Bengaluru Jun 20, 2019, (Research Matters):
Melting of glaciers in the Himalayas doubled in the last four decades, reveals spy satellite data
“I’m going, I’m going, I’m gone”—these lines from Bob Dylan’s song Going, Going, Gone could soon be the anthem of our planet’s glaciers! With alarming news reports of melting glaciers coming from the Himalayas, the Alps and everywhere, the Anthropocene epoch, dominated by climate change and global warming, is here. Now, a new study by researchers at Columbia University and the University of Utah, USA, has revealed that glaciers in the Himalayas are receding twice as fast now than they were at the end of the previous century.
The study, published in the journal Science Advances, investigated glaciers along the 2000 kilometers stretch from Spiti-Lahaul in India to Bhutan. It included glaciers that accumulate snow in the winter, present in the western Himalayas and those that gather snow in the summer, located in the eastern Himalayas. It excluded abnormally surging glaciers in the Karakoram and Kunlun region. In all, the study analysed the changes in the mass of 650 glaciers, accounting for 55% of the ice volume in the region.
The researchers collected satellite data about these glaciers from two time-periods—1975-2000 and 2000-2016. Interestingly, the data from 1975-2000 came from the declassified photos taken by the spy satellite KH-9 Hexagon, launched by US agencies during the Cold War period. KH-9 Hexagon has collected thousands of photographs from around the world to aid the agencies in surveillance. The second set of data came from ASTER, a remote sensing device launched by Japan.
The study estimates that by 2000, the total ice mass of the region had reduced to 87% of what was seen in 1975, and by 2016, this number further dwindled to 72%. During the sixteen years between 2000-2016, many of the glaciers lost ice twice as fast, with some regions like Spiti-Lahaul losing about thrice of their ice.
“Our results indicate that glaciers across the Himalayas experienced significant ice loss over the past 40 years, with the average rate of ice loss twice as rapid in the 21st century compared to the end of the 20th century”, say the researchers about their findings.
Although more studies are needed to understand the factors contributing to this massive loss, the researchers believe that an increase in global temperature is the likely culprit. For the ice loss observed, they estimate a temperature rise between 0.4oC to 1.4oC during 2000-2016 as compared to 1975-2000. These estimates conform with meteorological measurements of an increase in 1oC in the region. It is probable that the increased black carbon emissions in the area could be driving the rise in temperatures.
Interestingly, the debris in these mountains, which include stones and pebbles, could be playing a role in the thawing of the glaciers, suggest the researchers. The study found that the average rate of ice loss for debris-covered glaciers was slower than clean-ice glaciers at low elevations. However, at mid-range altitudes, debris-covered glaciers melted faster as the debris cover is sparse.
The glacial waters of the Himalayas are vital for ecology, agriculture and hydropower and any change in the rate of glacial melting could lead to flash floods and insufficient water in the rivers, affecting societies and policies. Hence, understanding the sensitivity and response of these glaciers to the changes in climate is vital to brace for this challenge. The findings of the study, which looks at Himalayan-wide historical record of ice loss, provide some direction in this regard.