By Alex Kirby BBC News Online environment correspondent in Bishkek, Kyrgyzstan

The water level in a remote central Asian lake has risen markedly since 1998, suggesting that global warming is now a reality.

Scientists here say they believe the rise is linked to climatic changes.

We should expect large increases in temperature and rainfall in this part of central Asia

Dr Mark Collins, Unep

They think the rise could affect the strategic balance of resources in the region.

What is happening appears to bear out climatologists' predictions of changes in central Asia.

The disclosure of what is happening comes on the eve of the opening of the Global Mountain Summit here, organised by the Government of Kyrgyzstan with the support of the United Nations Environment Programme (Unep).

Delegates from more than 60 countries are expected to attend, to discuss how to counter threats to the world's mountainous regions ranging from farming and development to natural hazards, human conflict and global warming.

Warmer, wetter

The lake at the centre of concern is Issyk-Kul, a huge expanse of water in the north-east of Kyrgyzstan, near the Chinese frontier.

Since measurements began in 1927, there has been a definite trend towards shrinkage, with the water level dropping steadily.

There have been occasional short episodes when it has risen. But since 1998, the level has risen by 26 centimetres, a remarkable amount given the lake's surface area of more than 6,000 sq km.

One person in two depends on mountain water (Image: T Natiano)

Dr Radzimir Romanovskiy is head of laboratory services at the Institute of Water Resources and Hydroenergy in Bishkek. He told BBC News Online: "We think the climate has been changing here over the last 30 years, becoming warmer and wetter.

"We're getting more rain and snow here now, and that's showing up in the lake. It does seem to be linked to climate, though the reason why the water level is rising is because of more rain falling and feeding the rivers that flow into Issyk-Kul.

"Melting glacier water is playing only a small part in all this. Of course, with predictions that the climate here will become warmer and wetter, you might expect increased evaporation to lower the lake's level.

"But I think the higher rainfall will be the more important factor. We've also found temperature changes deep in the lake. It's risen from 3.7 C to 4.2 C in parts."

Drying deserts

Dr Mark Collins, director of Unep's World Conservation Monitoring Centre (Unep-WCMC), told BBC News Online: "The lake level rise the Institute is reporting is significant, and so is the rise in core temperatures in the lake.

"The findings bear out the climate models which suggest we should expect large increases in temperature and rainfall in this part of central Asia.

"But what the changes may mean in environmental and economic terms is much harder to assess. Perhaps the high-level ecosystems here are not suffering as they are in Africa.

"Perhaps Issyk-Kul may become an ever-more important regional resource in central Asia, where the deserts are drying out. And of course the lake level rise could be a warning of a flood risk downstream."

Kyrgyzstan has another reason for concern about what happens in the world's mountains. Although it has no nuclear power of its own, it harbours 25 known dumps of nuclear material left behind by the old Soviet Union.

The country is an earthquake zone, and there is anxiety here about what could happen to the dumps if there were a large seismic shock in Kyrgyzsrtan. The conference is due to end on 1 November.