Here’s the question:
Is progress on contrails avoidance limited more by the ability to avoid contrails or the motivation to actually do it?
It is sometimes claimed that contrails avoidance is a cheap and easy solution to a large amount of climate change, and that progress is held back by lack of public awareness and pressure on the aviation industry. If true, that would be very important, and it would suggest high value in public awareness campaigns. It may even be the case that contrails avoidance is the world’s most underrated climate solution and in urgent need of further attention.
However, it is also sometimes claimed that contrails avoidance is instead held back by the uncertainty in the science of contrail forecasting and the logistical difficulty of avoiding contrails across the aviation sector. If that is true, there may still be a role for awareness campaigns, but there needs to be a focus on improving the science and logistics.
Background – Contrails and Climate Change
Contrails, or condensation trails, are the clouds formed by airplanes. They are perhaps best known for their association with the baseless chemtrails conspiracy theory, but here we are talking about the actual science, as discussed, for example, in this recent report by the US National Academies.
Contrails are made of water vapor frozen into tiny ice crystals. Water vapor is a greenhouse gas, and contrails contribute to climate change. Researchers (e.g. Teoh et al. 2024) estimate contrails as causing about 1-2% of total climate change, about the same as the climate impact of CO2 emissions from airplanes burning fuel. For perspective, this is comparable to the total climate impact of a country like Japan, Germany, or Mexico.
There is one important difference between the climate impacts of contrails and CO2. Whereas contrails fade away within a few hours or so, CO2 stays in the atmosphere for much longer, potentially even centuries or more. Avoiding contrails provides sharp, immediate climate benefits, whereas reducing CO2 emissions provides longer-lasting benefits. In situations involving a tradeoff between reducing contrails and reducing CO2 emissions (discussed further below), resolving the tradeoff depends on judgments about near-term vs. long-term climate change, such as in the use of a discount rate.
There are three basic ways to reduce the climate impact of contrails. One is to fly less. This has the added benefit of also avoiding CO2 emissions and other harms of air travel, such as local air and noise pollution. The second is to redesign aircraft and fuels. For example, some work on cleaner fuels (“sustainable aviation fuel”, e.g. Grimes and Alvarez 2025) finds that this also reduces contrails. The third is to shift airplane flight paths, which merits further elaboration.
Shifting Flight Paths to Avoid Harmful Contrail Formation
As one can readily observe by looking at planes in the sky, contrails only form on some flights. This is because contrail formation requires specific atmospheric conditions, especially cold air and high humidity. Furthermore, some contrails are not harmful for climate change. For example, nighttime contrails are more harmful because during the day, clouds (being white) reflect some incoming sunlight away from the surface, which cools the surface, counteracting some or all of the warming effect. Because of this, to avoid harmful contrails, we only need to shift some flights. One recent study (Teoh et al. 2024) found that just 2% of flights cause 80% of the climate impact of contrails.
Additionally, contrail-forming regions of the atmosphere tend to be horizontally wide but vertically shallow. Because of this, to avoid contrails, we only need to shift flight paths up or down in the sky a little bit.
Small shifts in flight paths for a small portion of flights: this is the basis for contrail avoidance being a cheap and easy climate solution. One recent study (Frias et al. 2024) found that it would increase financial costs by just 0.08% and fuel usage (for slightly longer flight paths) by 0.11%. In comparison, sustainable aviation fuel is generally found to be much more expensive, potentially even around 100 times more expensive to achieve the same climate benefit.
Because contrail avoidance can entail longer flight paths and therefore more fuel usage, it does come with a tradeoff between the climate impacts of contrails and CO2. Environmental economists (Johansson et al. 2025) have sought to evaluate those tradeoffs using standard climate economic modeling tools, including discount rates. This type of analysis was the focus of my Ph.D. research, which left me with a generally negative impression of this line of modeling. I urge caution in the use of such tools for contrails avoidance. However, these details may not matter for many actual contrail avoidance decisions if they involve a large amount of contrail warming and a much smaller amount of CO2 warming.
Public Awareness and Pressure on the Airline Industry
Public awareness of contrails and climate change appears to be extremely low.
