Dirty snow defrosts Nepal’s mountains

Soot and dust particles from pollution that settle on the Khumbu Glacier makes it melt faster. Photo: EELUM DIXIT.

Fine suspended particles in the air have reached harmful levels, and are reducing the average lifespan of people in urban Nepal by at least two years. Now, scientists have found that pollution is also causing Himalayan glaciers to melt faster than earlier thought.

The role of dust particles is said to be an important driver in reducing the reflectivity of snow and ice, so that they absorb more sunlight and melt faster. And there is more dust blowing into the mountains because of desertification, changing agricultural practices, intense storms, and dust being blown off mountain slopes that have lost snow cover.

‘Because a majority of (Himalayan) snowmelt is generated from seasonal snowpack below 5,000m, dust deposition via elevated aerosol levels can cause a large snow surface albedo reduction and influence snowmelt,’ notes a new study in the science journal Nature. ‘Moreover, the influence of dust on snow darkening is greater than that of black carbon above 4,000m.’

Greenhouse gas buildup in the atmosphere is set to raise global average temperatures by at least 2°C above pre-industrial levels by 2050, and this is still the main reason Nepal’s glaciers are receding and shrinking. But controlling soot particles and reducing dust in the air could slow the process.

The Nature study found that black carbon particles have a larger snow albedo darkening effect than dust because it is darker. But dust contributes more to melting because there is up to 1,000 times more of it than soot.

“Temperatures are increasing faster in the Himalaya, this makes weather conditions more unstable prompting long distance transport of dust and other particles more likely,” explains climate scientist Binod Pokharel. The new study now confirms that the role of dust deposit in melting Himalayan ice is greater than previously thought.

Now that the monsoon is here, people in Kathmandu Valley find it easier to breathe since the air quality index (AQI) is better. But vehicular emissions and brick kiln smoke keep the concentration of suspended soot particles in the air at unhealthy levels.

Dirtier air increases the incidence of chronic obstructive pulmonary disease (COPD), lung cancer, bronchitis, stroke, mental retardation and congenital heart defects. Particles less than 2.5 microns are especially dangerous because they can cross the air-blood barrier in the lung capillaries.

Previous studies on Langtang Glacier showed that while global warming was still the main cause of melting, up to 20% of the defrosting was due to snow darkening because of soot deposition.

The Himalaya is already warming up to 0.7°C faster than the global average, and these suspended particles are increasing the rate of melting. What is new in the research is that dust particles are more responsible than black carbon from pollution simply because there is more of it.

Black carbon in soot from diesel exhaust, thermal power plants, brick kilns and wildfires are transported by wind to glaciers and snowfields, darkening them and making them absorb more sunlight.

Now, climate change is triggering more intense sand and dust storms and prevailing winds during the pre-monsoon and carrying them over long distances to deposit them in the high Himalaya.

But it is not only the origin of dust but the concentration and composition of the pollutant that makes a difference on how it adds to the climate crisis, says meteorologist Namindra Dahal.

For example, suspended particles over cities in India and China have greater inorganic fossil fuel components, while dust being blown in from the Arabian desert have more mineral content. Prevailing winds are from the west for nine months in a year, and blow in sand and soot from West Asia and India to Nepal.

Studies have shown that water in Nepal’s lakes and rivers at higher elevations already have greater concentrations of dust and carbon particles.

“In the past, the air was clean but its composition has changed over the years and that has become a matter of concern due to suspended particles it constitutes, including dust,” explains Dahal. “And all this pollution ultimately ends up in the Himalaya, making it melt even faster.”

At the current rate of melting, and if nothing is done to reduce greenhouse gas emissions, two-thirds of Himalayan ice will be gone by the turn of the century, studies have forecast.

This week, Nepal’s delegation at the UN Climate Conference in Bonn once again urged the developed world to address loss and damage caused by the climate crisis, help the country adapt to extreme weather and prevent glacial lake outburst floods.

However, Nepal must also show a commitment to reducing the increased amount of suspended soot and dust in the air — not just to slow melting of the mountains but also to lessen public health risk. Respiratory problems caused by air pollution alone killed nearly 45,000 people in Nepal in 2019.

Switching to electric public transport and battery-powered two-wheelers would not just clean up the air, but also use surplus hydropower and reduce Nepal’s petroleum import bill.

While much of air pollution is indeed transboundary in nature, but increasingly it is local emissions that worsen the impact on public health and make glaciers melt faster.

Says Namindra Dahal: “Just look at our roads, the dust is killing people and it is killing the mountains. Unless we do our part we have no moral right to demand compensation on the global stage.”

Sonia Awale


Sonia Awale is Executive Editor of Nepali Times where she also serves as the health, science and environment correspondent. She has extensively covered the climate crisis, disaster preparedness, development and public health -- looking at their political and economic interlinkages. Sonia is a graduate of public health, and has a master’s degree in journalism from the University of Hong Kong.