Scientists say the COVID-19 pandemic slowed the melting of Himalayan glaciers

China's snow clad mountains are seen from the India-China border at Bumla pass from Indian side on Oct. 30, 2006. (AP Photo/Mustafa Quraishi)

Glacial melting in the Himalayan mountains slowed in 2020 as a side effect of economic slowdowns during the COVID-19 pandemic, a new international study has found.

The study, co-authored by scientists from India, Germany and the United Kingdom, was published in the journal Atmospheric Chemistry and Physics on Wednesday.

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Based on global climate simulations, the authors say that returning air pollution to levels to those recorded during the pandemic could protect the Himalayan glaciers, which might otherwise disappear by the end of the century.

"In the model, we were able to show that the decrease in air pollution reduced snowmelt in spring 2020 by 0.5 to 1.5 millimetres per day and thus reduced the runoff meltwater in the year by up to half," said Bernd Heinold, a researcher at the Leibniz Institute for Tropospheric Research (TROPOS) and one of the study's authors, in a media release.

Lockdown measures during the pandemic's early days in 2020 led to a dramatic decrease in passenger and freight transport, industrial emissions and energy consumption. As a result, soot and greenhouse gas pollution in Asia also decreased.

To achieve the same effect long-term — for example, through a switch to clean energy supplies and lower-emission modes of transport — would have major implications for billions of people in South, Central and East Asia, Heinold and his colleagues wrote.

The mountains of the Hindu Kush Himalayas and the highlands of Tibet form the largest snow-covered region outside the poles.

The meltwater from these glaciers feeds rivers in India and China like the Indus, Ganges and Yangtze, which fuel agriculture, hydropower generation and the economies of these countries.

The Himalayan snowmelt in spring also provides half of the annual fresh water for about four billion people in South Asia and East Asia, according to the study. But rising temperatures due to climate change have led to a loss of approximately 40 per cent of the Himalayan glacier area compared to the Little Ice Age in the Middle Ages.

"Model simulations for extreme scenarios show that the melting snow in the Himalayas could cause the glaciers there to disappear by the end of the 21st century," the study reads.

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While higher temperatures caused by climate change are part of the problem, the authors write that light-absorbing soot actually contributes more to the melting of glacial snow than greenhouse gases in the atmosphere. This is because when dark particles like soot absorb light, they heat the air around them.

"The increasing energy demand of densely populated South Asia has greatly increased emissions of greenhouse gases and soot particles in recent decades, leading to increased darkening and melting of snow," the study reads.

However, satellite images show that during the lockdown period between March and May 2020, the snow in the region appeared cleaner, with light-absorbing pollution reduced by about one third. According to the study, this led to a decrease in snowmelt of 25 to 70 mm in 2020, compared to the 20-year average for the months of March to May in the western Himalayas.

"Our results confirm the importance of reducing short-lived climate drivers such as soot and their complementary role in CO2 mitigation," said Ina Tege, a professor at TROPOS and one of the study's co-authors, in a media release.

"Reducing air pollution to similar levels as during the COVID-19 lockdowns in 2020 could protect the Himalayan glaciers, which are otherwise at risk of disappearing by the end of the 21st century."