The aviation tech on the trail of saving the planet

Stripy cloud formations left in the wake of aeroplanes may look picturesque, but are in fact thought to trap heat in the earth’s atmosphere. Scientists believe that minimising or even eliminating them will help to slow climate change.

Battling the formations – known as contrails – would mean changing flight routes and sometimes burning more fuel. While such efforts could slash the aviation industry’s climate impact, already cash-strapped airlines will likely need incentives for them to materialise.

Adam Durant, founder and boss of aviation-tech firm Satavia, thinks he has a solution: work out how much eliminating the contrail of a flight helps the planet and give the airline a carbon credit which they can sell.

Contrails, also called condensation trails or vapour trails, form when water vapour produced by jet engines condenses in cold, humid air, often around the soot particles which jet engines can also emit. They can last from seconds to hours – the latter are considered the problem.

The trails are worse for the environment than regular clouds because they are formed high up in the atmosphere and are made of ice, rather than water vapour.

While they can reflect some of the sun’s radiation back into space, which is helpful when trying to mitigate a warming planet, contrails are far better at reflecting heat back to earth. This warming influence is why scientists are concerned.

Aviation contributes about 2.5pc to global carbon dioxide emissions from human activity, according to Bernd Karcher, research physicist at the German Aerospace Center, and the latest research suggests contrails have a similar climate impact.

The reason CO2 has been higher up the agenda, as opposed to emphasising the need to stop contrails, is that the impact of the gas is longer-lasting.

Stop contrails tomorrow and the effect ends. Stop CO2 production and the previous gas remains in the atmosphere. But the vapour trails are still something to be tackled, argues Marc Stettler from the department of civil and environmental engineering at Imperial College.

“All of the CO2 that we've emitted into the atmosphere from flying will remain, and any CO2 we emit tomorrow will remain in the atmosphere for hundreds of years, if not thousands of years. So there's a very different timescales to the problem and the solution,” says Stettler.

“On the other hand, the contrail effect is very short-lived in the sense that if we stopped producing contrails tomorrow, we could get rid of that [effect].”

The trick is to avoid flying in ice supersaturated regions - the area in which these clouds form.

Flight plan overhaul

This is what Cambridge-based Satavia - which says it aims to prevent 60pc of aviation's climate impact - thinks it has cracked. Durant’s firm is working with UAE carrier Etihad to predict where these regions are and modify a small number of flight plans to avoid them, by changing the altitude and route.

“We want to also provide an incentive for the aircraft operators, commercial incentives. So we're working on a carbon credits method. We'd like to get this accredited,” said Durant, a scientist who started his commercial career developing a volcanic ash detector for the Norwegian Institute for Air Research.

Durant, who founded Satavia eight years ago to make software to help airlines and aircraft makers understand their climate impact, says he will need to quantify how much carbon equivalent a new flight plan saved and estimate what that could be worth as a carbon credit.

If the airlines can gain carbon credits from avoiding making contrails, then hiring Satavia to help them do this should cost them nothing, he argues. A valuable selling point to an industry which has been hit by more than $200bn of losses by the pandemic, according to the International Air Transport Association (IATA).

“We hope within 12 months, we can start trading carbon credits” and attract new operators, he said. “It should become a no-brainer for the operator because there won't be any additional costs. They get a share of carbon credits created, they’ll be able to say that they are reducing their non-CO2 climate impact.”

In a recent test, a flight used an extra 100kg of fuel – which might produce 316kg of carbon dioxide – in order to save the equivalent of 64 tonnes, or 64,000kg, of CO2 in contrail effects, he estimates.

But challenges remain. Durant is up against a highly regulated industry where altering routes is difficult.

“We wouldn't be able to change every flight we wanted to there'll be some scenarios where the rules don't permit it. There's congestion, external factors out of our control, like war or natural hazards. But we will take all of that into account,” he says.

Contrail fail

And his plan has its critics. Professor David Lee of Manchester Metropolitan University says Satavia should publish its methods and open them up to peer review.

Lee’s work suggests that contrails’ climate effect is 65-70pc greater than CO2. He has said that mitigating these effects is “highly desirable”, but that today's knowledge of the science makes it very hard to be sure you are helping rather than harming the planet.

“If you can't predict where this happens with accuracy, then you're in great danger of making things worse,” says Lee, adding that it might lead to burning more fuel for no reason, or avoiding an area that would not have produced a contrail and head for one that does.

“We just don't have the observations that allow us to understand exactly how these ice supersaturated areas occur on the fast moving timescales that they do,” he says. Instead, he argues that focusing on cutting carbon emissions is probably a better idea: “You can fix a lot of the problem just by looking at CO2.”

Durant says his company is a commercial enterprise and not an academic organisation that publishes its methods.

His team has been working on modelling contrail formation for three years after helping Rolls-Royce find a way to stop ice crystals forming on its engines when cruising at high altitudes.

“We got very good at predicting water in the atmosphere, which is exactly what they're talking about,” Durant says.

“We calculate for the entire domain, which might be all the way from the Middle East to the North Atlantic, data on over 200 parameters at millions of locations in our model, every 30 seconds. So we're actually able, to a certain extent, capture those quite fast moving changes.”

Another bone of contention is the soot aero engines produce when burning jet fuel. This is thought to help the ice crystals form and moving to artificial fuel cuts the soot and perhaps the problem, according to Karcher.

But that thesis ignores the sheer cold of the environment in which the clouds form, says Durant. “I think that's a myth that needs debunking, or at least needs more scientific research.”

A move to hydrogen in aviation will also need careful monitoring of contrail formation because of the amount of water created from burning - potentially providing the perfect conditions for contrails to form.

While Lee and Karcher are sceptical over Satavia’s plans, Stettler says it is worth a shot.

“There's differing views on how quickly contrails could be avoided by navigational avoidance - I think it's fair to say that everybody understands weather forecasts aren't perfect,” he says. “My view is that you shouldn't stand in the way of doing a trial [and] working towards implementing it.”