The wave of lockdowns and shuttered economies caused by the coronavirus pandemic fueled a momentous decline in global greenhouse gas emissions, one unlikely to last, a group of scientists reported Tuesday.
As coronavirus infections surged in March and April, nations around the globe experienced an abrupt reduction in driving, flying and industrial output, leading to a startling decline of more than a billion tons of carbon dioxide emissions. That includes a peak decline in daily emissions of 17% in early April, according to the study published in the journal Nature Climate Change. For some nations, the drop was much steeper.
Scientists have long insisted that the world must drastically scale back carbon pollution - and quickly - to mitigate the worst effects of climate change over coming decades, though none have suggested that a deadly global pandemic is the way to accomplish it.
The study released Tuesday projects that total emissions for 2020 probably will fall between 4% and 7% compared with the prior year - an unheard-of drop in normal times, but considerably less dramatic than the decline during the first few months of the year, when economies screeched to a halt. The final 2020 figure will depend on how rapidly, or cautiously, people around the world resume ordinary life.
The unprecedented situation produced by the virus has offered a glimpse into the massive scale required to cut global emissions, year after year, in order to meet the most ambitious goals set by world leaders when they forged the 2015 Paris climate accord. Last fall, a United Nations report estimated that global greenhouse gas emissions must begin falling by 7.6% each year beginning in 2020 to avoid the worst effects of climate change.
Tuesday's study underscores how far the world remains from that long-term aspiration. The forced plunge in greenhouse gas emissions in recent months, while extraordinary, returned carbon pollution levels to those last seen in 2006. And the recent changes probably will not last.
"History suggests this will be a blip," said Rob Jackson, a Stanford University professor and one of the authors of the peer-reviewed study, which attempts to assess the virus's impact by nation and economic sector. "The 2008 [financial] crisis decreased global emissions 1.5% for one year, and they shot back up 5% in 2010. It was like it never happened."
While the decline in emissions during the pandemic may have been unprecedented, it was relatively small when it comes to combating global warming. The peak 17% decline in global emissions - which occurred in early April - meant nations continued to generate more than 80% of carbon pollution.
Researchers say the experience demonstrates how broad structural changes to the energy system are critical if the world is to slash emissions in a meaningful, sustainable way.
"We can see now that behavior change alone is not going to do it," said Corinne Le Quéré, lead author of the study and director of Britain's Tyndall Center for Climate Change Research.
Le Quéré said she expected to find larger reductions in the power and industrial sectors during the pandemic. Instead, she said, many sources of carbon dioxide and other pollutants have continued steadily, almost on autopilot, even as much of the world has ground to a halt.
Appliances continue to run, office buildings must be maintained, and some factories continue to hum.
"There's a lot of inertia in the infrastructure, in the built environment," she said. "It seems like many things are able to function on their own, at least for a short time."
Emissions have fallen before - during world wars and economic recessions, for instance, and markedly during the Great Depression. But experts do not think the modern world has seen a plunge so sudden and sharp as in recent months.
"In absolute terms, it will be the biggest," said Glen Peters, one of the study's authors and an expert at the Center for International Climate Research in Norway. "In relative terms, you will have to go back quite some [time] to find big changes like that."
Most researchers agree that emissions are all but certain to bounce back once countries reopen. Already, demand for energy is resuming as people return to the roads and many U.S. states begin easing stay-home orders that helped drive the price per gallon of gasoline to less than $1 at some pumps.
Governments also are expected to begin trying to boost their economies with stimulus spending in the coming months. But how leaders decide to spend that money could make a fundamental difference.
"Where they put this stimulus is really critical," Le Quéré said. "It's 2020, and there's not much time to tackle climate change."
Some world leaders have pledged to push for a shift toward greener economies in the wake of the pandemic.
Last week, British Prime Minister Boris Johnson said his country's push to slash its emissions remains "undiminished" by the coronavirus and the economic turmoil it has caused. He singled out airlines during remarks in Parliament last week, saying the sector must limit its carbon emissions even when normal flights resume.
"Inadvertently, the planet this year will [have] greatly reduced its CO2 emissions. . . . We need to entrench those gains," Johnson told lawmakers. "I don't want to see us going back to an era of the same type of emissions as we've had in the past. Aviation like every other sector must keep its carbon lower."
Last month, German Chancellor Angela Merkel also indicated that she would support green investments as her nation seeks to restore its economy.
"It will be all the more important that if we set up economic stimulus programs, we must always keep a close eye on climate protection," Merkel told a gathering of leaders focused on climate change.
The new research was conducted by Le Quéré, Jackson, Peters, and 10 other colleagues affiliated with the Global Carbon Project.
Normally, global emissions are calculated on an annual basis; doing so more rapidly, nearly in real time, presented a scientific challenge. Tuesday's study used a combination of energy data across multiple sectors, as well as data on the strenuousness of lockdowns across 69 countries that account for 97% of the world's greenhouse gas emissions to estimate the reductions.
The results varied greatly across sectors. Airplane emissions plunged by as much as 60% - but airlines represent a relatively small fraction of global emissions. Emissions from surface transportation, one of the largest sources, fell 36% at the peak of the lockdowns.
"Passenger vehicles are down a bit more," Jackson said. "Commercial vehicles and long-haul trucking are down much less. I'm staying at home, but the Amazon delivery vehicle is still driving around."
Emissions tied to home energy use increased about 3%, not surprising during a time when people are confined to their homes, using more appliances, lighting, heating and cooling. But industrial electricity demand plummeted, leading to net electricity declines overall.
While some aspects of life might change in the wake of the pandemic - more people working remotely, fewer people commuting and taking frequent plane trips - individual changes probably will not make much of a long-term mark on emissions, said Zeke Hausfather, a scientist and director of climate and energy at the Breakthrough Institute.
"Unless anything structurally changes, we can expect emissions to go back to where they were before this whole thing happened," Hausfather said.
He also said one year of sharp reductions in emissions will do little to stave off the warming that scientists have said will continue unless the world drastically cuts emissions for good.