Airlines on Tuesday called on governments to voluntarily sign up to a global deal designed to reduce carbon dioxide emissions from aviation, saying they would have preferred a "more ambitious" timeline.
The proposed new deal on aviation, which aims to cap the carbon pollution of all international flights at 2020 levels, will be voluntary between 2021 and 2026 and then mandatory from 2027 for the world's largest emitters.
Airlines in participating countries would need to limit their emissions or offset them by buying carbon credits from designated environmental projects around the world.
China, the United States and Europe all pledged support on Saturday for the deal, which is due to be finalised at a meeting of the United Nations' International Civil Aviation Organisation (ICAO) in September.
The International Air Transport Association (IATA), which represents more than 260 airlines accounting for about 83 per cent of global air traffic, highlighted how the scheme was initially intended to be mandatory from the start.
"The industry is ready. There is really no reason for governments not to volunteer," IATA Director General Alexandre de Juniac said in a statement on Tuesday.
He said he was optimistic that an agreement would be reached at the ICAO meeting.
"What is most important is that the substance of the negotiating text will allow for meaningful management of aviation's carbon footprint," he said.
Airlines have said they want one global deal to reduce carbon dioxide emissions from air travel despite the higher costs they would incur in order to avoid a patchwork of regulation that would be harder to manage.
On Monday the director of the Air Transport Action Group, another industry organisation, also urged countries to be more ambitious on the ICAO deal.
"We do not feel a pilot phase is necessary because airlines and other aircraft operators will be ready and able to commence the scheme from 2020," executive director Michael Gill said in a statement, saying that many airlines already offered offsetting to passengers on a voluntary basis