NEW DELHI: Most glaciers on the Tibetan plateau and around it are rapidly melting says the latest study based on 30 years of satellite data and also actual measurements. This upturns results of a study published earlier this year based on satellite measurements over seven years which said that Tibetan glaciers are growing.

The most recent study was done by Chinese glaciologists and is published in the latest issue of scientific journal Nature Climate Change.

The Tibetan plateau and the mountain ranges radiating from it - the Himalayas, the Karakoram, the Pamir and the Qilian - contain 100,000 square kilometres of glaciers that supply water to about 1.4 billion people in Asia through huge river systems like the Ganga, Brahmaputra, Indus, Mekong, Yangtze etc. This gigantic collection of freshwater - mostly ice - has led many to call the region the Third Pole of the Earth. Global warming and related climate changes may cause reduction of water in this gigantic lifeline affecting billions.

The Chinese scientists analysed satellite measurements of the lengths and surface areas of about 7,100 glaciers. They also physically measured 15 glaciers for decades in order to confirm the net changes taking place. They found that the majority of the glaciers have been shrinking rapidly across the studied area in the past 30 years, and at accelerating rates.

So what explains the fact that other studies have come up with different results? According to this study, there is a large variation in different parts of the Third Pole. For instance, glaciers in the Himalayas are retreating faster on average than those in the Karakoram and the Pamir. And the reason for this was discovered in an unexpected factor - wind.

Studying climate records of the entire region, the scientists found that changes in the glaciers depend on whether the ice is under the influence of the Indian monsoon or the westerlies, the winds blowing in from the West, that is, from Europe.

In the Karakoram and the Pamir plateau, the westerlies are dominant and the glaciers grow by accumulating winter snow. So, they are less affected by warming because temperatures in winter are still below zero, says the study. In the eastern and central Himalayas it snows mainly during monsoon and a slight increase in summer temperatures can affect glaciers drastically.

As the Indian monsoon has grown weaker in the past few decades, and the westerlies have gained strength, the western part of the region has seen glacier increases while the central and Eastern part - mainly the Himalayas and Tibet - have lost ice from their glaciers.

The study also found that there has been a 26% increase in the area covered by glacial lakes, formed from melting glaciers, in the region since the 1970s. The earlier GRACE study which announced that glaciers were increasing in size could have been misled by these lakes says the present study because it was measuring gravity pull by satellite and would not have been able to distinguish between water and ice.

John Wahr, a remote-sensing expert at the University of Colorado Boulder and lead author of the GRACE study, was quoted by Nature as concedinf that the criticism is valid.