Glaciers in the Himalayas have shrunk by as much as a fifth in the last 30 years, scientists have claimed in the first authoritative confirmation of the impact of climate change on the region.

The findings of reports published by the International Centre for Integrated Mountain Development (ICIMOD) headquartered in Kathmandu, show Nepal's glaciers have shrunk by 21 per cent and Bhutan's by 22 per cent over 30 years.

"These reports provide a new baseline and location- specific information for understanding climate change in one of the most vulnerable ecosystems in the world," Rajendra Pachauri, chairman of the Intergovernmental Panel on Climate Change, said.

A three-year Sweden-funded research project led by ICIMOD showed 10 glaciers surveyed in the region all are shrinking, with a significant loss of ice between 2002 and 2005.

The reports, launched by ICIMOD on Sunday at the UN climate talks in Durban, South Africa, form the most comprehensive ever assessment of the extent of melting Himalayas.

The reports follow a claims made by scientists in 2007 that the region's glaciers would be gone by 2035.

The study also found a significant reduction in snow cover across the region in the last decade.

The effects of climate change could be devastating, as the Himalayan region provides food and energy for 1.3 billion people living in downstream river basins, warn scientists.

"The Hindu Kush-Himalayan region is like a gentle giant. While physically imposing, it is one of the most ecologically sensitive areas in the world," said David Molden, director general at ICIMOD.

"Up until now, there has been complete uncertainty on the numbers and area of glaciers and the present status of their environmental conditions in the region, said Basanta Shrestha from ICIMOD.