By Jonathan Amos
Science reporter, BBC News, San Francisco
Swiss glaciers are melting away at an accelerating rate and many will vanish this century if climate projections are correct, two new studies suggest.
One assessment found that some 10 cubic km of ice have been lost from 1,500 glaciers over the past nine years.
The other study, based on a sample of 30 representative glaciers, indicates the group's members are now losing a metre of thickness every year.
Both pieces of work come out of the Swiss Federal Institute of Technology.
"The trend is negative, but what we see is that the trend is also steepening," said Matthias Huss from the Zurich university's Laboratory of Hydraulics, Hydrology and Glaciology.
What really matters is how much ice we have in the big glaciers, because the small ones will disappear; that seems clear
Daniel Farinotti, Swiss Federal Institute of Technology
"Glaciers are starting to lose mass increasingly fast," he told BBC News.
The retreat is being driven largely by longer melting seasons. The other key factor in glacier health - the amount of winter snowfall to replace ice melt - shows no long-term changes.
The two studies are being presented here at the American Geophysical Union's Fall Meeting, the world's largest annual gathering of Earth scientists.
They are not the first to assess the status of Swiss glaciers but few others can match their scope.
In one, Daniel Farinotti and his team tried to assess the total volume of ice in Swiss glaciers - 1,500 of them, from the mighty Aletschgletscher (the largest glacier in the Alps) to small ice fields that cover less than three square km.
The research used direct measurements where available, and combined this with modelling to estimate ice volumes for areas that are data-deficient.
The assessment found a total ice volume present in the Swiss Alps of about 74 cubic km by the year 1999 (a baseline for the purpose of the study). It is a bigger figure than previously thought.
"However, 1999 is quite some time ago now, so what we did was try to calculate the volume lost since this baseline; and we estimate a figure of 13% - from 1999 to today," explained Mr Farinotti.
For 2003, remembered for its strong heatwave across Europe, the team estimates that 3-4% of the volume in Switzerland at that time was lost in that one year alone.
Mr Farinotti said his study highlighted the importance of the largest glaciers as ice reservoirs: more than 80% of the total ice volume is stored in the 50 largest glaciers.
"Aletschgletscher, for example, has about 12% of the area of Swiss glaciers but it contains about a quarter of all ice that is present in Switzerland," he told BBC News.
"What really matters is how much ice we have in the big glaciers, because the small ones will disappear; that seems clear. For them, it's just a matter of years. But in glaciers like Aletsch that have a lot of ice, they will be around for decades."
THE DECLINE OF FOUR SWISS GLACIERS SINCE 1860
The four glaciers here represent a range of types, sizes, locations, and climatic zones. The assessment has now been extended to 30 glaciers
Area covered by the glaciers - Aletsch: 83.01sq km; Rhone: 16.45sq km; Gries: 5.26sq km; Silvretta: 2.89sq km
Distinct phases of growth (I & III) and strong ice loss (II & IV) are seen within an overall trend for the period which is negative
The cumulative mass balance is given in "metres of water equivalent". Essentially, it records the net thickness change of the glaciers
Thickness change over the entire period - Aletsch: -65m; Rhone: -43m; Gries: -97m; Silvretta: -35m
The study by Mr Huss and his team takes a slightly different approach. It considers just a key group of 30 glaciers, representing all sizes, types, and locations.
Again, using a mixture of direct data and modelling, the scientists analysed the mass trends from 1900 to 2007.
Over this period, there is a significant negative trend. It is not linear, however. There are two distinct phases when glaciers gained mass, and even a phase in the 1940s when the glaciers lost mass faster than they do now.
But in general, over the period, there is a retreat; and in the last 30-50 years, the shrinkage has accelerated.
Mr Huss has applied future climate projections to the 10km-long Rhone Glacier, which in Swiss terms is mid-sized.
"Rhone Glacier will have almost gone in 100 years," said Mr Huss.
"It first retreats not very fast, until about 2050. Then, it retreats really quite fast. It means that most glaciers, the smaller ones, will have disappeared by the end of this century."
Switzerland's glaciers are iconic but their shrinkage is more than just an issue for the tourists with their cameras; their loss would have profound ecosystem and economic consequences.
"Glaciers store the water in winter and release it in the summer when it is dry and warm when there is more need for water," added Mr Huss.
"And they can also store it in the wet and cold years and release it in the hot and warm years. That's an important reservoir.
"In the south-western part of Switzerland, almost all run-off water from glaciers is temporarily stored and used for electricity production. More than half the electricity consumed in Switzerland is produced from hydropower."
The Huss-led research builds on work published in the Journal of Geophysical Research this year. The Farinotti-led research has been submitted to the Journals of Glaciology, and the Journal of Global and Planetary Change.
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