Contrails could be responsible for up to 2% of all global warming, and yet how they’re formed and how to mitigate them is barely understood by major airlines.
That may be changing.
Delta and MIT just announced a partnership to test how to mitigate persistent contrails. Those trails may look innocuous, but their climate impact is outsized, and as of yet unaddressed.
Fortunately for the aviation industry, preliminary research and modeling indicate that it’s possible to almost completely avoid contrail formation through some very simple — and fuel-efficient — rerouting. That theory is currently being put to the test, and, if the partnership’s experimental flights go according to plan, Delta may start implementing flight changes to cut down on one of the industry’s largest climate impacts. Unlike carbon dioxide, which can stay in the atmosphere and exert a warming influence for centuries, contrails have a fairly quick and direct impact. Reducing them could provide near-term climate relief as the industry works to decarbonize over the long haul.
“If our hypotheses really prove to be true, we could almost immediately avoid any of the climate impacts of the persistent contrails,” Pam Fletcher, Delta’s chief sustainability officer, told Protocol.
Using satellites and machine learning, researchers from MIT’s Laboratory for Aviation and the Environment have been working to determine the regions and altitudes in which contrails form and a system for feeding that information to Delta’s pilots so that they can route planes to avoid them.
The partnership, which began last year, has already tested the system with about 40 experimental and, according to Steven Barrett, “very targeted” flights, in which pilots flew through regions where contrails are likely to form and changed altitudes to verify that the satellite estimates were accurate.
Right now, Barrett, a professor of aeronautics and astronautics at MIT and director of the lab, said it’s developing a larger-scale trial to gain “real statistical confidence” that the system works and pilots are able to successfully avoid creating contrails. In addition, the team is working on measuring and validating how much fuel the flight changes will burn. Estimates indicate that the tweaks would only use up to 2% more fuel, which would make the changes worth it for both the bottom line and the climate.
“Almost all the knowledge to date is based on models,” Barrett said. The hope for the flight tests is that they will prove that contrails can be avoided, as well as measure how much warming influence contrails have at different times of day. (Nighttime contrails are purely warming, whereas daytime contrails can be warming or cooling, depending on a number of factors.)
Most of the attempts at contrails avoidance to date have been based on weather forecasting models, Barrett said, which aren’t as accurate as satellite data combined with machine learning. Eventually, the hope for the research team is that that satellite data will be used to adjust flight paths in real time, and forecast resulting fuel burn changes so that flight teams can be prepared, he said.
Delta and MIT are open sourcing the results of their research, which they hope other airlines will use to reduce their own contrails.
If things go according to plan, the commercial aviation sector could begin taking contrail-avoiding measures almost immediately, which is huge for an industry whose path to decarbonization still has many other hurdles. Barrett pointed to sustainable aviation fuels as a counterpoint: SAFs would cost quite a bit more than traditional jet fuel. Contrail avoidance, on the other hand, can cut down on warming in a way that’s much easier and, critically, cheaper.
“We think it can be achieved with fairly small adjustments,” Barrett said of avoiding contrail-forming regions. “So far, the science is very encouraging.”
For its part, Delta is “very interested in” implementing altitude and routing changes once the flight trials produce “proven, validated results,” Fletcher said.
“This is beautiful, because if we can make it work, we can make it work now,” she said.