China and Europe are failing to agree on greenhouse gas emission caps from the aviation sector, a senior EU official has said.
Any airlines landing in Europe must comply with the controversial cap scheme from January next year and cover any surplus emissions with carbon credits.
China has criticised the policy as illegal and unfair and urged the EU to exempt its airlines from the scheme, as well as threatening to retaliate by reducing its aircraft orders from Europe's Airbus.
Jos Delbeke, the director general for climate action at the European Commission, told a news briefing that he had a "very useful exchange of views" with his Chinese counterparts on the issue during his visit to Beijing.
Europe was entitled to impose the law after other countries failed to agree to curb aircraft emissions, he said.
"Multilateral agreements are preferable but our legislators got impatient because the multilateral agreements did not get any results," Delbeke said.
"This is a measure the EU is entitled to take according to international law."
He said the law was an "old story" that was first passed in 2009 and adopted following years of discussions with airlines, industry associations and other countries, and that opponents in the United States, China and elsewhere had only started to pay attention to the issue this year.
"It is only just a couple of months before the starting date that this law seems to provoke quite a bit of anxiety," he said.
Delbeke added the impact of the law was likely to be minimal, with 85 per cent of emission permits granted free in the first year of implementation, giving airlines the opportunity to earn revenues that would allow them to modernise their fleets.
He said he was confident that a challenge to the law made by two U.S. airlines would be rejected, particularly after the EU's advocate general ruled that it did not violate either the Chicago Convention on Civil Aviation or the United Nations Framework Convention on Climate Change.
Delbeke said that the law would encourage countries to implement their own aviation CO2 emission cap.
"It opens up the possibility that if a state takes equivalent measures we can waive the obligations."
Europe has been trying to persuade China, the world's biggest source of climate-changing greenhouse gases, to make stronger commitments to reduce its emissions.
China has sought to retain the Kyoto Protocol principle of "common but differentiated responsibilities" in which the bulk of the burden for reducing CO2 lies with industrialised nations.
Delbeke said the principle applies only to nations, and not to individual industrial sectors, and that discussions on the law would continue.
"We are going to continue our negotiations and discussions and different parties -- that's what we agreed today with China," he said.
"In case we do not find a solution at the political level, then airlines may want to go to court and challenge the measure. We have the rule of law in Europe and anybody who is dissatisfied can go to court."