It’s been one of the few slivers of hope as we’ve trudged through the Covid-19 catastrophe: As industries shuttered and we all sheltered in place, we’ve stopped spewing so much planet-warming gas. One analysis by the climate group Carbon Brief in April calculated that emissions could fall by 5.5 percent this year. That seems like a tiny tally until you consider that until 2020, emissions had been steadily ticking up year after year, and that the 2008 economic collapse brought about only a 3 percent reduction.
I am here to snatch that sliver of hope away from you—and potentially replace it with a new sliver of hope. Writing today in the journal Nature Climate Change, an international team of scientists calculates that the coronavirus lockdown may only cool the planet by about 0.01 degrees Celsius by the year 2030. (The rough math is that 1 degree Celsius equals 1.8 degrees Fahrenheit.) But. They also argue that if humanity would aggressively fund renewables in the aftermath of the pandemic, we could avoid an overall increase of 0.3 degrees by 2050—that’s 0.6 degrees Fahrenheit. That could keep the planet within 1.5 degrees Celsius (2.7 degrees Fahrenheit) of warming from pre-industrial levels, the goal set out in the Paris Climate Agreement.
To quantify the change in emissions during shelter-in-place, the researchers looked at Google’s and Apple’s anonymized mobility data from cell phones. As a proxy for human activity, these figures showed how the emissions of greenhouse gases like CO2 and NOx (aka nitrogen oxides, which trail from cars) from 123 countries changed between February and June, 2020. The team found that traffic patterns would indicate that these and other gases fell from between 10 and 30 percent globally as civilization locked down.
But why look at mobility data, and not just train a satellite on the planet to measure CO2? The problem is that carbon dioxide is a very long-lived gas in the atmosphere, persisting for hundreds of years. (Compare that to methane, which is a more potent greenhouse gas, but disappears after about a decade.) These few months of lockdown have been but a blip in the atmospheric timescale of CO2. “It takes a very long time for these changes in carbon dioxide to change the concentrations,” says Piers Forster, director of the Priestley International Centre for Climate at the University of Leeds and a lead author on the new paper. (He actually co-designed the study with his daughter, Harriet Forster, a day school student. They began working on the research when her A levels were canceled because of Covid-19.)
In a frustrating bit of irony, the reduction in emissions during the pandemic has in a way warmed the planet. While CO2 emissions have fallen, so too have sulfur dioxide (SO2) emissions from the burning of coal, as heavy industries reduced their energy use. This air pollution from power plants normally forms aerosols in the atmosphere, which bounces some of the sun's energy back into space. But once industry dropped off, so did the aerosols, “and that causes a reduction in the amount of sunlight being reflected, and that causes an increase in the temperature” at the surface of Earth, says Forster. “The really first effect of reducing the emissions is in fact an increase, we think, in the surface temperature.”
That warming, combined with the fact that CO2 lasts so darn long in the atmosphere, means that the lockdown will lead to a minuscule net amount of cooling by 2030. “The temperature change from this lockdown will only be one hundredth of a degree,” says Harriet Forster. “But the point is what we can do recovering from this. If we invest in green energy, we could really improve our chances of reaching the 1.5 degree target.”