"Glacial darkening" is where deep purple, bulbous algae sprout on a layer of naturally occurring dust mixed with soot from air pollution and forest fires.

Their presence has been confirmed for decades but as temperatures rise, more algae are thriving on the ice surface, staining glaciers the world over.

Scientists differ on how much additional melting this will cause but four scientists who are studying glaciers told Reuters it would exceed what was accounted for in current projections, including those in a landmark UN report released in September.

"Glaciers have algae growths often feeding on carbon deposits so that is further darkening the ice," said John Pomeroy, a professor at Canada's University of Saskatchewan, on the sidelines of a "High Mountain Summit" in Geneva this week.

"These are not currently considered in our models for glacier melt and almost certainly will accelerate it further than our estimates currently show."

Policy-makers and experts are convening at the UN's World Meteorological Organisation this week to discuss how to mitigate risks such as flash floods and droughts in mountain areas caused by global warming.

A study released last month by the UN-backed Intergovernmental Panel on Climate Change (IPCC) predicted that glaciers in polar and high mountain regions will likely lose "substantial mass" by the end of the century, ultimately raising sea levels.

The host of the meeting, Switzerland, has already lost 500 glaciers since the start of the last century and it could lose 90 per cent of the remaining 4000 if nothing is done to reduce greenhouse gas emissions by 2100, Home Affairs Minister Alain Berset told participants.

Australian Associated Press