Many of the world's mountain glaciers are melting at a faster rate than at any time in the past 150 years, according to the latest assessment by glaciologists.
Scientists believe that the Alps, in particular, are experiencing a rapid disappearance of glaciers formed during the last ice age more than 10,000 years ago.
The scale of the phenomenon is revealed in photographs of dozens of glaciers, taken several decades apart, which show how they have shrunk over the past century. Glaciers as far apart as Alaska and Austria, from Greenland in the north to the Andes in the south, are showing signs of an accelerating retreat that appears to be linked to climate change.
Michael Zemp and colleagues from the World Glacier Monitoring Service at the University of Zurich in Switzerland believe that warmer air temperatures in Europe in recent decades is behind the rapid loss of Alpine glaciers.
"Glaciers have been shrinking since 1850 but there has been a definite acceleration over the past two decades," Dr Zemp said.
The latest study shows that there has been a 50 per cent decrease in the area of the Alps covered by glaciers over the past 150 years. However, the rate of loss between the 1970s and 2000 was almost three times faster than the rate of loss seen between 1850 and 1970, Dr Zemp said.
In fact, the situation is even more dramatic because much of the loss between 1970 and 2000 occurred after 1985. And since 2000 there have been exceptionally warm years where glaciers have shrunk even faster than in previous years, Dr Zemp said.
"After the mid-1980s, glacial retreat in the European Alps really started to happen much more quickly than before. The summer of 2003 was particularly pronounced," he said.
From June to mid-August in 2003, a heatwave centred on France, Switzerland and northern Italy sent average temperatures soaring 3C above normal for these summer months.
Scientists estimated that the average glacier thickness of the Alps shrunk by about 3 metres during 2003, nearly twice the amount lost in the previous record year, 1998, and about five times more than the annual Alpine average. Alpine glaciers had already lost more than 25 per cent of their volume in the 25 years prior to 2003, and roughly two-thirds of their total volume since 1850. At this rate, about half of the total volume of Alpine glaciers would melt by 2025 and less than 10 per cent would still be ice by the end of the century.
Some glaciers, such as those in Norway, are expanding as a result of heavier snowfall linked with warmer air temperatures but most of the world glaciers appear to be in retreat, said Bruce Molnia of the US Geological Survey.
"There is no question that on a global basis we're seeing a warming that goes back several centuries. There are 2,000 glaciers that descend to below 1,500 metres in Alaska and about 99 per cent of them are retreating," Dr Molnia said.
The loss of glaciers is probably part of a natural process that began with the ending of the last ice, but man-made climate change could also be playing a role.
"Global warming is one factor, but if humans went extinct, glaciers would still be in retreat," Dr Molnia said. "Should we be worried? If glaciers are the source of your drinking water or if you live in an area that is vulnerable to sea-level rise, then yes, you should be worried. But in the longer term, the advance and retreat of glaciers is part of a natural cycle."Reuse content