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Wednesday, 26 June 2019

Climate change eats the glaciers of the Himalayas

Changri Nup, a glacier covered with debris in the Everest region

Since 2000 the glaciers of the Himalayas have lost almost half a meter of ice a year, twice as much as in the period from 1975 to 2000. The study, which has combined the images - now declassified - of a US spy satellite during the Cold War with current images from NASA, indicates that glaciers have lost a quarter of their mass in the last 40 years.

The loss of ice has accelerated since the year 2000 in the glaciers of the Himalayas, mountains considered the "third pole" by holding some 600,000 million tons of ice. Each year about half a meter of ice melts due to the increase in temperatures, which have increased by 1 ° C in some places.

A study, published today in the journal Science Advances , presents this image of the Himalayas after analyzing the changes of the last 40 years in the region thanks to the images obtained by the American spy satellite KH-9 Hexagon , known as Big Bird, made during the Cold War and declassified in 2011; and others, more current, provided by NASA in India, China, Nepal and Bhutan.

"This is the clearest picture to date of how quickly the glaciers in the Himalayas are melting in this time frame, and for what reasons," says Joshua Maurer , first author of the work and researcher at the Lamont-Doherty Earth Observatory. of the Columbia University (EE UU).

The team of scientists analyzed 650 Himalayan glaciers , which represent 55% of the total ice volume of the region, in an area of ​​2,000 kilometers from west to east, and estimated that, of the mass of total ice present in the area in 1975, 87% remained in 2000 and 72% in 2016. That is to say, that the glaciers of the Himalayas would have lost a quarter of their mass in the last four decades.

The results were obtained thanks to the creation of an automated system that converted the images of the spy tape into 3D models . These showed altitude alterations over time. The data was then compared to images obtained from 2000 on more sophisticated satellites, which directly transmit changes in altitude.

Image obtained by a US spy satellite on the Khumbu region from the declassified program HEXAGON KH-9. This is what the glaciers surrounding Everest looked like in 1976.

The consequences of thawing

According to the study, from 1975 to 2000, glaciers in the region lost an average of about 25 cm of ice per year due to a slight rise in temperatures. The trend intensified in the 1990s until, in the 2000s, the loss of ice accelerated and reached 50 cm per year .

The melting of recent years would represent an annual loss of 8,000 million tons of water, the equivalent of 3.2 million Olympic swimming pools. But the glaciers do not melt evenly. The scientists observed that the melting occurs mainly at lower altitudes , where in some areas up to five meters of ice loss per year have been recorded.

The meltdown could affect some 800 million people, who depend on seasonal runoff for irrigation, hydropower and drinking water. Currently, significant runoff is occurring, but as the glaciers lose mass it will be reduced in the coming decades. This will cause shortage of water.

In addition to the increase in temperatures, the work suggests that changes in precipitation , which decreases in some areas and increases in others, could be influencing the area.

The scientists add another factor: the increasing burning, by Asian countries, of fossil fuels and biomass that send soot into the atmosphere. Much of this ash lands on snowy glacial surfaces, where it absorbs solar energy and accelerates thawing.


 JM Maurer et al.
"Acceleration of ice loss across the Himalayas over the past 40 years"
Science Advances June 19, 2019

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