Emissions plunged more than 10 percent. If the trend can be sustained, it would put the United States within striking distance of one of its major goals under the Paris climate agreement.

 
 
Credit…Jim Lo Scalzo/EPA, via Shutterstock

WASHINGTON — America’s greenhouse gas emissions from energy and industry plummeted more than 10 percent in 2020, reaching their lowest levels in at least three decades as the coronavirus pandemic slammed the brakes on the nation’s economy, according to an estimate published Tuesday by the Rhodium Group.

The steep drop, however, was the result of extraordinary circumstances and experts warned that the country still faced enormous challenges in getting its planet-warming pollution under control. In the years ahead, United States emissions are widely expected to bounce back once the pandemic recedes and the economy rumbles back to life — unless policymakers take stronger action to clean up the country’s power plants, factories, cars and trucks.

“The most significant reductions last year were around transportation, which remains heavily dependent on fossil fuels,” said Kate Larsen, a director at Rhodium Group, a research and consulting firm. “But as vaccines become more prevalent, and depending on how quickly people feel comfortable enough to drive and fly again, we’d expect emissions to rebound unless there are major policy changes put in place.”

Before the pandemic hit, America’s emissions had been slowly but steadily declining since 2005, in large part because utilities that generate electricity have been shifting away from coal, the dirtiest fossil fuel, in favor of cheaper and cleaner natural gas, wind and solar power. Over the past decade, utilities have retired hundreds of coal-burning power plants despite President Trump’s efforts to revive the industry.

 

Then, the coronavirus arrived. As governors placed their states under lockdown last spring and Americans sheltered in place, emissions started plunging across parts of the economy that had rarely seen sustained drops before.

Transportation, the nation’s largest source of greenhouse gases, saw a 14.7 percent decline in emissions in 2020 as millions of people stopped driving to work and airlines canceled flights. While travel started picking up again in the latter half of the year as states relaxed their lockdowns, Americans drove 15 percent fewer miles over all last year than they did in 2019 and the demand for jet fuel fell by more than one-third.

 
 
Credit…Lucy Nicholson/Reuters

Emissions from heavy industry, such as steel and cement, dropped 7 percent in 2020 as automakers and other manufacturers churned out fewer goods amid the economic slump. America’s buildings, which produce carbon dioxide when they burn oil or natural gas for heat, saw emissions fall 6.2 percent, driven by both lockdowns and warmer-than-average weather.

In the electricity sector, emissions plunged by 10.3 percent in 2020, driven by a sharp decline in coal burning. As electricity demand sagged nationwide, utilities ran their coal plants far less often because coal has become the most expensive fuel in many parts of the country. Instead, they used more natural gas — which produces less carbon dioxide than coal, but still generates significant heat-trapping methane — and drew more heavily on emissions-free wind and solar power.

 

Renewable energy surged in 2020, as energy companies overcame disruptions from the pandemic to build a record number of new wind turbines and solar panels ahead of a key deadline to claim a federal tax credit. The United States produced roughly as much electricity from renewable sources last year as it did from coal, a milestone that has never been reached before.

 
 
Credit…European Space Agency, via Agence France-Presse — Getty Images

Over all, the fall in emissions nationwide was the largest one-year decline since at least World War II, the Rhodium Group said, and put the United States within striking distance of one of its major climate goals under the Paris agreement, a global pact by nearly 200 governments to address climate change.

As part of that agreement, former President Barack Obama had pledged that United States emissions would fall 17 percent below 2005 levels by 2020. President Trump disavowed the Paris pact, and, before last year, it looked like the United States would miss that target. But in the wake of the pandemic, America’s industrial emissions are now roughly 21.5 percent below 2005 levels.

But that milestone comes with several caveats. First, those numbers don’t account for any uptick in emissions resulting from last year’s record-setting wildfires in the West, which burned millions of acres of forests and grasslands, sending the carbon dioxide locked away in all those trees into the atmosphere.

 

One preliminary estimate in November from BloombergNEF suggested that wildfires could offset roughly 3 percent of last year’s drop in American emissions from energy and industry. While many trees that went up in flames will eventually grow back, absorbing carbon dioxide as they do, that process will take years. And scientists have warned that wildfires will become larger and more frequent as the planet warms.

 

The other caveat is that America’s emissions could tick back up again once vaccines are widely distributed and the economy recovers. The Rhodium Group report noted that a similar rebound occurred after the financial crisis of 2008-9 caused emissions to fall sharply. And it noted that many sectors, like air travel and steel making, have already been rebounding in recent months.

“Unfortunately, 2020 tells us little about what we can expect to see in 2021 and beyond,” the report concluded. “The vast majority of 2020’s emission reductions were due to decreased economic activity and not from any structural changes that would deliver lasting reductions in the carbon intensity of our economy.”

 
 
Credit…Brian Snyder/Reuters

Scientists warn that even a big one-year drop in emissions is not enough to stop global warming. Until humanity’s emissions are essentially zeroed out and nations are no longer adding greenhouse gases to the atmosphere, the planet will continue to heat up. As if to underscore that warning, European researchers announced last week that 2020 was quite likely tied with 2016 as the hottest year on record.

President-elect Joseph R. Biden Jr. has called global warming a top priority, setting a goal of slashing America’s emissions to net zero by 2050. Doing so, experts said, would require major new steps to accelerate the use of renewable electricity, shift Americans from gasoline-burning cars to cleaner electric models and rethink methods for processes like home heating or steel and cement production.

And those efforts would need to be replicated across the globe. On Monday, the International Energy Agency said it would publish a detailed blueprint in May for how the global economy could reach net-zero emissions by 2050, noting that the worldwide drop in greenhouse gas emissions last year was likely to prove temporary unless nations took the opportunity to rethink their reliance on fossil fuels.

“Nothing short of a total transformation of our energy infrastructure will be required,” said Fatih Birol, the agency’s executive director. “That calls for decisive action this year, next year and indeed every year to 2050.”

New York Times Climate News