Over the next two weeks, government officials, airlines and environmental groups are meeting in Montreal to agree a deal which they hope will allow global climate action for the aviation sector to finally take off.
This is important because if the aviation sector were a country, it would rank seventh in the world for its greenhouse gas emissions, contributing to around 2% of carbon emissions. What's more, without action the sector's emissions are set to balloon by 300% above 2005 levels by 2050. In short, aviation has an emissions problem.
The good news is that the UK Government is pushing hard to secure a global deal for aviation pollution. The result could be that airlines have to offset emissions from their flights on international routes (though they will only have to offset any growth in emissions after 2020 to meet the UN's target).
The bad news is that the Government could follow that up with a decision to build a new runway at Heathrow. The result of that decision would be that the CO2 emissions from UK flights would fly sky high above the level they should be under our national climate targets.
The industry argues that as aviation is a global industry, we should act globally to avoid any individual countries being put at a competitive disadvantage. However, global action requires support from countries all over the world, some of which are reluctant to commit to any action on climate change if it looks as though it could restrict their economic development, including their aviation sector. This means inevitably ambition is lost as compromises are made.
The outcome for the deal being discussed at the UN aviation body, ICAO, over the next two weeks is that not all international aviation routes, and their associated emissions, will be covered. Even if all countries sign up voluntarily, offsetting the growth of emissions in the aviation sector after 2020 is not even close to the scale of ambition of the Paris Agreement to limit global warming to well below 2C. Hopefully, the ICAO agreement will include regular reviews to consider whether the cap should be made progressively tougher to deliver deeper cuts, but the likely success of future negotiations is difficult to predict.
Even if the best possible deal is agreed over the next two weeks, it will only be the beginning of a plan to address aviation's emissions problem. More action is needed to show the same ambition that saw States commit to the provisions of the Paris Agreement.
The aviation industry continues to make gains in technology and the use of biofuels could have a limited role in reducing emissions. Operational improvements (literally flying planes in straighter lines) could also reduce emissions. However, the sector has an ambitious target of making efficiency improvements of 1-2% per year while air traffic is forecast to grow globally at close to 5% per year, leaving a major gap in emissions.
The UK Government hopes the offsetting scheme will provide a solution, but we know expanding Heathrow or Gatwick would lead to an increase in emissions from aviation while there is currently no plan to demonstrate the additional measures that will be needed to ensure UK aviation emissions remain under control and don't threaten delivery of the Climate Change Act.
The uncomfortable truth is that governments across the world will need to face the fact that aviation can't have unlimited growth and will need to look at ways of managing demand to sustainable levels. That's likely to require managing airport capacity and taking action on the tax breaks and subsidies the industry currently enjoys.
If the UK Government faces up to this truth and treats the likely deal at ICAO as only one part of the solution, action on aviation emissions could truly take off.