The political stability of a key central Asian state could be imperilled by climate change, researchers say.
By Alex Kirby
BBC News Online environment correspondent
They say glaciers are melting so fast in parts of Kazakhstan that the livelihoods of millions of people will be affected.
They found the area's glaciers were losing almost two cubic kilometres of ice annually during the later 20th Century.
With regional temperatures rising, they believe climate change is responsible.
The scientists, led by Dr Stephan Harrison of the University of Oxford, reported their findings at the annual conference in London of the UK's Royal Geographical Society and Institute of British Geographers.
They concentrated on the Zailiiskiy Alatau range of the northern Tien Shan mountains, which stretch through Kazakhstan and its neighbour Kyrgyzstan, and into China (the name means "the celestial mountains").
The mountains, which run for 2,000 km (1,250 miles) along the north-west edge of the Tibetan plateau, form an important climatic barrier between the Siberian and central Asian air masses.
Long observation period
There are 416 glaciers in the region, covering 510 square km (197 square miles).
Dr Harrison and his colleagues, from the University of Newcastle, UK, von Humboldt University, Germany, and the Kazakh Academy of Sciences, say they have been losing nearly two cubic km of ice a year between 1955 and 2000.
TIEN SHAN RANGE
The Tien Shan range runs across China, Kazakhstan and Kyrgyzstan
Between 1974 and 1990, the glaciers lost 1.28% of their volume each year.
The Tuyuksu glacier, 30 km (18 miles) south of Kazakhstan's largest city, Almaty, has been monitored by the country's scientists since 1902, with less detailed observations dating back to the 1870s.
Since 1923 it has receded by nearly a kilometre, losing about 51 million cubic metres of ice.
The team says these changes have serious implications for river runoff, and therefore for Almaty's water supply.
Many of the rivers which supply the irrigation schemes essential to agriculture are fed by glaciers and permafrost in the upper ranges of the Tien Shan, so the livelihoods of millions of people will be affected.
The glaciers keep the plains alive
The authors say not only Kazakh agriculture and development will be jeopardised but the political stability of a swathe of central Asia, as many of the rivers and glaciers cross state frontiers.
Kazakhstan uses about 90% of its water for irrigation, with an efficiency of only 40-60%, and it is adding 9,000 hectares (22,000 acres) to the irrigated area every year.
The scientists say the glaciers' "consistent pattern of retreat over the latter part of the 20th Century... is associated with a small but pervasive rise in mean annual temperatures".
Many Kazakhs face a drier future
Dr Harrison said: "The effects of global warming on glaciers are not just of interest to scientists, as glacial retreat has profound political, economic and social repercussions."
He told BBC News Online: "I think we can be certain the reason why the Tien Shan glaciers are melting is climate change.
"We have the climate records themselves, which go back to early last century. Sceptics often argue that records of this sort are contaminated by the proximity of urban centres.
"But these records are from glaciers 3,000 m (9,800 feet) up, nowhere near any towns or cities.
"They're confirmed by the evidence from tree rings, which preserve a record of climate conditions as they grow, and by the meteorological records.
"Taking all three together, I think we have to say that climate is affecting the glaciers."