U.S. greenhouse-gas emissions fell 2.1 percent last year almost entirely because of a sharp drop in coal consumption, according to the Rhodium Group, a private data-research firm.

Coal-fired electric power generation, which had rebounded slightly in 2018, fell by a record 18 percent to the lowest level since 1975, the Rhodium study said. Coal burning produces carbon dioxide, which fuels climate change.

But much of that reduction was offset by rising emissions from the use of inexpensive natural gas. And transportation emissions remained relatively flat while emissions from buildings, industry and other parts of the economy grew.

The modest overall drop in emissions left the United States in danger of failing to meet its commitments under international agreements.

“Last year was definitely a good news, bad news story,” said Trevor Houser, a partner with the Rhodium Group and head of its energy and climate team. “There was the biggest drop ever in electric power emissions but little progress in other sectors of the economy.”

Moreover, Houser said, “emissions are not falling fast enough to meet Copenhagen or Paris agreement targets without a significant change in public policy.”

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In 2019, U.S. greenhouse gas emissions were roughly 12 percent below 2005 levels. That puts the United States at risk of missing the 17 percent target it agreed to reach by 2020 under the 2009 Copenhagen Accord, the Rhodium study said. In addition, U.S. emissions last year were still “a long way off” from the 26 percent to 28 percent reduction that the United States pledged to carry out by 2025 under the 2015 Paris climate agreement, the study said. The Trump administration has said it will withdraw from the Paris accord next fall.

The United States accounts for 11 percent of global greenhouse-gas emissions, Houser said.

The Rhodium study comes after U.S. emissions in 2018 rose by 2.7 percent, so net U.S. greenhouse-gas emissions ended 2019 slightly higher than at the end of 2016.

And even though the rate of emissions changed directions, the study said, “unfortunately there was little good news outside the power sector.”

Emissions from cars, trucks, planes and other vehicles declined slightly — by 0.3 percent. But industrial emissions rose 0.6 percent; direct emissions from buildings increased by 2.2 percent; and emissions from other sectors — including agriculture, waste, land use, oil and gas methane — jumped 4.4 percent.

To meet goals for lower levels of climate pollution in the future, the United States would have to make broad, sharp reductions in part because further cuts in coal use, which fell by half over the past decade, will be more difficult.

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“Hitting the Copenhagen Accord’s 17 percent target exactly will require a 5.3 percent reduction in net GHG emissions this year — a bigger annual drop than the US has experienced during the postwar period, with the exception of 2009 due to the Great Recession,” the study said.

Meeting the Paris agreement targets will require reductions three times as fast over the next six years as over the past 14 years.

“It’s still possible, but will require a significant change in federal policy — and pretty soon,” the report said.

One factor that lowered the emissions level was the slowdown in the economy overall. Growth slowed to 2.3 percent in the first three quarters of 2019, down from a 2.9 percent pace in 2018.

The change was seen most clearly in the slowdown in freight moved by truck, from 7.1 percent year-on-year during the first three quarters of 2018 to 4.1 percent during the same period in 2019, the study said. “That turned a 5.6 percent increase in year-on-year diesel demand during the first three quarters in 2018 to a 0.8 percent decline during the same period in 2019,” it added.

The greenhouse-gas figures are preliminary, but the Rhodium Group has correctly pegged the direction and general magnitude of emissions changes. A year ago, its preliminary estimate said U.S. emissions climbed 3.4 percent, and the final increase was 2.7 percent. For 2017, its preliminary estimate said there was a 1 percent decrease, and the final number was a 0.8 percent decline.

Global emissions of carbon dioxide from fossil fuels and industry were expected to grow slowly in 2019 because of a drop in global coal use, according to a Global Carbon Project study released Dec. 4 at the international climate conference in Madrid. The Global Carbon Project is an academic consortium that produces the figures annually.

The growth rate in 2019 was expected to slow to 0.6 percent, down from 2.1 percent the previous year. The more modest growth was caused by declines in coal use in the European Union and the United States, as well as slower growth in coal use in China and India, the group said.