A new United Nations study says global warming is increasing the number of glacial lakes in Nepal and Bhutan, and some could burst their banks with devastating consequences.

Scientists from the U.N. Environment Program say nearly 50 lakes, high in the Himalayas, could burst their banks sending millions of gallons of deadly floodwaters swirling down valleys and putting tens of thousands of lives at risk.

Surendra Shrestha is Asian Coordinator for UNEP's early warning program. More than two billion people depend on the river systems from the Himalayan mountain range, said Surendra Shrestha, Asian Coordinator for UNEP's early warning program. And he says any change in the mountain areas has a direct or indirect affect on the population downstream.

"The meteorological data shows that there is one degree increase in temperature over two decades across the Himalayas. This has resulted in an increase retreat of glaciers. This retreat has meant both the numbers and the size of the lakes is growing," said Mr. Shrestha.

The UNEP study shows that 20 glacial lakes in Nepal and 24 in Bhutan have become potentially dangerous as a result of climate change.

There is no such thing as perfect science, said UNEP's Executive Director Klaus Toepfer. But he says, all indications are that global warming is behind the accelerating melting of glaciers and snowfields in the Himalayas. He notes floods from glacial lakes are not a new phenomenon, but there is evidence that the frequency of such events has risen over the past three decades.

"In this moment where we have to act, there is an overwhelming conviction that climate change happens," said Mr. Toepfer. "It is in line with those explanations that we have an increase of temperature, that we have the melting of the glacier and snowfields, that we have, therefore, also the increase of the glacier lakes and the numbers of those. So, that is a clear signal for this theory."

Mr. Toepfer says there is evidence that any one of the glacial lakes could burst its banks in 5-10 years. And this could have catastrophic results for people and property hundreds of kilometers downstream. The scientists are calling for immediate action. Work already has begun to drain three of the lakes. The scientist say money must be found so that similar preventive measures can be taken with the other lakes.