Now, though, a further threat is starting to emerge: tsunamis.

The idea may sound bizarre. After all, killer waves are perceived as a threat to coastal communities, vulnerable to walls of water unleashed by giant earthquakes.

That was the case in the December 26 tsunami that scoured shorelines around the Indian Ocean, killing 284,000 people.

But European specialists say there is also a risk in the mountains, from huge lakes of meltwater that build up behind glaciers. If the icy barrier is breached, communities downhill are at risk of being swept away.

"In the Himalayas, some glaciers are up to 70 kilometers (43 miles) long," said Martin Beniston, a climate scientist at Freiburg University in Switzerland.

"In Bhutan alone, there are at least 50 lakes in this category, and a similar number in Nepal as well. Towns and villages in their path could be hit by a torrent of water like a Tsunami," he told AFP.

The unusual phenomenon came to light last October in France's Savoie region, says Christian Vincent, a research engineer at the Glaciology Laboratory in Grenoble.

A huge lake, five hectares (12 acres) across and 25 metres (81 feet) deep, formed at the back of the Rochemelon glacier at an altitude of 3,218 metres (10,450 feet), due to summer heat that had melted part of the glacier.

The discovery prompted the intervention of engineers, who decided to drain the lake to avoid the risk that the glacier wall could erode and then crack open.

A series of studies over the past five years has accumulated evidence that glaciers are in retreat in the Andes, the Alps in western Europe and the Himalayas, thanks not only to warmer temperatures but also shorter or less prolific seasons for snowfall.

The global benchmark is Austria's Pasterze glacier, whose length and volume are measured by a NASA satellite.

A computer model of the Pasterze, devised by the University of Utrecht in the Netherlands on the basis of data sent back by the satellite, suggests that all of the glaciers in the Alps may disappear by 2080, according to Austrian specialist Heinz Slupetzky.

Chinese glacier expert Yao Tandong, director of the Institute of Tibetan Plateau Research at the Chinese Academy of Sciences, last year said as much as 64 percent of China's high-altitude glaciers may vanish by 2050 if current warming trends continue.

Each year, its Himalayan glaciers shrink by an amount equivalent to all the water in the Yellow River, he said.

Glacier loss not only has an impact on tourist businesses that need a picture-postcard image for visitors.

Twenty-three percent of China's 1.3 billion people live in oases in the arid west of the country that ultimately depend on glacier runoff for their water.

Glaciers "are a capital in freshwater which is rapidly being exhausted," says Italian climatologist Luca Mercalli, president of the Italian Meteorological Society.

Global warming is the term for rising temperatures on the Earth's surface, caused by "greenhouse" gases emitted by burning fossil fuels.

This pollution lingers in the atmosphere, trapping solar heat instead of letting it radiate back into space.

Since 1900, Earth's surface temperature has warmed by 0.7-0.8 C, and a rise of another 5 C (9 F) may occur by the end of the century if emissions are not braked.

The first treaty aimed at curbing greenhouse gases, the UN's Kyoto Protocol, enters force on Wednesday, but scientists say it falls way short of what is needed to tackle the problem.

All rights reserved. � 2004 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.

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