Getting at these figures takes a whole lot of digging through data, because scientists can’t just train a satellite at the planet and get CO2 emissions in real-time. “Because CO2 stays in the atmosphere a long, long time, even though we had a massive change in emissions, that did not affect the stock of CO2 in the atmosphere very much,” says climate scientist Corinne Le Quéré of the University of East Anglia, lead author on the paper. “It's small compared to what we've put in the atmosphere for decades.”
Got a coronavirus-related news tip? Send it to us at [email protected] .Plus, that CO2 signal is muddied by Earth’s natural processes, like trees sucking in the gas and expelling oxygen. And with a satellite, you can’t measure levels of a gas at the surface rather than what you would find a mile in the air. “We’re measuring a whole column amount of CO2,” says Northern Arizona University climate scientist Kevin Gurney, who models emissions but wasn’t involved in this new work. “It’s not a flux at the surface. It’s just a big cross-section of the number of molecules in the atmosphere.”
So Le Quéré and her colleagues waded through mountains of reported data instead. They looked at statistics about car traffic, electricity usage, airline flights, and manufacturing, building a global picture of how the pandemic has cut emissions. Each sector comes with its own unique dynamics: Air traffic has of course plummeted, but that industry only accounts for 3 percent of global carbon dioxide emissions in a normal year.
Each country’s emissions patterns are unique, too. For example, China’s economy is heavy on manufacturing, which shut down early as the virus took hold. China has seen carbon dioxide emissions drop by 242 megatons, compared to 207 megatons in the US, and 123 throughout Europe. Activity in China’s coal production fell between 30 and 40 percent—mirrored by a similarly-sized drop in the US, but in steel production. The US also nurtures a big service industry that allows people to work remotely, in a sense shifting the electricity usage from offices into homes. Residential energy use also ticked up a bit in the UK as people sheltered in place. (But to make the energy calculus even more complex, when people work from home, that also means they’re not sitting in traffic generating more tailpipe CO2.)
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All told, the decrease in global emissions during the pandemic has been precipitous. But in the grand scheme of things, emissions have been increasing so reliably since … well, pretty much the beginning of the Industrial Revolution, that so far Covid-19 is but a blip on that upward trajectory. “The biggest decrease we had in one day takes us back only to 2006 levels,” says Le Quéré. “So this is really showing just how much emissions are increasing through time every year. This incredible drop in emissions only takes us back 14 years.”