The U.S. Environmental Protection Agency (EPA) will soon follow up on previously-discussed plans to set emissions standards for airplanes.
The agency previously identified airplane emissions as a threat to human health because of their contribution to climate change, but has not been able to issue actual rules governing those emissions.
Now the Obama Administration is pushing the EPA to draft those rules in what will likely be one of its last actions on climate change.
Draft airplane-emissions rules could be completed by January, according to The New York Times.
That would leave responsibility for finalizing and enacting the new standards to the next presidential administration.
Airlines account for just 2 percent of global carbon emissions, but many analysts believe their emissions could triple by the middle of the century if projected growth in air travel occurs.
KLM biofuel-powered airliner (KLM)
Still, regulating aircraft emissions presents some challenging legal issues.
The previously-issued legal finding—called an "endangerment finding"—that marked airplane emissions as a contributor to climate change gives the EPA authority to regulate them under the Clean Air Act.
But due to the global nature of the airline industry, the administration has held off on attempting to issue emissions standards until now.
Airlines are already grumbling at the prospect of tighter standards, with industry lobbying group Airlines for America claiming they could endanger passenger safety by forcing airlines to adopt unproven technology.
Instead, the airline industry has advocated rules that echo standards published earlier this year by the International Civil Aviation Organization (ICAO)—the United Nations' aviation agency.
If enacted, those standards would require a 4-percent reduction in carbon-dioxide emissions from 2015 levels for new aircraft beginning in 2028.
Boeing 787 Dreamliner
They would also set new limits for airplanes already in production that would be delivered after 2023, with emissions reductions of 0 to 11 percent, depending on a plane's size.
But environmental groups have criticized this set of rules, claiming it won't effectively restrain airline-emission growth—and noting that they also don't address aircraft already in service.
The Center for Biological Diversity has pressed the EPA to draft tougher standards than those from the ICAO, believing strong U.S. rules could serve as a model for other countries.
Even if the U.S. adopts the ICAO standards, it would still have leeway to create stricter standards of its own.