WASHINGTON— Environmental groups threatened today to sue the Trump administration for failing to fulfill its obligation under the Clean Air Act to curb planet-warming pollution from airplanes.

The Center for Biological Diversity and Friends of the Earth, represented by Earthjustice, sent a legal notice to the Environmental Protection Agency highlighting that pollution from aircraft is rising steeply and that the EPA is skirting its duty to implement a reduction plan. Planes are already the third-largest source of transportation-related greenhouse emissions, and the industry is expected to generate 43 metric gigatons of CO2 through 2050.

In 2016 the EPA determined that aircraft pollution drives climate change and endangers public health and welfare. That determination requires officials to set aviation emission limits, but three years later the Trump administration has yet to act.

“The Trump administration’s refusal to curb plane pollution is fueling the climate crisis,” said Clare Lakewood, climate legal director at the Center. “Airplane pollution is increasing at really worrying rates, but the EPA just keeps refusing to address this skyrocketing threat to our rapidly warming planet. We’re taking action to make sure the agency complies with its legal obligations, because there’s just no time left for foot-dragging.”

“The Clean Air Act requires that the Trump administration take action on greenhouse gases from aircraft,” said Hallie Templeton, interim legal director at Friends of the Earth. “It’s catastrophic that the administration has deferred their plan for over a decade on such a pressing matter. The court must put the law above the politics of climate change-denial by requiring the agency to curb dirty greenhouse gas emissions from aviation.”

Flights departing from airports in the United States and its territories are responsible for almost one-quarter of global passenger-transport-related carbon emissions. Yet former EPA Administrator Scott Pruitt failed to release a planned carbon-emissions reduction requirement for jet engines in new plane models. In 2019 the EPA announced it would release a proposed rule on aircraft greenhouse emissions by September, but it failed to do so.

In 2010 the Center, Friends of the Earth and other organizations represented by Earthjustice sued the EPA to force it to set greenhouse pollution standards for airplanes. A judge ruled that the agency is required to address aviation emissions under the Clean Air Act.

“This letter puts EPA on notice that their job isn’t done when it comes to pollution from aircraft,” said Sarah Burt, staff attorney at Earthjustice. “Four years after concluding that aircraft are endangering Americans’ health and contributing to the climate crisis, it is past time for common-sense steps to reduce this source of pollution.”