The world has finally agreed on a long-term plan to curb carbon emissions from flying.

At a meeting in Montreal, the International Civil Aviation Organisation (ICAO), pledged to support an "aspirational" net zero aviation goal by 2050.

The plan, seen as a compromise by many, was accepted by the 193 countries who are members of ICAO.

However green groups say the deal is weak and not legally binding.

When the world came together in Paris in 2015 to agree on a long-term plan to tackle climate change, two key industries were missing - aviation and shipping.

The airline industry contributes around 2.5% of global carbon emissions, but scientists believe it has a much higher impact on climate change than this figure suggests.

This is because of the multiple impacts of flying including the altitudes planes fly at and the effects of contrails - the water-vapour trails produced by engines.

US Special Presidential envoy on climate change, John Kerry, welcomed the deal.

In a tweet he said: "Thrilled to see international aviation commit at @icao 41st Assembly to a sustainable future with a long-term climate goal... to help put aviation on the path to net zero by 2050."

While it is not a global regulator of the airline industry, ICAO is the UN body that promotes co-operation among member states on air transport. It cannot impose rules on countries, but national governments usually abide by what is agreed at ICAO meetings.

The air transport industry has been under increasing pressure from consumers and scientists to try to find ways to decarbonise air travel for several years, with limited success.

At the ICAO triennial assembly in Montreal, member states finally agreed to support a net zero target for 2050, despite grumbles from China and Russia.

The UK was one of the first countries to include aviation emission in their climate targets in 2021 and helped launch the International Aviation Climate Ambition Coalition at COP26.

They've been amongst 56 countries pushing for an ambitious deal in Montreal.

"This week, members of the International Civil Aviation Organisation agreed to a collective goal of net zero international aviation by 2050 - a historic milestone, not just for the future of flying, but for the wider international commitment to achieve net zero," said Transport Secretary Anne-Marie Trevelyan.

"It represents years of tireless work by the UK and its partners to lead the world towards a clean future for all."

However, environmentalists have major reservations about the agreed resolutions.

"You shouldn't be fooled by the results of this assembly. This isn't going to solve aviation's problem," said Jo Dardenne of campaign group Transport & Environment.

"The only way we're going to solve it is to stop burning kerosene. The way that you stop burning kerosene is by pricing kerosene more effectively and investing in alternative solutions."

At the meeting countries also agreed on changes to a scheme that would deal with a large part of the future emissions from airlines through a system of carbon offsets.

Offsetting is a process where companies or individuals buy carbon credits from schemes such as forestry plantations to cancel out carbon emissions from activities like flying.

ICAO has now agreed that airlines will use the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA).

Under the scheme airlines would agree a baseline year and all future emissions above the level of that period would have to be offset.

Initially they had planned to use an average of flying emissions in 2019 and 2020 - but the onset of the Covid pandemic saw air transport decline rapidly.

While campaigners were delighted with the prospect of a low baseline that would have forced airlines to offset far more of their emissions, the industry baulked.

After discussions in Montreal the threshold has now been set as 85% of 2019 carbon emissions, allowing a higher level of carbon dioxide pollution before airlines must purchase offsets.

In previous analysis, campaigners found that CORSIA would add just €2.40 to the price of a long-haul flight in 2030 to offset passenger's emissions.

They now say that the scheme agreed in Montreal will only cover 22% of future emissions in 2030.

Supporters of the agreement believe that as well as offsetting, airlines will now speed up the development of greener jet fuels, and other technical improvements to decarbonise flying.

"A goal is better than nothing but it is up to member states now to implement the proper regulations," said Jo Dardenne.

"Once this target is there, even if it is non-binding, politically it still forces member states to be ambitious in their climate plans."

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