On a clear day, with the right weather conditions, a portion of the sky busy with commercial flights can become riddled with contrails, the wispy ice clouds that form as jet aircraft fly by.
They might look innocuous, but they’re not – contrails are surprisingly bad for the environment. A study that looked at aviation’s contribution to climate change between 2000 and 2018 concluded that contrails create 57% of the sector’s warming impact, significantly more than the CO2 emissions from burning fuel. They do so by trapping heat that would otherwise be released into space.
And yet, the problem may have an apparently straightforward solution. Contrails – short for condensation trails, which form when water vapor condenses into ice crystals around the small particles emitted by jet engines – require cold and humid atmospheric conditions, and don’t always stay around for long. Researchers say that by targeting specific flights that have a high chance of producing contrails, and varying their flight path ever so slightly, much of the damage could be prevented.
Adam Durant, a volcanologist and entrepreneur based in the UK, is aiming to do just that. “We could, in theory, solve this problem for aviation within one or two years,” he says.
Durant has long studied how atmospheric contaminants affect the health of aircraft engines, and after the 2010 eruption of an Icelandic volcano brought aviation to a standstill, he embarked on a project with Airbus and easyJet to research volcanic ash. In 2013 he founded his own company, Satavia, initially focusing on preserving engines from damaging pollutants like dust, ice and volcanic ash. “Then, Covid shifted the priorities of the whole industry towards sustainability,” he says.
Oversized impact
Satavia pivoted to tackling contrails, by developing a weather prediction model that can forecast the conditions that lead to their formation. Of contrails’ climate impact, “80 or 90% is coming from only maybe five to 10% of all flights,” says Durant. “Simply redirecting a small proportion of flights can actually save the majority of the contrail climate impact.”
The approach Satavia is taking is to target those five to 10% of flights on any given day and modify their flight plans before the aircraft have even taken off. That means changing their altitude or route to avoid flying through parts of the atmosphere which are prone to forming persistent contrails.
“The airlines go ahead and make flight plans as they normally do. But in parallel to that, we analyze their schedule and look at a number of flow trajectories for every single flight,” Durant says. “We end up with a long list of flights of which the top 5% or so have these heavy hitter, long-lived warming contrails. And then we work closely with the flight ops department in the airline to target those.”
The challenge is working around limitations on flight time and fuel consumption. “There are obviously very tight limits on flight time: we have to stay within five minutes of the original intended arrival time. That’s non-negotiable,” Durant says.
As for fuel use, Durant aims to either have no impact on consumption, or keep it within tenths of a percent of the regular flight plan. “If a particular flight has a 0.1 or 0.2% fuel penalty to save potentially hundreds of tons of CO2, that’s fairly negligible but the benefits are huge. There’s a big upside to this if it’s done in the correct way.”
A concerted effort
The first commercial flight utilizing Satavia technology took off in October 2021 and was operated by United Arab Emirates carrier Etihad as part of a program called Greenliner, a testbed for sustainability projects. Since then, Etihad and Satavia have completed dozens of flights, and Satavia is about to start another trial with Dutch flagship operator KLM. “We are going to be actively looking for more airlines in 2023 to work with, as we start scaling up the service that we offer,” Durant says.
In 2021, scientists calculated that addressing the contrail problem would cost under $1 billion a year, but provide benefits worth more than 1,000 times as much. And a study from Imperial College London showed that diverting just 1.7% of flights could reduce the climate damage of contrails by as much as 59%.
According to Marc Stettler, one of the authors of the Imperial College study, who’s not involved with Satavia, the company is on the right track. “I’m all in favor of conducting trials. There are things that we still need to improve and learn, but the industry has started to rightly take this as a high priority, so there’s a number of airlines who are active in this space, including the ones that are working with Satavia,” he says.
However, he adds, the problem requires a concerted effort. “This needs to be collaborative. Satavia are doing good work by initiating these trials themselves and they have to be able to sustain themselves as a commercial organization, but they’re open for collaboration.”
In late November, the Rocky Mountain Institute, a non-profit energy think tank based in the US, launched a cross sector task force to address the contrail problem. Boeing, Airbus and a half dozen airlines including American and United are currently on board, along with researchers and academics. It aims to develop solutions and establish a roadmap to implement them.
Durant is receptive to the idea of collaboration. “We really need action across the industry, we need the operators to come together and work with us. We could do something tangible. We could seriously reduce, say, 50% of the industry’s contrails impact by 2030. That’s totally attainable, because we can do it with software and analytics,” he says.
The challenges ahead, Durant adds, can’t be solved without the involvement of regulatory bodies. “It’s not just about the science – it’s also about how we do this in practice. The rules will need to be updated to allow greater flexibility for both where aircraft fly and how we organize air traffic. And that’s going to be our biggest problem to solve.”