Peter Liese, a member of the European Parliament from the conservative German Christian-Democratic Union, led a delegation to meet with Obama administration officials in Washington last week to discuss the issue.
The International Civil Aviation Organization (ICAO), the United Nations' civil aviation body, has until September to complete a resolution on a market-based plan that would curb rising greenhouse gas emissions from global airlines.
Should the UN organisation fail, the EU could try to re-impose an emissions trading system on global airlines. The EU postponed the implementation of the law in 2012 to give the ICAO time to devise a global approach.
Liese sees only a 50% chance the ICAO talks can deliver a deal strong enough to avoid a revival of the law and avoid threats of a trade war.
"Unless we have progress in the next six to seven weeks, we will run into a big problem," Liese told Reuters.
Liese said drafts of the resolution that ICAO assembly delegates will consider at their triennial meeting, which starts in Montréal on 24 September, might not be not ambitious enough to pass muster.
"We made very clear that what is on the table now is not enough," Liese said.
He added that a deal acceptable to Europeans would unambiguously clarify that there will be an international agreement from 2020 onward.
The ICAO narrowed its options in May to three market-based measures, including a mandatory offsetting scheme.
The following month, the International Air Transport Association (IATA), set up to help the UN harmonise aviation after the second world war, backed a system in which airlines would offset increased emissions after 2020 by buying carbon credits from projects that cut them in other sectors. A wider coalition of aviation groups endorsed the plan in recent weeks.
Nancy Young, vice president for environmental affairs for US airline lobby group Airlines for America, said the strong industry backing of a market-based emissions plan should give the ICAO "very strong momentum to reach an agreement."
The agreement, she said, will not be a detailed framework, but "a glide path toward a single market-based measure by 2016," the year the next ICAO assembly takes place.
The ICAO's 36-member leadership council is scheduled to meet on 4 September.
Meetings between countries with similar views on the issue also have been taking place. For example, China and India, which along with the United States strongly opposed the imposition of the European trading scheme on their airlines, are likely meeting ahead of the assembly to coordinate objections to the ICAO's proposed resolution.
Liese said US and EU officials might also have to consider a potential bilateral agreement if the ICAO fails to agree on a deal that would stave off the threat of a trade war.
But Jos Delbeke, director-general for climate action for the European Commission, was optimistic and said he was confident a useful resolution is going to be adopted in September or October.