In an interconnected world, the effects of a virus can be found in all sorts of unexpected places. Apparently one of these is the depth of snow lying on the Himalayas. Almost two billion people worldwide depend on meltwater for their water supply, so this is a much more important issue than it may sound, and the changes COVID-19 wrought tell us a lot about the drivers of snowmelt that it affected.

Although India is now experiencing a record-breaking upsurge of COVID-19 cases, its efforts to suppress the first wave were a remarkable success. As well as bringing infections and deaths down at a time when they were rising in many comparable places, the spring lockdown drastically reduced pollution in northern India.

Awful as the circumstances were, Dr Edward Bair of the University of California, Santa Barbara saw an opportunity to expand our knowledge of how pollution affects snowmelt. We know light-absorbing particles (LAPs) from the burning of fossil fuels and wood or dung fires darken snow and ice, causing melting to accelerate, but the exact size of the effect needs work.

In Proceedings of the National Academy of Sciences, Bair and co-authors report that last year’s Himalayan snow was unusually clean. Two forms of analyses of satellite data showed the 2020 snowpack was the cleanest on record; with a 30 percent reduction in LAPs compared to the 20-year average. They estimate this delayed the release of 6.6 cubic kilometers (2.5 cubic miles) of water until unusually late in the season.

The finding might seem obscure, but the consequences are immense. When the Himalayan snows melt too quickly, it can result in floods early in the season followed by insufficient water supplies later on. With 300 million people dependent on the Indus River alone for their drinking water, that’s a problem that easily outweighs many that get far more worldwide attention.

LAPs pose a threat beyond the Himalayas. Although less abundant in the Arctic and Antarctic than on high altitude snow, they still add to climate change-induced polar melting. This in turn causes faster global heating, as less light is reflected back into space. Investigations continue to nail down the size of this effect, and Bair’s work could improve the precision of estimates.

The lockdown-induced reduction in pollution in India has had other benefits as well. Solar panels produced more electricity once they didn’t have to collect light filtered through the gloom. Famously, the clearer air allowed people in Jalandhar to see the Himalayas for the first time in many years. Given air pollution is one of the most common causes of death worldwide, it is almost certain the clearer air also saved a lot of lives, although it may be a long time before we can compare their numbers to those COVID killed directly.