By modeling where the trend line was heading for several key greenhouse gases, and then comparing said trend line to what actually happened after COVID19 forced the world to shutter major cities, NASA's study suggests humanity is responsible for global warming (even if they don't just say it.)
Wuhan, China was the first municipality reporting an outbreak of COVID-19. It was also the first to show reduced nitrogen dioxide emissions—60% lower than simulated values expected. A 60% decrease in Milan and a 45% decrease in New York followed shortly, as their local restrictions went into effect.
"You could, at times, even see the decrease in nitrogen dioxide before the official policies went into place," said co-author Emma Knowland with USRA at Goddard's GMAO. "People were probably reducing their transit because the talk of the COVID-19 threat was already happening before we were actually told to shut down." Once restrictions were eased, the decreases in nitrogen dioxide lessened, but remained below expected "business as usual" values.
Keller compared his estimates of the nitrogen dioxide decreases to reported economic numbers, namely, the gross domestic products, of the nations included in the study. According to Keller, they lined up shockingly well. "We would expect them to be somewhat related because nitrogen dioxide is so closely linked to economic activities, like people who travel and factories running," he said. "It looks like our data captures this very well."