In the short term, the phenomenon may help increase the world's supplies of fresh water. But in the long run, the shrinking of the glaciers will mean a significant decline in fresh-water supplies from ice melt, leaving river levels entirely dependent on rainfall.
Reynald Delaloye is a research assistant at the Institute of Geography in Fribourg, Switzerland: "Except several exceptions, glaciers are withdrawing. This trend started approximately 150 years ago. But we observed in the past 15 to 20 years an acceleration of this withdrawal in many mountain ranges around the world."
In the Alps, the combination of warmer summers and drier winters, meaning less snow to feed the glaciers, is responsible for the glaciers disappearing.
"The Alpine glaciers in Switzerland have lost approximately 40 percent of their length [at their base] since 1850. During the same period their loss in volume are estimated at 50-60 percent. About 10-15 percent of the withdrawal has occurred in the past 15-20 years. For big glaciers, differences are often measured in kilometers," Delaloye says.
In the Alps, Delaloye notes, temperatures have risen by 1-1.5 degrees Celsius since 1850, and possibly two degrees in some regions.
There is little reason to be optimistic about the Alpine glaciers' future, as the emission of greenhouse gases by industrialized countries, which is held primarily responsible for the global warning phenomenon, is expected to grow further.
"If temperatures increase by another degree we may see a reduction of 20-25 percent of the glaciers' surface. If the warming reaches four or five degrees -- this is what is forecast for the coming century -- 80-90 percent of the glaciers' surface will disappear in the Alps," Delaloye says.
About 5,000 kilometers east of the Alps, a team of Kazakh, British, and German scientists have recently reported that climate change is responsible for the rapid melting and receding of the vast majority of glaciers in the Zailiiskiy Alatau range in southern Kazakhstan.
They have been working for the last five years in this part of the Tien Shan mountains (the "celestial" mountains), which stretch for more than 2,000 kilometers through Tajikistan, Kyrgyzstan, Kazakhstan, and neighboring China.
Stephan Harrison of the University of Oxford is leading the mission. He says that the 416 glaciers in the region have lost nearly two cubic kilometers of ice a year between 1955 and 2000 due to a small but pervasive rise in temperatures.
"There has been relatively small rise of about 0.5 degrees Celsius over the last 60 years or so in this part of Kazakhstan. But it's actually sufficient to melt the glaciers quite considerably. So between about 1955 and 2000 in the northern Tien Shan the glaciers have been reduced from something like 270 square kilometers in size to about just over 200 square kilometers in size. So that's quite a big reduction in surface area over the last 50 years. And that is caused by precipitation changes perhaps, but also by temperature rises," Harrison says.
Harrison says most glaciers in Kazakhstan -- like those in South America and Africa -- are expected to disappear completely over the next 20 years. Himalayan glaciers are also melting away at accelerated rates.
The shrinking and anticipated disappearance of many of the world's glaciers has potentially catastrophic consequences for communities that rely on ice melt for water for irrigation, drinking, and hydroelectric and nuclear power stations.
Harrison says many rivers in the upper ranges of the Tien Shan are glacier fed. The glaciers' disappearance, he says, will affect the livelihood of millions of people in Central Asia.
"The problem is that about 75 percent or so of the river run-off in the region, which is used for irrigation, comes from rivers which drain these glaciers. So in a sense the fact that these glaciers are receding very, very rapidly means that there are potentially very serious problems for irrigation schemes and water supply in the region," Harrison says.
A report from Salford University in Britain last year showed that the great rivers of Europe that are fed by glaciers in the Alps may run dry in summer seasons if the glaciers evaporate completely. Rivers fed from the Alps include the Rhine, the Rhone, the Po, and the Inn, which feeds the Danube.