Experts from the U.N. Environment Programme (UNEP) and the World Glacier Monitoring Service (WGMS) said while there has been excellent monitoring of glacial trends in Europe and North America, ice fields in Central Asia and the tropics have been largely overlooked.

This is a major concern given that shrinking and thinning glaciers -- a phenomenon linked to climate change -- could put freshwater supplies at risk for hundreds of millions of people, authors Peter Gilruth and Wilfried Haeberli said.

"Data gaps exist in some vulnerable parts of the globe undermining the ability to provide precise early warning for countries and populations at risk," they concluded.

Their report, released at a meeting of the Intergovernmental Panel on Climate Change (IPCC), a U.N. scientific body, called for more investment in high-tech monitoring tools for Central Asia, South America, East Africa and in Papua New Guinea.

The IPCC has said global warming, stoked by the burning of fossil fuels such as oil, will trigger more droughts, floods, heatwaves, and severe storms, and cause sea levels to rise as glaciers and polar ice caps melt.

According to the UNEP and WGMS study, the average melting rate of mountain glaciers has doubled since the turn of the millennium, with record losses seen in 2006 at several sites.

If governments fail to agree to deep emissions cuts when they negotiate a successor deal to the Kyoto Protocol next year in Copenhagen, the authors said it was possible that glaciers may disappear completely from many mountain ranges this century.