Global carbon dioxide emissions fell 8.8% in the first half of this year compared with 2019 (Nat. Commun. 2020, DOI: 10.1038/s41467-020-18922-7). The decrease of 1,551 million metric tons marks the largest year-over-year drop in human emissions of the gas ever observed—larger than during previous economic crises.
The Carbon Monitor study, led by Tsinghua University’s Zhu Liu, used daily information on electricity production, traffic, flights, fuel consumption, and the weather. The biggest and most persistent moves were in emissions related to transportation. Travel and business restrictions designed to slow the spread of COVID-19 resulted in far lower CO2 emissions from ground transportation—particularly in April and May, which saw declines of 38.6% and 32.6%, respectively—compared with the same periods in 2019. By July, transportation emissions were still 13% lower compared to the same month in 2019.
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January through March were warmer than the same period in 2019, so emissions from power generation would have fallen during those months even without the pandemic. But the Carbon Monitor analysis shows that COVID-19 shutdowns account for 85% of the power sector’s emissions decline from January to March.
Tallying CO2 emissions is typically a protracted process that doesn’t capture daily or even monthly activity, says Ronald Cohen, a chemist at the University of California, Berkeley. Cohen, who was not involved with the Carbon Monitor study, says the unusual emissions this year are pushing scientists to hone their tools to track greenhouse gases and pollution closer to real time. In coming years, quarterly greenhouse gas emissions could help agencies ensure that their country or region is on target to achieve reductions.