What would a pandemic-free 2020 have looked like? A new model created by NASA aimed to answer that question, revealing the dramatic effects that the coronavirus lockdown had on Earth's atmosphere.
Researchers at NASA created a computer-generated model mapping out how the year 2020 would have played out without a global pandemic. The maps reveal a shocking truth: Global nitrogen dioxide levels were nearly 20 percent lower this year than they might otherwise have been.
It is a stark demonstration of just how great an affect humanity has on the balance of greenhouse gases in our atmosphere.
Researchers presented the model this week at the 2020 International Conference for High Performance Computing, Networking, Storage, and Analysis.
Since government-mandated lockdowns began across the globe earlier this year, satellites have measured a significant drop in nitrogen dioxide levels across the world. Satellite imagery collected by the European Space Agency (ESA) in April revealed a 45-50 percent drop in nitrogen dioxide levels across Europe. And satellite data collected by NASA in March 2020 showed a 30 percent drop in nitrogen dioxide levels compared to the average levels recorded from March 2015 through March 2019 across the Northeast United States.
Nitrogen dioxide is one of the most abundant greenhouse gas pollutants, and is used as a measure of air pollution.
The scientists behind the new models had a suspicion that with lockdowns, human activity would slow, and, in turn, greenhouse gas emissions would drop. But they needed to prove the hypothesis.
“We all knew the lockdowns were going to have an impact on air quality,” Christoph Keller, a scientist at NASA’s Goddard Space Flight Center and co-author of the new research, says.
“It was also soon clear that it was going to be difficult to quantify how much of that change is related to the lockdown measures, versus general seasonality or variability in pollution," he explains.
Comparing nitrogen dioxide levels of the year 2020 with previous years like 2019 and 2018 doesn't actually tell scientists much about how the coronavirus-related restrictions affected global air pollution. Regular variations in weather and atmospheric circulation change the make-up and chemistry of Earth’s atmosphere, so no two years are exactly alike.
So rather than compare the year 2020 with a previous year, the researchers compared 2020 with a version of itself — a 2020 without the spread of a global pandemic.
The NASA Center for Climate Simulation created an alternate reality for the year 2020, where human activity had not been completely altered due to lockdown restrictions.
The researchers then compared the nitrogen dioxide levels simulated in the model with the levels measured by satellites throughout this year across 46 countries.
They found an average drop of nearly 20 percent worldwide, with 50 of the 61 cities analyzed showing nitrogen dioxide reductions between 20-50 percent compared to what might have happened in a pandemic-free 2020.
Wuhan, China showed a 60 percent reduction in nitrogen dioxide levels, so did Milan, Italy, while New York City had a 45 percent decrease.
The new model illustrates just how much human activity affects air pollution levels worldwide.
“In some ways I was surprised by how much it dropped,” Keller said.
“Many countries have already done a very good job in lowering their nitrogen dioxide concentrations over the last decades due to clean air regulations, but what our results clearly show is that there is still a significant human behavior-driven contribution.”