Amid controversy and debate over the precise impact of global warming on the Himalayas, glaciologists analysed a massive cache of data on the mountain range and have concluded that it lost 13 per cent of its glaciers in just four decades.

Approximately 443 billion tonnes (Gt) of glacier ice was lost in this timeframe, says a new research paper published in Current Science. It estimates the total glacial water stored in the Indian Himalaya to be around 4,000 Gt.

“This loss is significant considering the amount of water stored in the glaciers of the Indian Himalayas” say authors Anil V. Kulkarni and Yogesh Karyakarte of the Divecha Centre for Climate Change at the Indian Institute of Science (IISc).

The scientists reviewed information on 11,000 sq km of Himalayan glaciers — from existing field investigations, satellite imagery, inventories of the Geological Survey of India, scientific papers and maps — and conclude that in fact “most of the Himalayan glaciers are retreating.”

The rate of retreat however varies from glacier to glacier, ranging from a few metres to almost 61 m/year.

Several predictions have been made about the impact of global warming on the Himalayas, many of which have been speculative, not least because of gaps in data, says the paper.

One such assessment, it points out, was this (controversial) statement made by the Intergovernmental Panel on Climate Change (IPCC) in 2007: “If the present rate [of glacial retreat] continues, the likelihood of them disappearing by year 2035 and perhaps sooner is very high if the earth keeps warming at the current rate.”

While IPCC’s hypothesis was erroneous and alarmist, the fact that glaciers are indeed being lost is in no doubt, Prof Kulkarni told The Hindu. “What we find is that Karakoram is the only stable range. The others are retreating at different rates.” The investigation also finds that the rate of glacial loss in the Himalayas has accelerated over the decades: from around 9 Gt/year in 1975-85 to 20 Gt/year in 2000-2010. Glaciers are retreating faster in Western Himalaya than in Sikkim, it adds.

Existing research on the Himalayas, said Prof Kulkarni, tends to focus on specific segments and not the chain in its entirety. Studies on glacial retreat also often overlook other key indicators of glacial loss such as the decrease in the depth of glaciers, which is more difficult to calculate. “This has obviously created considerable confusion among the scientific community and the public over the extent of glacial loss. The purpose of our study is to present a larger picture of the Himalayas as a whole and bring about a cohesive picture.” The paper cautions that the best estimates of globally averaged surface air warming vary between 1.8° and 4.0°C and that “this would have profound effect on the Himalayan glaciers.”