Washington: Jet engine exhaust from airliners endangers human health and adds to climate change, the government found today in taking the first step toward regulating those emissions.

The Environmental Protection Agency said it will use its authority under the Clean Air Act to impose limits on aircraft emissions.

Jet engines spew significant amounts of greenhouse gases, including carbon dioxide and methane, into the upper atmosphere, where they trap heat from the sun. But proposed rules such as imposing fuel-efficiency standards have faced stiff opposition from aircraft makers and commercial airlines.

Aircraft emissions were not addressed as part of the landmark global climate agreement agreed to in Paris in December. Addressing pollution from aircraft is an important element of US efforts to address climate change, said Janet McCabe, EPA’s acting assistant administrator for air and radiation.

McCabe said aircraft are the third largest contributor to greenhouse gas emissions in the US transportation sector, and that is expected to increase. Cars and trucks already are regulated. The EPA’s findings do not apply to small piston-engine planes or to military aircraft.

A UN panel in February recommended new emissions standards for international flights that require an average 4 percent reduction in fuel consumption during the cruising phase of flight. The new regulations from the International Civil Aviation Organization require that new aircraft designs meet the standards beginning in 2020, and that designs already in production comply by 2023.

Environmental groups have criticized those new international standards as too weak to actually slow global warming. Planes burn the most fuel during takeoffs and landings. Cruising at high altitudes is the most fuel-efficient period. Environmentalists say aviation accounts for about 5 percent of global greenhouse emissions, though the UN and EPA cite studies concluding it’s actually less than 2 per cent.

The EPA finding announced today is expected to result in fuel-efficiency standards for domestic carriers, which critics call long overdue. The EPA acted after a coalition of environmental organizations filed notice of their intent to sue the agency over its inaction.