By all accounts, pollution is down. According to NASA, nitrogen dioxide levels between New York and Washington, DC were down about 30% in March, compared to the average for the last five years. Earlier this year, figures published by CarbonBrief showed that the shutdowns associated with COVID-19 in China led to a 25 percent drop in carbon emissions. Photos from cities like Los Angeles, Moscow and New Delhi show smog-free skies over streets emptied by local shelter-in-place decrees. But in order to make a significant change to the CO2 concentration, those emissions would need to drop by 20 to 30 percent over the course of a year, according to the Scripps team.