A Turning Point in Climate Policy
A new legal analysis highlights an important development for global climate action. Countries are now seen as having a legal obligation to include aviation non CO2 emissions, such as aircraft contrails, in their national climate plans. This step is not just about technical details but about reshaping how international commitments under the Paris Agreement are interpreted.
The Paris Agreement, signed in 2015 by 195 countries, requires each country to submit Nationally Determined Contributions (NDCs). These plans must show how they will reduce greenhouse gas emissions in line with keeping global warming below 1.5 degrees Celsius. Until now, aviation emissions were often seen through the lens of CO2 only. This advice changes that perspective.
Why Non CO2 Emissions Matter
Contrails and other non CO2 impacts from aviation contribute significantly to warming. While CO2 remains the most widely discussed greenhouse gas, scientific evidence has consistently shown that aviation effects beyond CO2 also heat the atmosphere.
Reports from the Intergovernmental Panel on Climate Change as far back as 1999 have flagged these issues. By 2009, the UK Climate Change Committee had already concluded that aviation’s total warming effect is greater than that of CO2 alone. This legal advice now makes it clear that ignoring contrails and other non CO2 effects is no longer an option.
The Legal Obligation Under the Paris Agreement
The Paris Agreement differs from earlier treaties like the Kyoto Protocol. Instead of focusing only on individual gases, it is built around limiting global temperature rise. This means that all forms of warming, not just CO2, fall within its scope.
According to the legal experts, the Agreement leaves no space for excluding aviation or any other sector from climate responsibilities. The principle of precaution also plays a strong role. Even when full scientific certainty is not yet established, countries are required to act. Waiting is no longer justified when risks of irreversible harm are present.
The Limits of Current Aviation Policy
The International Civil Aviation Organization (ICAO) has studied non CO2 effects but has not created binding measures to reduce them. Its main scheme, CORSIA, only covers CO2 emissions above a certain baseline and does not address contrails or other impacts.
The new analysis argues that relying on ICAO alone is insufficient. International law requires countries themselves to include aviation emissions in their NDCs. This includes both CO2 and non CO2 effects.
Why This Matters for National Climate Plans
So far, no country has added non CO2 aviation emissions in its national plan. The European Union and its member states are among the few that even consider international aviation CO2 emissions. This creates a significant gap in global climate policy.
By including contrails and related impacts, countries can close this gap and demonstrate leadership. Even small changes in flight routes could reduce contrail warming quickly and cost effectively. Studies show that less than three percent of flights create eighty percent of contrail warming. Targeting these flights could make a real difference.
The Next Steps Ahead of COP30
The next round of NDCs is due before COP30 in Brazil in 2025. This creates a timely opportunity for governments to expand the scope of their climate plans. Including aviation non CO2 effects would send a clear signal of ambition and responsibility.
For example, the European Union is expected to submit its updated NDC by September 2025. By addressing contrails directly, it could set an important benchmark for others to follow.
The Precautionary Principle in Action
The legal advice also draws attention to a wider legal principle. Under the United Nations climate framework, lack of scientific certainty is not a reason to delay measures. This precautionary approach has been reinforced by international courts. It places a duty on countries to act in advance of full clarity when the risks are serious.
This means aviation contrails should no longer be seen as a secondary issue. They are a central part of the climate challenge and need to be treated as such in every national plan.
A Chance for Progress in Aviation Sustainability
This development is more than a legal technicality. It represents a chance for the aviation sector to align itself more fully with climate science. With effective planning, contrail mitigation can be achieved more quickly than many other forms of emission reduction.
It also highlights the need for stronger collaboration between governments, industry, and sustainability experts. Solutions such as optimized flight paths, fuel strategies, and monitoring systems can help reduce these hidden impacts.
Conclusion
Aviation has often been seen as a hard to tackle sector in the climate transition. The new legal analysis shows that countries must now include both CO2 and non CO2 aviation emissions in their climate commitments. This shift aligns with science, law, and the urgency of global climate goals.
By embracing this obligation, countries can strengthen the credibility of their climate plans and unlock practical solutions for one of the most challenging sectors. With thoughtful planning and international cooperation, aviation can transform from being a climate problem to a sector leading by example in sustainable progress.
Be part of the global conversation on decarbonising flight.
Aviation Carbon 2025 registration is open – reserve your spot now.