For two years, President Barack Obama has used his executive power to impose new rules to cut carbon emissions, targeting cars and power plants, buoying environmentalists and infuriating industry.
His latest foray - regulating commercial aviation - had the opposite effect.
On Wednesday, the administration took a first step toward cutting greenhouse gas emissions from the nation's fleet of aircraft, releasing a scientific finding that said emissions from plane engines pose a risk to human health because they contribute to climate change.
But the Environmental Protection Agency (EPA) did not immediately propose new regulations. Instead, it signaled it would implement a global emissions standard being developed by the United Nations' International Civil Aviation Organization (ICAO) that is due to be released next year.
Those rules are expected to apply only to new aircraft designs beginning in 2020, leaving most of the world's existing fleets unaffected for years to come.
That decision was greeted with cautious optimism from the aviation industry, which says it is making strides on energy efficiency and wants the United States to coordinate any new regulations with the rest of the world.
That was precisely what worried environmentalists, who warned that relying on a global agreement forged under UN auspices seeking consensus would be doomed to produce weak rules.
"The EPA is declaring aircraft greenhouse gases to be dangerous to all of us, but is passing the buck on doing anything about it," said Vera Pardee, an attorney for the Center for Biological Diversity that was among several green groups pushing the administration for years to adopt new regulations.
Indeed, the EPA was prodded to act on aviation only after a long legal fight. A collection of environmental groups petitioned the agency to bring in new aviation regulations in 2007 and sued it to do so in 2010, winning a federal court ruling two years later that ordered the U.S. government to regulate aircraft emissions under the Clean Air Act.
On Wednesday, the EPA acknowledged "certain classes of airplane engines contribute to air pollution that causes climate change endangering public health and welfare," and promised to follow ICAO's lead on new rules.
Airline companies were broadly supportive of the administration's approach. The industry favors a global standard over national standards because carriers operate all over the world and want to avoid a patchwork of rules and measures, from taxes to emissions trading programs.
"We feel this is the right thing for the EPA to be doing, as a precursor to be able to adopt what comes out of ICAO," said Paul Steele, senior vice president at the International Air Transport Association.
"If you're a big airline and you're flying to 100 countries a day, then complying with all those different regimes is an administrative nightmare."
Controlling aviation emissions is seen by climate scientists as a vital cog in the wider attempt to curb global warming. Commercial aviation accounted for three per cent of overall U.S. emissions and 11 percent from the U.S. transportation sector in 2013, the EPA said. The U.S. industry was responsible for nearly 30 percent of global aircraft emissions in 2010, the latest year with complete global emissions data.
Environmental groups cite studies indicating unregulated aviation emissions could triple by 2050, and they have been critical of the ICAO negotiations, saying the organization's targets are not ambitious.
Sarah Burt, an attorney with Earthjustice, another organization that sued the EPA, said ICAO is poised to set a "business-as-usual" standard that will lock in emissions increases for decades to come.
"The ICAO standard won't deliver substantial reductions because they are setting a standard that 90–95 percent of aircraft already meet," she said, adding that planes tend to stay in service for 20 to 30 years.
The burden for meeting those lower emissions standards will fall to aircraft and engine manufacturers such as Boeing Co, Airbus Group SE, Pratt & Whitney and Rolls Royce [RROYC.UL]
But some experts want the new standards to apply to any plane delivered to carriers after 2020, rather than simply for newly designed aircraft.
"Applying the standard to all new aircraft delivered after 2020 is key," said Dan Rutherford, director of the International Council on Clean Transportation Program. "If ICAO grandfathers in existing designs, the standard would cover only about 5 percent of the global fleet by 2030."
An EPA spokesman defended the decision to work through ICAO, arguing that an international standard would cover more planes than a simple domestic one.
But some critics want the White House to seek more aggressive targets than what is achievable under the consensus-driven international organization.
“If the Obama administration wants this to stand up next to its much more ambitious cars and power plants rule, it will need to do much more than follow the weak lead of ICAO,” said Burt of Earthjustice.