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.
