The retreat of the glaciers in the Swiss Alps reached up to 150 metres, with an overall melting exceeding that observed in any year since measurements began in the 19th century, according to the Swiss Academy of Natural Sciences.
And the shrinkage of the mountain ice was not the direct result of record hot summer temperatures in Switzerland and Europe last year, it added.
"The overall view that emerges is of a clarity never seen before since annual measurements started in 1880. None of the glaciers progressed or were stationary," the academy in Bern said in a statement.
"These observations should not be associated directly with the extreme summer heat, the length of the glaciers reacts with a delay to the change in climate," it added.
One of the academy's scientists explained that the overall length of the glaciers reflected a warming of the climate over several years rather than immediate shifts in temperature.
More complex measurements of the thickness of the ice cover -- which is affected by short-term heat -- on three glaciers also showed melting last year exceeding the levels measured through the 1990s, said Andreas Bauder.
"The length change sums up all the climatic influences," he told AFP.
"The glacier measurements are one of the best ways of documenting climate change," Bauder added.
The academy also cautioned that the advance of some glaciers occasionally observed in recent years was caused by residues of old snow, and was not due to the freezing of new rainfall during cold weather.
Overall, glaciers in the heart of Europe's biggest mountain range stopped advancing about 50 years ago, Bauder pointed out.
The Swiss length measurements were based on regular data recorded on 96 Alpine glaciers.
Climate change has been blamed on global warming caused by the rise in air pollution from greenhouse gases such as carbon dioxide.
Bauder said scientists were not able to predict longer term trends for the ice floes but felt confident enough to forecast that the Swiss glaciers would again shrink in 2004.
"The glaciers will retreat, just on the signals we had in the last couple of years," he observed.