"In the last 140 years it has moved back three kilometres (two miles)," Laudo Albrecht, a Swiss nature conservation expert said, standing on a ridge above the sweating glacier.

He was clutching a graph which also shows that the ice flow has melted faster in the past decade or two, and this summer's heatwave is likely to deepen the trend.

The Aletsch and the immediate area were designated a World Heritage site in December 2001, not only because of the spectacular nature of the landscape of rocky peaks, wooded slopes, meadows and glaciers, according to UNESCO.

The UN's Educational, Scientific and Cultural Organisation also explained that "the global phenomenon of climatic change is particularly well illustrated in the region".

Albrecht pointed across the valley to a contrasting band of colour along the opposite slope, like a trace of grime on an emptied bath. It shows that the Aletsch has lost about 200 metres (660 feet) in depth along most of its length since the 1860s.

The layer of ice is now 100 to 150 metres thick near the foot of the glacier, below the southern Swiss mountain village of Riederalp.

"This summer fits the developments of the past decade, that's what worries me. Not that this summer is so hot or dry, but because it fits this trend," Albrecht, who has been observing the glacier for 20 years, said.

Switzerland has been ailing under record high temperatures for more than two months, with a peak over 41 degrees Celsius (106 Fahrenheit).

Despite the cool wind generated by the huge mass of the glacier, the temperature at an altitude of 2,000 metres (6,600 feet) hovered around 25 degrees Celsius (77 Fahrenheit) in the shade.

Albrecht set foot on the Aletsch for the first time this year on June 10. He returned a month later and found that the end of the ice flow had retreated five metres (16 feet) further up the valley.

On the steep slopes around Riederalp, farmers are struggling to comfort their cows. Sprinklers create patches of green among the parched Alpine meadows.

The herds amble along mountain tracks, sending clouds of dust billowing in the air, and gather around water holes.

Albrecht, who was born and raised in this hardy, mountainous region, heads an information centre set up by the Swiss nature conservancy foundation, Pro Natura, in Riederalp.

He is the first to point out that exceptional weather has happened before, and insists that he always highlights the wonders of nature before he mentions the stresses and strains to visitors.

Yet, he now firmly believes that climate change is not simply a natural phenomenon, but that a human hand -- pollution -- is helping it along.

"If you want to change people's behaviour, you need time. The question I now ask myself is, do we have enough time?" Albrecht commented.

"We've had extremes like this before, to some degree it's a normal part of nature. But what disturbs me is that we have extremes frequently now, in some years storms, or other years without rain."

Swiss authorities have warned that the hot, dry conditions have triggered landslides and rockfalls, and made conditions for mountaineers even more precarious.

Albrecht sees another danger. When thunderstorms return and rain starts to fall again on the hardened ground, torrents will sweep loose material down into the inhabitated valleys below.

In 1993, the nearby town of Brig was hit by a torrent of mud and rock carried by a river, cloaking the streets in a deep layer of hardened mud and killing two people.

"It's profoundly disturbing, our living environment is being changed. Nature can live with that, but the question is, can we?" Albrecht observed.

This summer, the increased flow of water from the melting ice is exceeding the needs of hydroelectric power plants. A dam below the Aletsch is opened occasionally to stop it overflowing, according to Albrecht.

That can bring dangers: two tourists were killed recently on a nearby river bed after water was released upstream.

It can also bring short-term benefits: local Swiss power companies are exporting electricity to Italy, less than 20 kilometres (12 miles) away, where record low water levels in rivers caused by the heatwave have prompted power cuts.

Yet even those who have the most to gain from the power trade do not think it is worth it.

"With the glaciers, our future capital is melting," an executive for the power firm EOS told the Swiss newspaper Le Temps.

TERRA.WIRE