Carbon dioxide emissions plateaued in 2019, even as the world’s economy expanded, mostly because of declining coal use for power generation and mild weather in many developed nations. But as countries have restricted activity because of the novel coronavirus, the economy has contracted substantially. At the time of this writing, for example, some 40 million US citizens have applied for unemployment benefits. Now Corinne Le Quéré of the University of East Anglia and her colleagues have quantified the pandemic’s effect on CO2 emissions. In early April 2020, daily global CO2 emissions decreased to the same levels measured in 2006.
The scientific community lacks a real-time global observing system for CO2, so Le Quéré and her coauthors estimated emissions based on the slowdown in activity by economic sector. They then extrapolated the observations using an index of the stringency of confinement that each country has experienced during the pandemic. (The CO2 emission data that’s paired with the activity observations comes from the Global Carbon Project, the US Energy Information Administration, and national statistics from China.) The analysis, summarized in the graphs below, shows that CO2 emissions decreased some 17% by April 2020 compared with 2019. That reduction is roughly equal in magnitude to the seasonal change in emissions that the Northern Hemisphere experiences as higher energy use during winter gives way to lower energy demand in summer.
How long the fall in CO2 emissions will persist depends on how much longer countries decide to keep social distancing and shelter-in-place guidelines in effect. If most countries resume business as usual by mid-June, emissions would decrease 4.2% overall for the year; 5.3% if economic activity resumes in late July; and 7.5% if some restrictions continue for the remainder of 2020. Coincidentally, CO2 emission reductions of 4.2–7.5% are about the rate of decrease required to meet the Paris Agreement’s goal to limit the global temperature increase to no more than 1.5 °C. (C. Le Quéré et al., Nat. Clim. Change, 2020, doi:10.1038/s41558-020-0797-x.)