Contrail mitigation may be the biggest opportunity in climate across all sectors. Contrails are responsible for 1-2% of global warming (maybe even more), and we can eliminate their warming without having to invest billions of dollars, change our behavior, or wait decades for a new technology to develop. Which other big-impact climate solution is so simple, inexpensive, and readily available?
Contrails – short for condensation trails – are the wispy white clouds that planes sometimes leave behind in the sky. When an airplane burns fuel, it releases water vapor and soot particles. If the area that the plane flies through is very cold and very humid, then the water vapor condenses around the soot particles and creates contrails. Most of them disappear again after a few minutes. But if the air at cruising altitude stays cold and humid enough, contrails can linger for hours and spread out to become high-altitude ice clouds – or cirrus clouds – which can grow several kilometers wide and hundreds of kilometers long.
A NASA satellite captures contrails in the skies over the Yellow Sea, between mainland China and the Korean peninsula, on January 24, 2020 (Photo: NASA).
Contrails are responsible for a large chunk of aviation’s climate impact
These big ice clouds act like a blanket on Earth. They reflect some of the sun’s incoming radiation, which gives a cooling effect. But they also prevent Earth’s outgoing radiation from escaping into space, resulting in a net warming effect. The climate impact of these contrails-clouds is at least the equivalent of half of aviation’s CO2 emissions, and it might even be double the CO2 emissions.
Cirrus clouds made from contrails reflect some of the sun’s energy in the daytime but always prevent some of Earth’s heat radiation from escaping into space – resulting in a net warming effect. Contrails are particularly bad for the climate in the late afternoon and at night when there is no heat from the sun to reflect back into space, and the only climate effect the contrail clouds have is acting like a blanket keeping the Earth warm (Graphics: Google Research).
There is a significant difference in how contrails and CO2 emissions affect the climate: CO2 has a very low climate impact, but the impact lasts for centuries and adds up over time. Contrails are just the opposite. They have a very high warming impact, but it only lasts for a few hours. So, if we stop producing warming contrails, we will almost instantly be cooling down the planet. Lowering Earth’s surface temperature is something we desperately need, given that we keep setting new heat records, with July 2023 ranking as the hottest month ever recorded.
The most promising method to mitigate contrails is what more companies and institutions are working on: predicting where and when the very cold and very humid areas in the upper troposphere will appear, then looking at the few planes that are scheduled to fly through those areas and redirecting those flights over, under, or around the contrail-prone weather.
We only need to reroute about 5% of all flights to avoid about 80% of warming contrails (Graphics: Blue Lines).
Only about 1 in 20 flights must be redirected to avoid around 80% of warming contrails. So, 95% of all flights do not need to be changed, making the problem much easier to deal with. The remaining 5% of flights will likely have to spend a little more fuel and CO2 emissions to fly around the contrail weather areas. A recent study by Google Research and Breakthrough Energy showed an investment of 2% extra fuel. Still, when systems are refined, researchers believe we can get that number down to only 0.3% extra fuel. Other studies suggest even lower fuel investments.
”Contrails have been the elephant in the room for the aviation sector for decades.” — Andrew Chen, Rocky Mountain Institute
Why are most airlines not actively working to stop contrails?
All of this sounds almost too good to be true. So why have only about ten airlines publicly acknowledged the climate impact of contrails (Blue Lines track, which airlines publicly announce they are involved in contrails mitigation, trials, or research projects in the Airline Contrail Index)?
The industry has known about the problem for at least 24 years – the first IPCC report about contrails’ huge climate impact came out in 1999. Still, the contrail mitigation systems have only really been developed within the last few years. Until recently, even contrail scientists disagreed that their findings were accurate enough to start implementing action against the warming clouds. Some airlines might claim that we still need more research before taking action, but there is now very little doubt that contrails significantly contribute to global warming.
Another obstacle is that we are so used to talking about global warming in terms of CO2 emissions. Contrails are non-CO2 warming, which is more complicated to understand and has received little attention in the public media and debate.
Also, to avoid making contrails, operators must likely invest a little more money in extra fuel, which will emit a little more CO2 to avoid significant warming from contrails. Most airlines must report their CO2 emissions, so why should they add logistical complexity to their operations, and spend time, money, and CO2 to limit their contrails warming, which they don’t (yet) have to report anywhere? Finlay note: I think the real thing is logistical complexity and additional employee-hours monitoring, tracking and re-defining flight paths. In many cases there is zero or negligible fuel burn penalty. Airlines just don’t want more complexity, regulations and the need to hire or pay more staff.
