First it happened in China. Now, Italy.

The coronavirus struck hard, and authorities responded with sweeping interventions to keep people from spreading the disease further. As citizens hunkered down at home, businesses and roads suddenly fell empty and silent. One startling result: a decline in air pollution and greenhouse gas emissions.

The Washington Post this week analyzed data from the European Space Agency’s Sentinel-5P satellite, which can measure concentrations of greenhouse gases and other pollutants in the lower atmosphere. It shows that between Jan. 1 and March 12, concentrations of nitrogen dioxide, or NO2, fell drastically, especially over hard-hit northern Italy.

Nitrogen dioxide is not one of the major greenhouse gases linked to climate change. But it is produced from combustion – by cars, power plants, and other industrial sources. So it serves as a proxy for other emissions that warm the atmosphere. It also is a pollutant that can increase the risk of asthma, inflammation of the lungs and other harmful health conditions. Several experts told The Washington Post that the changing concentrations probably reflect the decline of driving in particular, in a country in which more than half of cars burn diesel.

“I guess this is mostly diesel cars out of the road,” Emanuele Massetti, an expert on the economics of climate change at Georgia Tech University who has studied Italy’s climate policies, said in an email.

“I expect pollution to drop even further as the particles in the atmosphere (concentration) get either dispersed or absorbed,” he continued. “In a few days, they will enjoy the cleanest air ever in northern Italy.”

That shift is little comfort, of course, to a region in the grips of a deadly outbreak, wrestling with an overwhelmed health system and understandably focused on the crisis at hand rather than the long-term effects of climate change. At the same time, the stark changes offer yet another example of the impact humans have on the environment – and how swiftly emissions can vanish when humans drastically reduce the burning of fossil fuels.

Despite the wide use of diesel engines, Italy’s electricity sector doesn’t burn a massive amount of coal, Massetti said – rather, it is driven largely by natural gas and renewable energy.

Greenhouse gas emissions in the country also have plummeted in recent years. That’s one reason Massetti said he thinks the emissions decline mainly represents a steep decrease in the driving of diesel vehicles. The transportation sector produces more than 70 percent of all nitrogen dioxide emissions in Milan, according to a recent analysis by the European Commission’s Joint Research Center.

“This makes a lot of sense especially since it shows that the highest decrease in concentration has happened in Lombardy, where the most stringent choices were taken first,” Edoardo Marcucci, who directs the Transport Research Lab at Roma Tre University in Rome, said in an email. “I would expect that to become true for the whole country in the next few days.”

Riccardo Valentini, a professor at Italy’s University of Tuscia and director of the impacts division of the Euro-Mediterranean Center on Climate Change, said in an email that the country’s aggressive measures to contain the virus have had a profound effect on everyday life – and by extension, on emissions.

“Nobody can go out from homes unless for precise working duties and/or food purchase or health emergency,” he said. “For sure, there has been a decline of car traffic everywhere. This explains the NOx emission decline.”

He added that Italy’s troubles could potentially soon extend throughout the region and to other parts of the globe. “We are the first E.U. country to get the epidemic outbreak, but numbers are increasing in Spain, France and Germany, plus the others,” Valentini wrote, adding, “The real impact on climate policies could vary country by country depending on the size of the containment measures.”

In the United States, for example, school closures, event cancellations and work-from-home policies will mean millions of people are no longer commuting by car during rush hour, resulting in pollution declines here, too. Beyond the public health and economic crises, he said, the pandemic ultimately could trigger the most significant reduction of greenhouse gas emissions of the past century.

While the ongoing crisis has drastically slowed emissions in China, Italy and potentially elsewhere, that has offered little cause for celebration.

“It is, of course, not a good thing,” Valentini wrote. “This is not the way to reduce emissions!”

Climate advocates agree, saying the current catastrophe is not the way any reasonable person would envision the world lowering its carbon footprint. In addition, the outbreak has halted meetings to plan for public protests for climate action in the coming months, as well as the global push to get nations to commit to more ambitious emission reduction plans at a key U.N. summit scheduled for this fall.

Moreover, the drop in emissions is expected to be temporary. “This will have just a minor effect of global concentrations of CO2, unless it leads to a really long depression of the world economy,” Massetti said.

Italy has been a world leader in its reductions of greenhouse gases in recent years. Carbon dioxide emissions in the country declined by over 30 percent between 2004 and 2018. Last year, Italy announced that it planned to become the first country to make it mandatory for schoolchildren to learn about climate change and sustainable development.

Italian education minister Lorenzo Fioramonti said at the time that beginning this September, teachers in all state schools and all grades would dedicate 33 hours per year – nearly an hour per week of instruction – to issues related to climate change and environmental sustainability.

For now, however, all schools in Italy remain closed.