As one anecdote, despite my own research background in climate change, I only learned about contrails a few weeks ago when I saw it in this video:
The video is by Simon Clark, an excellent video creator who has a Ph.D. focused on climate science. In his video, he says he only learned about contrails from this blog post, published a few months earlier by Hannah Ritchie. The fact that two climate experts—Simon Clark and myself—only just recently learned about contrails speaks to the low awareness of it.
I haven’t seen any formal studies of public awareness of contrails, but I can provide some more substantive evidence indicating that awareness is indeed very low. First, the environmental charity group Giving Green has a systematic survey of major climate solutions; in it, contrails is one of only two solutions (along with microplastics) flagged as limited by low awareness. Second, I reviewed attention to contrails in major environmental nonprofits and media outlets (as detailed here). None of them have made any significant effort to raise public awareness about shifting flight paths to avoid contrails. Some nonprofits have behind-the-scenes technical work, in particular RMI and WWF, and there was some good coverage by Canary Media here and here. However, overall, I was struck by how little attention there was.
Hannah Ritchies’ blog post hypothesizes that progress on contrail avoidance is limited mainly by lack of awareness. Her reasoning is that it’s so cheap and easy, airlines would already be doing it if only there was some pressure on them. Without public pressure, they would rather make a few extra bucks—the cost of contrail avoidance might be low, but it’s not zero. Indeed, the aviation industry has lobbied (unsuccessfully) against contrails policy in the EU. However, there’s also another possible explanation.
Scientific Uncertainty and Logistical Difficulty
Shifting flight paths to avoid contrails may be cheap, but it might not be so easy.
Successful contrail avoidance requires two things: scientific forecasts of regions where contrails would form and logistical implementation of flight path shifts to avoid those regions. Both of those may be significant impediments.
On the science, there may be a shortage of data for forecasting, with some models only making correct forecasts 20% of the time, and different models yielding different predictions. Interaction effects between contrails and natural clouds further complicates the challenge of forecasting contrails that will be net harmful for climate change.
On the logistics, in principle contrail avoidance should be feasible. The aviation sector already adjusts flight paths based on forecasts of atmospheric conditions in order to avoid turbulence; contrail avoidance is fundamentally similar. However, in practice, so far contrail avoidance has proven difficult to implement at scale.
In the EU, the air traffic control agency Eurocontrol is tasked with contrail avoidance. During summer 2025, they paused their contrail program. Summer is Europe’s peak travel season and Eurocontrol couldn’t keep up with the logistics of contrail avoidance with so many flights in the sky. Note that currently, the EU is the only place with a contrail avoidance policy, so other jurisdictions presumably have even weaker contrail avoidance capabilities.
So, Which Is It?
If contrail avoidance is limited mainly by science and logistics, then there may be less need for public awareness. That could be true even if awareness is indeed very low, as it appears to be. Alternatively, if the science and logistics is good enough, and progress is instead held back by a reluctant airline industry and/or lack of attention from policymakers, then public awareness and pressure could make the difference.
In my research on contrails, I have not been able to resolve this question. I haven’t been able to find anything in the public record that addresses it. And so, instead of providing an answer, I can only raise the question in hopes that doing so will prompt further inquiry.
There may be a role for both improved ability to avoid contrails and improved awareness and motivation. Even if the science and logistics is holding us back, it still can’t hurt to have greater awareness—contrails are important, and that alone is reason enough to have more awareness. Furthermore, public pressure could be mobilized to advance work on the science and logistics. Even if contrail avoidance might not be cheap and easy right now, it has strong potential to get there.
As a matter of both ethics and political strategy, it is important for environmental movements to prioritize solutions that are cheap and easy. Some prominent solutions are unpopular due to the costs they impose on people, for example a carbon tax. Others are unpopular due to them being perceived as unpleasant, such as asking people to drive less in areas lacking good transit. For contrail avoidance to potentially be both cheap and easy, it is worth pursuing further.
I explore these themes further in a video on my personal (non-GCRI) YouTube channel:
The video critiques and builds on Simon Clark’s video while attempting to further raise awareness about contrails, though so far my video has reached a much smaller audience. I also have detailed research notes in a post to my Patreon account. The post is written to accompany my video, and it can also serve as a resource for further work on contrails, especially work on public awareness.
Image credit: Adrian Pingstone Arpingstone
