A locked-down pandemic-struck world cut its carbon dioxide emissions this year by 7%, the biggest drop ever, new preliminary figures show. The Global Carbon Project, an authoritative group of dozens of international scientists who track emissions, calculated that the world will have put 37 billion U.S. tons (34 billion metric tons) of carbon dioxide in the air in 2020. That’s down from 40.1 billion US tons (36.4 billion metric tons) in 2019, according a study published Thursday in the journal Earth System Science Data. Scientists say this drop is chiefly because people are staying home, travelling less by car and plane, and that emissions are expected to jump back up after the pandemic ends. Ground transportation makes up about one-fifth of emissions of carbon dioxide, the chief man-made heat-trapping gas.