its edge the glacier is thinned. Coastal fjords cut more than 600 metres deep – thereby exposing the edges of the ice sheet to contact with the ocean. The waters of the northern Atlantic Ocean that surround southern Greenland are at present the warmest of the last 100 years. The warming is due to natural climate variability and anthropogenic climate change. It is therefore important to understand whether the present warming of the ocean has contributed to the loss of ice from the Greenland ice sheet, and how future warming may lead to even greater loss of ice.
Studies of Greenland and the fjords have shown that when the northern Atlantic Ocean heats up, the warm waters quickly reach the fjords and, as a consequence, penetrate the channels of the Greenland glaciers.
Warming of the atmosphere leads to an increase in surface melting above the ice cover, and the runoff increases melting below the surface. Surface meltwater falls through cracks in the glacier, creating a freshwater river that falls into the ocean at the base of the glacier, sometimes from a height of up to 600 metres. The river quickly mixes with the salty sea water, which promotes the transfer of heat from the ocean to the ice, with the result that still more ice melts below the surface of the sea.
This process can be described as follows: "If you put an ice cube in a glass of water and do not touch it, it will take several minutes to melt. But if you stir the water in the glass, you make the ice more accessible to the warm water, and it will begin to melt faster".
Oceanographers are also concerned that this increase in fresh water at the surface of the northern Atlantic Ocean may act as a "lid", preventing the transfer of heat from the ocean to the atmosphere in the circulation system.