Even though their ice is called 'eternal', many alpine glaciers' lives may come to an end within this century. For 150 years, most of them have been more or less constantly retreating, and since the eighties, their shrinkage has visibly increased.

The Furka Pass in central Switzerland has long been awaiting its visitors with a special attraction. Just below the highest point of the pass, tourists may enter an ice grotto dug into the Rhone glacier to discover glacier life from the inside. Each year however, the grotto's entry can be found a few metres further downhill. Long-term measurements reveal that from 1879 to 2010, the Rhone glacier has lost 1266 metres of its original length.

The Swiss Alps are often called 'Europe's water tower'. Nearly 60 billion cubic metres of water are stored in its glaciers. Matthias Huss, glaciologist and senior lecturer at the Department of Geosciences at the University of Fribourg explains that glaciers fulfil a balancing function: "They release water exactly when we need it, while storing it in periods when we need it less."

In other words, glaciers store water during the cold and wet winter months. From May to September, snow and ice melt on the glacier surface and provide the water that is dearly needed during the hot and dry season. That same mechanism also balances year-to-year variations: in colder, wetter years glaciers accumulate water that is released in relatively hot and dry summers like in 2003.

The threat posed to alpine glaciers' essential contribution has long been recognised. However, a new study presented by Matthias Huss in the scientific journal 'Water Resources Research' found that the proportion of glacier water running down major European streams is larger than previously assumed.

"I have compared water runoff data from glaciers with actual runoff at gauges along the entire length of four major streams originating in the Swiss Alps," explains the glaciologist. His study is based on measurements along the Rhine, Rhone, Po and Danube rivers.

The comparison allowed Huss to determine the relative share of glacier water running down those streams. "Consequently, I was able to quantify how much the runoff of those streams could decrease in case the glaciers' contributions are entirely lost," he says.

One of the streams observed by Huss is the Rhone. Originating in the Upper Valais in Switzerland, the river passes through the Rhone Valley and Lake Geneva to France, finally reaching the Mediterranean Sea at the Camargue Delta near Arles. The Rhone's length is 813 kilometres, its drainage basin measures about 100,000 square metres.

In August, snowmelt runoff from non-glacierized regions of the catchment is small, while bare ice melt is most important. According to Huss's calculations, the 100-year average glacier contribution to the Rhone accounted for 25 percent of the total runoff. In August 2003, the share deriving from glacier storage change rose to 40 percent; a proportion not to be ignored during that extremely hot and dry summer.

At Switzerland's Federal Office for the Environment (FOEN), researchers are well prepared to deal with the consequences of climate change for the Swiss water household. The FOEN recently started 'Project CCHydro'. The project name stands for climate change and hydrology in Switzerland. Based on current climate scenarios, the project aims to provide detailed forecasts on the hydrological cycle and runoffs in Switzerland for the coming decades.

Project director David Volken says that between 1996 and 2006, 0.9 billion cubic metres of water have melted from the glaciers yearly. He expects that until 2050, runoff from glaciers will increase, but then rapidly drop towards the end of the century.

"Because of the warming climate, snow melt will happen about a month earlier and rainfall will decrease 10 to 15 percent in summer," Volken adds. As a consequence, the rivers' runoff regime will change, he predicts. "There'll be more runoff in winter and less in summer. During hot summers, less water will be available in the future," the hydrologist warns.

Matthias Huss of the University of Fribourg also stresses that the current picture is deceptive. "Due to climate change, we currently get more water from the glaciers than normally, as they're melting. At first glance it looks like there's no problem," he says. But Huss warns that soon the picture will change and the remaining glaciers won't be able to provide enough water during the summer months.

Huss' glacier models are linked to specific climate scenarios. Diverging global warming estimates therefore affect prognoses regarding glacier shrinkage significantly.

The glaciologist admits that there are large uncertainties. "However," he says, "what's for sure is that glaciers will shrink massively. Even in an unlikely best-case climate scenario, glaciers will lose more than 70 percent of their size until the end of the century." And in the worst case? "There wouldn't be any glaciers any more at all."

Taking different glacier retreat scenarios into account, Huss estimates that currently glacierised basins might contribute 55 to 85 percent less water to stream flow runoff by the end of the 21st century. "Even if the climate could be stabilised at the current level," the glaciologist argues, "we'd witness drastic glacier retreat and their storage ability would either drop extremely or be lost totally."

As glacier shrinkage seems unstoppable, mankind will be forced to adapt to the new situation. Water shortages may occur more often and economic consequences may be harsh, the study warns. Especially the agricultural sector will face serious challenges, and communities may struggle to keep up drinking water supply.

The FOEN's Thomas Volken says that in the agricultural sector, water consumption efficiency has to be stepped up. He adds that adjustments in the cultivation of agricultural surface are inevitable, too.

As regards drinking water supply, Volken suggests its optimisation through regional integration and new strategies, such as linking drinking water networks to at least two independent resources. As additional measures, the hydrologist mentions the construction of additional dams in the mountains or systematic ground water accumulation.