The major shock to economic activity wrought by the COVID-19 pandemic led to a 10.3% drop in U.S. greenhouse gas emissions in 2020, the largest single drop in emissions since the World War II era, a new analysis of preliminary economic and energy data from consultancy firm Rhodium Group found.

Rhodium Group wrote that because of the reduced economic output, the United States is expected to see 2020 emissions 21.5% below 2005 levels, far exceeding its 2020 Copenhagen Accord target of a 17% reduction below 2005 levels. That puts the country's emissions below 1990 levels for the first time in three decades.

"However, 2020 should not in any way be considered a down payment toward the U.S. meeting its 2025 Paris Agreement target of 26% to 28% below 2005 levels," the Jan. 12 report notes. "The emission reductions of 2020 have come with an enormous toll of significant economic damage and human suffering."

Rhodium Group noted the last substantial drop in the U.S. came when greenhouse gas emissions fell 6.3% during the Great Recession of 2009.

In 2020, some of the sectors hardest hit by the economic impact of the virus, such as transportation, electric power and industry, are also leading sources of greenhouse gas emissions. According to the analysis, the greatest decline came from the transportation sector, where greenhouse gas emissions fell 14.7% between 2019 and 2020.

Emissions from the electric power sector, which has been experiencing declining emissions from the steady retirement of coal-fired power plants, slid 10.3% below 2019 levels in 2020. Emissions from coal-fired power plants were down nearly 19% year on year.

"That's the largest year-on-year decline in recorded history, breaking last year's record fall," the report states.

Rhodium noted that the impact on the industrial sector was "mixed" based on the sub-sector and time of year. Over the year, emissions declined about 7% from 2019 levels.

"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," the report concludes. "With growth expected to bounce back in 2021 (most forecasts currently project GDP growth of 3 to 4%), emissions will likely increase as well absent a concerted effort."