Richard A Lovett
Scientists studying satellite images of the Earth have identified changes linked to COVID-19 lockdowns that may shed light on how the environment responds to massive reductions in air and water pollution.
“These changes are really dramatic,” Ned Bair, a snow hydrologist at the University of California, Santa Barbara, told this week’s virtual meeting of the American Geophysical Union.
“We are seeing changes [which last occurred] so long ago that we didn’t have a satellite record,” he said. “It’s a glimpse of how a cleaner world could look.”
Some of these changes may even provide clues to how a cleaner environment could, at least in some areas, help offset the ravages of global warming, even apart from their effect on planet-warming greenhouse gas emissions.
One of these places is southern Asia.
The fact that reduced travel and industrial activities during COVID-19 lockdown cleaned up the air there is well known. “There are lots of tweets and social media on how the Himalaya were visible from Delhi for the first time in 30 years,” Bair says.
But the cleaner air, he realised, should also have produced cleaner snow in the mountains.
To confirm this, he turned to the headwaters of the Indus River, which annually produces 95 cubic kilometres of snowmelt to help supply water to 300 million people.
Normally, he says, that snow can get pretty dirty, thanks to particles deposited by polluted air. But during the lockdown, satellite images showed it to be notably brighter than normal – meaning it was cleaner.
Cleaner snow, of course, means cleaner water. But that’s not its primary benefit. Because it’s brighter, it absorbs less sunlight and melts more slowly.
That’s critical for people downstream, Bair says, because it improves the timing of their water supply, particularly in areas that don’t have dams to capture early-season water and parcel it out for later use. In parts of Afghanistan (whose rivers are fed by snow in the same mountains), streams can even run dry by September. “There’s no water,” he says.
One of the concerns about global warming is that it’s expected to exacerbate this problem by shifting the start of the melt earlier into the spring and accelerating the time of final “melt-out”.
Cleaner snow has the opposite effect: later melt onset and delayed melt-out.
Global climate change isn’t the only COVID-related impact geophysicists are studying from space. Nima Pahlevan, a remote-sensing scientist from NASA’s Goddard Space Flight Center, took advantage of COVID to study the impact of dramatic reductions in sewage discharges into urban waterways, using satellite measurements to reveal a substantial improvement in water quality near New York City’s Manhattan Island when lockdowns required 2.1 million commuters to stay at home.
Such research isn’t just of academic interest, says Timothy Newman, program coordinator of the National Land Imaging Program at the US Geological Survey.
Space-based observations have only been around for about 50 years, he says, but increasingly there’s a push to use them to project the impacts of future events, whether they be environmental policy changes, future pandemics, or hurricanes.
Such projections are never perfect, but the more we can extend our knowledge to understand what is happening in unusual events like the COVID-19 lockdowns, the better we can do at anticipating the effects of whatever might come next.
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