As the COVID-19 pandemic sweeps across the globe, shutting down cities and crippling economic growth, a sudden decline in pollution has led to speculation that this immense tragedy could be good for the planet.
After all, the canals of Venice are cleaner than in recent memory—so clear that fish are visible in the water—and satellites have revealed a dramatic drop in nitrogen oxide, which contributes to smog, over many metropolitan areas as public life grinds to a halt in an effort to slow the virus's spread.
But while there is no doubt that coronavirus is disrupting our consumption and emissions, according to scientists it is not likely to return many environmental benefits, especially in terms of curbing climate change.
When it comes to drawing conclusions about the effect of the virus on emissions, “people need to just slow down a little bit,” said climate scientist Gavin Schmidt, director of the NASA Goddard Institute for Space Studies in New York, in a call. “Most of the short-lived pollutants that have gone down are associated with transportation. Electricity has not gone away, the internet is still going strong, and power generation is a third of the carbon emissions.”
In other words, greenhouse gas emissions in certain sectors may drop, but they could be counterbalanced by rises elsewhere as the world adjusts to the restrictions associated with COVID-19.
“We are basically using a lot of energy at home right now, much more than before, so really I’m seeing a shift from commercial to residential” emissions, said K. Max Zhang, an air pollution and climate scientist at Cornell University, in a call.
Given all the uncertainties of the present situation, it’s challenging to predict how this shuffling of emission sources will play out in the coming months. A scenario in which the virus is contained within months will look radically different from one in which it takes a year or more to return to “normal” consumption patterns, assuming that is possible.
But even if there are severe long-term disruptions that dramatically cut annual emissions, it would not have a major effect on climate change, Schmidt said.
“The carbon cycle is such that when we add stuff to it, it stays,” he explained. “It’s like a bathtub: The more you put in, the deeper the bath gets.”
“We’re putting more carbon dioxide into the bathtub that is the atmosphere and the surface biosphere and ocean, and that bathtub is filling,” he said. “When I turn the tap down a little, the bathtub still fills.”
For instance, imagine our carbon emissions dropped by a full fifth this year, spiraling down from ten gigatonnes in 2019 to eight gigatonnes in 2020. Given that Earth can only absorb about two gigatonnes a year, that is still six gigatonnes of carbon more than the planet can process.
In fact, COVID-19 lockdowns may even result in a very slight rise in global warming. This is because aerosol pollution, caused by sources such as cars or coal burning, clears out of the atmosphere in a matter of days or weeks.
The quick drop in aerosols explains why many cities in quarantine rapidly experienced a corresponding rise in air quality, though the loss of aerosols may also cause global temperatures to tick up by a small amount. “On average, aerosols cool the planet because they put crap up into the air that’s slightly reflective, which means that less sunlight gets to the ground and more sunlight gets reflected out,” Schmidt said.
That does not mean that aerosol pollution should be seen as a positive by any means, especially considering how harmful smog is to public health—polluted air is estimated to cause millions of premature deaths every year. Moreover, the cooling effect aerosols have is limited to about 0.5°C at most, Schmidt said, which means any warming from the drop in aerosols would be a blip in the larger trend of climate change.
But the differences between carbon emissions and short-lived pollutants does demonstrate that humans place complex pressures on the climate system, which make it hard to predict how public shutdowns and economic downturns will actually tally up on a global scale.
That said, scientists are monitoring all these changes and will be able to use the data to make better informed decisions for the future. The swift reduction in smoggy particulates emitted by the transportation sector, or contrails left by airplanes, will be especially useful because those changes are so much more dramatic and tangible to people.
“What we could look at is if outdoor air quality gets better, which also has health benefits, and how that compares to coronavirus,” Zhang said. “Also, typically we say people spend 80 percent of time indoors, but now it’s more like 100 percent. How is that going to affect human health?”
“Scientists are opportunistic by nature,” he added. “There are a number of past studies that try to take advantage of this kind of episode and try to calibrate models or see how their emissions estimates compare to the reality.”
Schmidt noted that these types of short-term changes are already noticeable to the general public, as well as to scientists, so this could spark people to reassess the compromises we all make between public health and the consumptive excesses of our normal lifestyles.
“You get used to these high levels of pollution,” he said. “This resets everybody’s baselines, and it’s like, 'Oh my God, this is what clean air and water is.'”
“Now, when everything starts back up again—hopefully—it’s going to get dirtier very quickly and people will see that this is much more of a problem than we thought it was,” Schmidt added. “So I think there’s going to be a very interesting resetting of those shifted baselines as we get out of this.”