Drop in air pollution in India during 2020 nationwide lockdown slowed snow melting in Himalayas, finds study

Snow & ice melt reduced by more than 27 million tonnes compared to 2019

By Zumbish
Published: Thursday 06 July 2023
Dust aerosols from the Indian Peninsula has a strong physical connection with the darkening of snow and ice on the Tibetan Plateau. Photo: iStock

A decrease in air pollution in India during the COVID-19 pandemic slowed the melting of snow in the Himalayas, according to a new study. 

As business came to a halt, particulate pollution reduced and, as a result, more than 27 million tonnes of snow and ice were saved from melting compared to 2019, the report published in the journal PNAS Nexus showed. 

The researchers used satellite data to track the impact on snowmelt during the two-month nationwide lockdown in India in the spring of 2020. 

The study assessed that changes in Himalayan RFSLAPs (influence of human activities on radiative forcing on snow) is linked to Indian lockdown. Differences between the RFSLAPs in 2020 and the average from 2017-2019 over the Tibetan Plateau  was calculated. 

The differences during the lockdown period (from April to May) and differences during the pre-lockdown period (from January to March) were kept in consideration.

As an important emitter of light absorbing particles (LAP), human activity largely controls the variation of LAP concentrations in ice and snow, the report noted. “Dust aerosols from the Indian Peninsula have been reported to have a strong physical connection with the darkening of snow and ice on the Tibetan Plateau.”  

Assessing RFSLAPs is essential for providing valuable guidance for effective mitigation strategies. However, LAP variations reflect a complex mixture of anthropogenic emissions and natural environmental factors and are very sensitive to meteorological conditions, the researchers wrote in the report.  

For example, changes in winds can affect LAP transport and deposition, and temperature and snowfall are closely related to the accumulation of LAPs in the snow, the scientists explained.

How did the impact take place? 

The COVID-19 pandemic has created a unique natural experiment for revealing and answering the long-standing question of how reductions in human activities can affect air pollution. 

To cope with the COVID-19 pandemic, the Indian government implemented a national lockdown from March 25-May 31, 2020. This led to an unprecedented reduction in economic and transportation activities and pollution levels. 

Aerosol optical depth values dropped sharply and air quality improved across the country. LAP concentrations over the Indus Basin have also decreased greatly. Such a reduction in LAPs over India might have meant a substantial drop in pollution transported to the Tibetan Plateau.

This study provides evidence that reductions in anthropogenic emissions are helpful to decrease snow and glacial melt. It also offers evidence that the reduction in transboundary LAPs has a remarkable beneficial effect on the reduction of the Himalayan snow and ice melt. It provides an opportunity for targeted emission mitigation to constrain the timing and magnitude of future glacier retreat. 

Mineral dust transported from the Thar Desert by westerly winds deeply influences RFSLAPs and the rate of ice and snow melting in the western and central Himalayas. 

Thus, reduction in deforestation and overexploitation of the Indus River Basin may help improve the ecological environments around the Thar Desert, and further decrease mineral dust transport to melt ice and snow on the Tibetan Plateau.

Furthermore, continued use of fossil fuels in the future would increase ice and snow melt by increasing the LAPs, in addition to leading to sustained global warming.

With rising temperatures, ice and snow over the Himalayas have been melting at an accelerating, alarming rate in recent decades, the researchers wrote. “At the current pace of warming, up to 70 per cent of Himalayan glaciers could be lost this century.” 

Reducing particulate pollution in South Asia, they said, could help preserve what snow and ice remain.

Overall, these results suggest that the anomalies in Tibetan Plateau RFSLAPs were tied to absorbing aerosol optical depth (AAOD) over the Indian Peninsula. “Notably, India is a major emitter of anthropogenic LAPs over the Indian Peninsula, but the reduction in AAOD and RFSLAPs during the lockdown cannot be entirely explained by a decrease in human activities in India as the meteorological conditions and the nonanthropogenic LAPs coming from multiple countries are also important factors for the changes in AAOD and RFSLAPs.”

Over a billion people in South Asia depend on the steady melt of snow and ice in the Himalayas through the spring and summer for fresh water. But particulate pollution from cars, trucks, factories and power plants in South Asia disperse over the mountain range, disrupting this process. 

Soot darkens snow and ice, causing it to absorb more of the sun’s energy and melt faster.

Experts on air pollution in India provided further explanation in the wake of the study observations.

"It is known that black carbon falls onto snow and ice and changes the overall reflectivity of those surfaces, making them melt faster. Therefore, any reduction in its concentration through augmenting clean fuel supply, better combustion system and overall air pollution control measures is bound to help,” said Vivek Chattopadhyay, senior programme manager, Clean Air Programme, Centre for Science and Environment.

However, at the same time, scientists need to highlight the effects of both overall impacts of rising temperatures due to global warming as well as localised effects of black carbon to emphasise the fact that air quality improvement and greenhouse gas emissions reduction must become a two pronged strategy, he added.

Also, black carbon reduction measures will have positive health benefits on populations too, according to the expert. “Lockdown was perhaps a once-in-a-century opportunity to observe what clean skies look like and, therefore, its positive messages should continue to drive us towards continuing clean air measures which can have many benefits.”

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