Global warming is melting snow and ice on the world's highest mountain at an accelerating rate, researchers have claimed.

A study by a team led by a Nepali scientist at the University of Milan has found that glaciers on or around Mount Everest have shrunk by 13% in the last 50 years with the snow line 180 metres higher than it was 50 years ago. The glaciers are disappearing faster every year, it says.

The 60th anniversary of the first ascent of the 8,848 metre (29,028ft) peak by Sir Edmund Hillary and Sherpa Tenzing Norgay will be celebrated next week.

The researchers say they suspect that the decline of snow and ice in the Everest region is a result of changes in global climate caused by human-generated greenhouse gases. However, they have not yet established a firm connection, Sudeep Thakuri, who led the team, said.

The landscape around Mount Everest has changed dramatically since the world's highest mountain was first climbed. Mountaineers now report more rock and less snow and ice on well known routes. The ends of glaciers around the peak have also retreated by an average of 400 meters since 1962, the new research found, and some smaller glaciers were now nearly half the size they were in the 1960s.

The researchers used satellite imagery of the peak and the 713-square-mile Sagarmatha national park around the mountain as well as long-term meteorological data.

Small glaciers of less than a square kilometre (about 247 acres), are vanishing fastest, registering a 43% decline in surface area since the 1960s, Thakuri said.

Specialists in Kathmandu said the rate of change through the Himalayas was variable. Though clear in places such as Nepal, at the eastern end of the chain, the situation was different in Pakistan and further west, said Arun Shrestha of the International Centre for Integrated Mountain Development in Kathmandu.

"The glaciers are in retreat but rates are different," he said. "It is quite rapid in the east Himalaya but in the west some are advancing while others are in retreat."

Other research suggests the ice of the main Khumbu glacier which flows down from Everest is less thick than it was previously.

The issue of the future of glaciers in the Himalayas is highly controversial. A United Nations report in 2007included a false claim that the Himalayan glaciers would disappear by 2035.

Though all say there is a change, scientists working in the field urge caution over any estimates, saying data is insufficient especially when looking at a small area.

"It is very difficult to scientifically say what are the trends on one particular mountain," Shrestha said.

The impact of climate change on the Himalayas will have consequences across south Asia and beyond. Rivers such as the Indus, Ganges and Brahmaputra depend to some extent on seasonal glacier melt. Countries across the region are already suffering acute water shortages.

"The Himalayan glaciers and ice caps are considered a water tower for Asia since they store and supply water downstream during the dry season," said Thakuri. "Downstream populations are dependent on the melt water for agriculture, drinking and power production."