Along the same lines, the industry has not been keen on admitting that its climate impact might be double that of its CO2 emissions when you add condensation trails. Even if contrail mitigation is an easy and inexpensive solution, it will not eliminate all condensation trails – leaving airlines with a slightly bigger total climate impact – even if they immediately start mitigating contrails as soon as they have acknowledged them.
Ultimately, the primary reason why most airlines ignore the contrail issue is probably the fact that there is no regulation of contrails anywhere in the world. Yet.
But regulation is coming. Recently, the EU announced that airlines – starting in 2025 – must measure, report, and verify the non-CO2 effects of their activities, including contrails. From 2028, the EU plans to implement regulation. Even though this is arguably far too slow a timeline given the urgency of global warming, the EU is the first in the world to introduce the idea of contrails legislation. And the regulatory process should not be an excuse for airlines to wait with implementing contrails mitigation.
In the US, the recently formed Contrails Task Force gathers airlines, aircraft manufacturers, private companies, and scientists to figure out how contrails mitigation could be implemented. There seems to be hope from task force members that getting everyone together in the same room could speed up the process of getting contrails mitigation working in real life.
Connecting contrails to Safe Landing’s four demands of industry leaders:
- Be honest: about the total environmental impact of flying
CO2 emissions are only roughly half of aviation’s climate footprint. Airlines must always include non-CO2 effects like contrails when discussing the environmental impact of aviation.
- Be realistic: about the limits of technology to solve this problem
Changing the hardware and scaling up Sustainable Aviation Fuels (SAF) will take decades, while contrails can be solved in a matter of a few years.
- Be transparent: about future regulations required to reduce emissions
Regulating contrails as soon as possible will massively speed up the adoption of contrail mitigation. Europe is leading the way, but US regulators (and the rest of the world) must also act now.
- Have a plan: that accounts for this and supports workers during any transition
Airlines are pumping billions into SAF and other long-term solutions, but almost nothing is spent on contrails mitigation, which can have a massive and immediate impact. Take a fraction of the resources budgeted for SAF and dedicate it to contrails.
5 myths about contrails and climate change
Myth #1: “We need more evidence about the climate impact of contrails before we can take any action.”
Contrails have been studied for decades, and there is clear evidence that contrails significantly add to global warming. Scientists are working on narrowing down exactly how much contrails are heating the Earth. Contrails are likely as bad for the climate as all the CO2 emissions from aviation, so there are plenty of reasons for acting now.
Myth #2: “People care about CO2 emissions – they don’t know about contrails and radiative forcing.”
This is mostly true – for now. Most of us know that flying makes a huge carbon footprint, but we don’t know that the CO2 emissions are only about half the climate impact of flying. But it is just a question of time before climate activists, campaigners, and airline customers will demand action from airlines to mitigate contrails.
Myth #3: “It’s not yet practically possible to mitigate contrails.”
While there is no big-fits-all solution yet, so many people are working on contrails mitigation: British startup Satavia is flying contrail-free flights with Etihad Airways and KLM. German aerospace center DLR is working on contrail mitigation with Lufthansa. MIT is working with Delta. Breakthrough Energy & RMI work with United Airlines, American Airlines, Alaska Airlines, and others. Flight planning software company Flightkeys has integrated contrail mitigation in their latest version, and more is happening. There are no excuses for airlines not to get involved now.
Myth #4: “Contrails are not regulated anywhere, so there is no reason to do anything.”
So far, regulatory action has focused on de-carbonizing aviation (which is very important but challenging). Still, as contrail-awareness increases, pressure will build on legislators and regulators to act. For airlines, there is a unique possibility for the first-movers to position themselves as the ones caring most about the future of our planet by engaging deeply in contrail mitigation.
Myth #5: “Like most other climate solutions, contrail mitigation is expensive, difficult to implement, and the effect will be slow.”
Contrail mitigation is probably the lowest-hanging fruit in climate. I understand why it might seem too good to be true. To avoid 1-2% of global warming, we need to re-direct a small percentage of planes around the contrail-prone areas in the upper atmosphere. It is easy, cheap (minimal extra fuel burn), and has a near-instant impact on global warming.
(Contrails are NOT the same as chemtrails. Chemtrails are a conspiracy theory. Contrails are science.)
About
This guest blog was written by Joachim Majholm, who is the founder of the US-based non-profit Blue Lines. Blue Lines aims to educate and communicate about contrails and the climate to speed up the road to regulation worldwide. Go to www.blue-lines.org to explore much more about contrails, and sign up for Blue Lines’ newsletter to join the movement and be the first to know about developments in contrails and the climate.
Links to other fun contrails stuff: