Contrails are The Enemy, and There’s a Plan to Stop Them

American, Environment

Other than the wacky conspiracy theory belief that those long streaks of white in the air are actually “chemtrails” where the government is seeding the atmosphere with chemicals, you don’t really hear too much talk about contrails. But guess what? Somebody has been paying attention. American joined work being done by Breakthrough Energy and Google to run a test. Could the airline avoid making contrails and would that help reduce aviation’s impact on climate change? It turns out, the answer appears to be “yes.”

I spoke with Marc Shapiro of Breakthrough Energy, Dinesh Sanekommu on the climate team at Google Research, and Jill Blickstein who is the VP of Sustainability at American to learn more.

As Marc explained to me, this test dates back to a 2020 paper out of Orca Sciences — a research arm of Gates Ventures — saying that you could make changes to 2 percent of aviation and get 80 percent of the potential climate benefit. Orca Sciences started looking into this and eventually it was spun out to Breakthrough Energy, also funded by Bill Gates.

Through its Catalyst program, Breakthrough also funds sustainable aviation fuel work, and American has been involved in that. American and Google had also been working closely together, and the three ended up working on this project jointly.

I couldn’t believe the numbers when they explained the opportunity. Apparently contrails are estimated to cause 1 percent of anthropogenic (read: human-caused) climate change. Even more astounding is that contrails are responsible for 35 percent of aviation’s climate impact, and that may be a low estimate.

How the heck is that possible? Well what happens is that contrails can end up spreading out and turn into cirrus clouds. And it was explained to me that cirrus clouds are far more effective at trapping heat in the atmosphere than CO2. So, if they could eliminate or reduce contrails, that would dramatically reduce aviation’s impact on climate change by reducing the number of cirrus clouds formed.

What the research showed is that contrails form in very wide “ice supersatured regions.” These may be wide, but they are vertically thin. In other words, the altitude range in which contrails will form at any given time is narrow, and that’s what leads us to that headline number up top. If you can move 2 percent of flights mostly up or down a little, that could result in a very big relative change in climate impact. Big numbers with relatively little effort is music to everyone’s ears… if the data can be properly synced up to correctly impact the flight paths.

So, they got to work analyzing all the data to try to see if they could accurately predict what conditions would cause contrails to form. Then with the model in place, the only way to really test this was to create an experiment flying airplanes. And that’s what they did.

The idea was to fly several short-haul flights within North America on narrowbodies. They would look at maps like this one regularly:

This map shows areas where contrails might form across all altitudes. They were looking for places where they could fly a roundtrip flight, and they wanted the potential contrail formation to happen near the end of the outbound. So, let’s say using this map above, they had a Dallas/Fort Worth – Seattle flight. This was ideal, because there was a good chance of contrail formation near Seattle.

They could run the aircraft through the contrail zone on the way up and then on the way back they would try to avoid it. Having it near the initial destination meant there would be a relatively short time period between the two flights going through the same airspace, making the results more valid since weather would have little time to change.

When they had the flights chosen, they would provide the data to the pilots who would use more specific plots to help determine the right routing. I’m not sure which altitude this is exactly, but just pretend it’s FL350 (35,000 feet).

You can see here that up toward Seattle, you might want to fly through at 35,000 feet but then on the return you’d want a different level where contrail formation was not likely.

They would then use Google satellite data after the flight to see if a contrail did form or not in real-time.

There were a total of 22 experiments run, meaning 22 control flights and 22 experiment flights to see if they could reduce contrail formation. Of those 22, in the control group exactly half created a contrail. But in the experiment group, only 4 of them created a contrail. Total contrail kilometers were reduced by more than half from 726 kilometers to only 321. This was a statistically significant result showing real promise for reducing contrail formation.

There were some downsides. For example, if you have to fly at a lower altitude, that means you’re burning more fuel. But in this case they found that these test flights burned 2 percent more fuel. Since it’s already a smaller number of flights that create contrails out of the whole subset, they estimated an overall increase of only 0.3 percent in fuel burn across the network. But there are ways around that as well. Here’s a look at a sample flight:

The fuzzy gray areas are where contrail formation is likely. The original flight plan at 36,000 feet would have been likely to form contrails, but they flew at 32,000 feet until they passed that area and then climbed to 38,000 feet. Overall the impact on fuel burn was minimal.

So, now what? They described this to me as being ready for primetime in years, not decades. But there is more work to be done. In particular, it seems that contrails at night are far worse than those during the day. Those during the day offset the trapping of heat by also reflecting some sunlight back into space. But at night, the clouds are just trapping heat with no offset. They’re also worse in the winter when it’s colder and the likely altitudes for forming contrails drops. They want to test all of this to make sure the results hold up through various scenarios.

In the long run, the idea is to have this data be part of the flight planning process. They hope dispatch can take this into account when looking at aircraft routings. They hope air traffic control can use it in real-time to allow altitude changes. With any luck, these few moves can have a huge positive impact on aviation’s impact on climate change.

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21 comments on “Contrails are The Enemy, and There’s a Plan to Stop Them

  1. I’d really like to believe this… but it’s the first I’ve ever heard of this. Why has it not made news before ? There seems very little discussion about this in public arenas and mass media outlets – it’s the kind of story that credible news outlets really want to talk about but don’t seem to be doing much about it which makes me sceptical. Without widespread reporting, I’m worried this is going to be a bit in the tin foil hat domain.

  2. Interesting. I hear more and more buzz about contrails these days and many recent DOE/DOD awards are about controlling contrails, less on SAF. Thanks for details of the proposed procedure.
    Had two concerns of which one was answered here – clouds supposed to reflect sunlight too that it may not be necessarily bad for global warming perspective, but I haven’t thought about night time! It’s going to heat up the ground at night esp if contrail worsens at night. But I still doubt how come the impact could be as high as 35%, when emitted CO2 remains in the air for many years while cloud/contrail is removed within an hour or two.

    1. You’re absolutely right. CO2 stays in the atmosphere for decades – even centuries, but has a very low climate impact (which of course accumulates over time to become significant). Contrails have a very short life span of a few hours, but their climate impact is very high. This is also why, if we stop making warming contrails, it should immediately cool down the planet a bit. See more at

  3. I’d take any research funded by the Gates Foundation with a grain of salt.
    Just wait, they’ll recommend ‘contrail charges’ on commercial tickets, but private jets will somehow be exempt.

    1. I can understand why people think they are hypocrites but I do think their health initiatives deserve praise. There aren’t many out there that can claim to be the second biggest funder of the WHO. One could perceive that as a conflict of interest but they are definitely investing in eradicating certain illnesses.

  4. It’s quite true that this (contrail research) is a “thing”:

    I vividly recall those days right after 9/11 and how quiet it was – and how unique to see the sky with not one aircraft in it. A sight that I may never see again. As a climatologist, I couldn’t help but wonder if the effects would be studied (and, of course, they were).

    Whether this particular experiment takes us anywhere is very questionable. Good effort, but not sure that it’s enough to move forward with any changes. And, things like safety and economics will be quite a bit higher on the decision tree than whether we make contrails, which is another barrier to this being implemented on a grand scale. My final concern comes from absolute skepticism of anything funded by Bill Gates or any of his various funding entities. This guy is a megalomaniac and cannot be trusted.

    All that said, there’s probably more net benefit to finding a way to significantly reduce contrail than there is to paving massive tracts of land with solar panels or scarring square miles of land (or sea) with wind turbines.

  5. I love how the mention of Bill Gates bring out all the conspiracy theorists. I think he does some great work funding initiatives like seeds that hold up better in drought conditions like Africa and others to help people. Think about the good you can do for humanity instead of complaining, guys.

    1. One would think all the microchips he injected in everyone with the Covid shots would have enabled him to better control the naysayers. :)

  6. For those who are Gates-averse, the dude who wrote this paper is funded by the Royal Society (UK): – the study also included input from multiple airlines, even though they are contributing data/information that paints aviation in a negative light. This is an interesting area of study and definitely worth exploring more.

    Dr Gryspeerdt is faculty at Imperial College London – also not a shabby institute:

    1. “Contrails are The Enemy, and There’s a Plan to Stop Them” wrights Cranky, & as soon as I saw the name Bill Gates it was only a matter of time until the conspiracy theorists would come out of the baggage compartment.

      The research is in it’s infancy & it’s going to take time to see what value it has if any.

  7. The article did a fine job of describing the success of the experiment in controlling formation of contrails but, it did not even touch upon the biggest question of what effect contrails actually might have on the environment. The fact is that no one yet knows. The answer is likely to be, “it depends”.

    In some situations such as on a bright day, contrails will reflect much of the heat from the sun back out into space and is likely to have an overall cooling effect on the environment. The same contrail at night time might have a reverse effect by reflecting the heat radiated by the surface of the earth back to earth (thus, the greenhouse effect).

    I want to see more research being done to study the overall effect of contrails on the environment under different situations instead of spending all of our efforts on reducing contrails before we even know if it is good or bad for the environment. Enough of this herd mentality! This is why margarine was good back when but is now bad. Poly unsaturated fat was good but now bad. Instead, saturated fat is now good. Before, more exercise the better but now evidence suggests that low impact exercise is the best for health, low rate of injury and has life-extending benefits.

    1. Frank, did you even bother to actually read the article??

      Cranky specifically discussed the difference between day and night effects, and also talked about how additional tests will be conducted to see how the results vary under different scenarios.

  8. “Poly unsaturated fat was good but now bad. Instead, saturated fat is now good.” Not quite. Saturated fat is now not as bad as was thought, but polyunsaturated is still healthier. Not sure which of those fats leads to greater contrail generation – maybe George Soros can fund that study…

    1. Soros is too busy setting up drag queen story hours at nursery schools to fart around with contrails.

      1. My bad, you’re right. Drag queen story hours WAY more important than dealing with environmental effects of contrails, and Soros knows this, hence his bank balance is better than mine.

  9. Interesting story, as usual!
    I live under the downwind leg of the approach pattern to ORD. Aircraft pass over at about 3,000 feet, and I have to clean my patio table every day – and I’m amazed at how much “soot” I clean off it. In contrast, after 9/11 my table was clean! Clearly, I don’t need much analysis to figure it out, and so the effect of contrails is certainly worthy of study.
    Re: Gates. Anyone who knows anything about the eradication of Polio will recognize that a lot of that work was because of Gates. That’s an absolute scourge of a disease – largely eradicated. Does he get it right – all the time? Do you…..???

  10. I think this is something I’d love to see really play out and see the results. Nothing like a good hypothesis that could actually help us slow down planetary evolution.

    I just wonder if this is just going to validate all of the #avgeek memes that make fun of the “chem trails” buttons in the cockpit…

  11. The whole thing is assumptions based upon other assumptions. No one knows what percentage, if any, of warming is purely anthropogenic. It’s not ascertainable. But somehow we’re supposed to believe that these guys correctly figured out that contrails are directly responsible for 1% of that unascertainable figure.

    Gotta salute them for the “innovation” though. The study could help assist with more taxpayer funds being directed to research this issue further, and then one day, if we’re lucky, there can be brand new taxes and surcharges based upon that research. What a dream.

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