With the rise in the global mean temperature, some glaciers are retreating. It is predicted by the Intergovernmental Panel on Climate Change that worldwide, mountain glaciers will undergo a striking retreat, with most glacial-fed rivers and streams experiencing significantly diminished summer flows. As the glaciers retreat, a crucial source of fresh water in many tropical countries disappears. These areas are already water-stressed.
The alpine ice masses have been reduced by about 50% since 1850. More recently, map makers cannot keep up with the expansion in size of glacial lakes consequent on the melting of glaciers. Massive recession of glaciers has happened in the Himalayas, the Alps, Africa (Kilimanjaro and Mount Kenya) and the South American Andes. The climbing and skiing resort of Chamonix is under threat in the long-term, as the peaks around Mont Blanc begin to lose their ice. The north face of the Eiger used to have three massive ice fields, reduced to one dwindling remnant. There is also concern that swelling glacial lakes in the Himalayas could burst their banks and obliterate whole villages.
It was reported in 2002 that Alaska's glaciers are melting more quickly than previously believed. Despite their relatively small land mass – about 13 percent of the world's total mountain glacier area – Alaska's glaciers contribute about half of all sea rise caused by glacial melt and about twice as much as the amount of water lost from the entire Greenland Ice Sheet. The rate of thinning has doubled in the past five years, compared to the 40 years before. As a result, the Alaskan contribution to sea-level rise has doubled, to about 0.27 mms a year during the past decade, or about twice the amount assumed by an international panel of scientists in 2001 that predicted sea level would rise up to 11 centimetres (about four inches) by the end of this century due to global warming.
Glaciers are the water towers of the world – vital for storage. If they are melting fast this has grave implications for the people who live locally but is also a sign of global warming.
There is some indication that glaciers in wet maritime environments have tended to increase in mass in recent decades whereas some glaciers in dry, continental climatic areas have shown a tendency to lose mass.