Stay-at-home orders have curbed the spread of COVID-19 in many places. Those limits on travel also have had an environmental benefit: cleaner air.
The coronavirus lock-downs grounded planes. They also cut traffic and changed peoples’ patterns of energy use. One impact was a sharp drop in daily global emissions of greenhouse gases. Chief among these is carbon dioxide, or CO2. By early April, releases of that gas had dropped 17 percent from the 2019 average of about 100 million metric tons per day. They were now some 83 million metric tons per day. Researchers shared their finding May 19 in Nature Climate Change.
Tallying up this impact proved tricky. Climate scientists had to be clever to come up with a real-time number. Most data on emissions are collected and reported once a year (not day by day or even month by month).
Corinne Le Quéré of the University of East Anglia in Norwich, England, and her colleagues used different daily data as their starting point. These included data on traffic congestion. They also used data from smart meters in homes and other measures of energy use. From this, they estimated CO2 releases for 69 countries. Scientists sometimes refer to such a value as a nation’s carbon footprint.
Next, the researchers created a “confinement index.” This accounted for how strict stay-at-home policies had been from place to place. They used this to calculate how this should have affected that carbon footprint.
During the strictest pandemic-related confinement, only essential workers (such as fire fighters and medical workers) were allowed to commute. At such times, air traffic fell by 75 percent, the team reports. Car and truck traffic at that time fell by about 50 percent. Electric power use shrank far less, only by about 15 percent.
Such drops in CO2 pollution will be hard to keep up
What will happen if and when the world returns to a pre-pandemic level of activity? If it happens by mid-June, the researchers say, 2020’s CO2 emissions will be about 4 percent lower than last year’s. If much travel is restricted through the end of the year, CO2 emissions for the year could be as much as 7 percent lower than in 2019.
Such a steep decline in CO2 will be hard to keep up, says coauthor Rob Jackson. He’s an environmental scientist at Stanford University in Palo Alto, Calif. The drop came at a very high cost. It brought a major change in how — and how many — people worked and played. However, the changes also offer a lesson for people interested in slowing the growth of climate impacts.
Sharp cuts in the use of fossil fuels will be needed to reach emissions targets set in 2015 by the United Nations’ Paris Agreement. For instance, that treaty calls for trying to limit global warming to below 2 degrees Celsius (3.6 degrees Fahrenheit) by 2100. Even better would be limiting warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit). To do that, nations would need to reduce emissions by 7.6 percent each year for the next 10 years, scientists say. That’s more, each year, than the reductions that would likely occur this year if pandemic-related travel limits persisted through December 31.