Changing flight paths could slash aviation’s climate impact, study suggests

 ‘The climate opportunities and risks of contrail avoidance.’ 

University of Cambridge

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Small changes to aircraft flight paths to avoid the atmospheric conditions that create condensation trails – known as contrails – could reduce aviation’s global warming impact by nearly half, a new study suggests.

The study, led by researchers at the University of Cambridge, suggests that changing cruising altitude by a few thousand feet, either up or down, could prevent contrails from forming. Reducing or avoiding contrail formation in this way would also be faster and cheaper than other climate mitigation measures for the aviation industry, since the practice can be adopted with existing aircraft and fuel.

However, the researchers say that time is of the essence, and that the sooner airlines adopt contrail avoidance policies, the bigger the positive climate impact will be. Their results are reported in the journal Nature Communications.

Contrails are the thin white streaks seen behind aircraft flying at high altitude, and form when hot exhaust gases mix with cold, humid air at cruising altitude. Under the right conditions, the water vapour freezes into ice crystals, forming clouds that can persist for hours.

Contrails also trap heat in the atmosphere. Aviation contributes around 2–3% of global carbon dioxide emissions, but its total climate impact is larger because of non-CO₂ effects such as contrails. Interest in contrail avoidance has grown rapidly in recent years as governments and airlines search for ways to reduce aviation’s climate impact while the sector transitions to lower-carbon fuels.

“Contrail avoidance can often be as simple as changing the flight paths,” said lead author Dr Jessie Smith, from Cambridge’s Department of Engineering. “Often it’s even simpler than that – just moving slightly to a higher or lower altitude to avoid the areas of the atmosphere where contrails form.”

Smith and her colleagues modelled how altitude adjustments for contrail avoidance could affect aviation’s overall climate footprint. They found that such a programme, phased in between 2035 and 2045, could recover around 9% of the temperature budget the world has left before breaching the Paris Agreement’s 2°C limit.

However, they also found that if no action is taken, by 2050 aviation contrails will have added around 0.054°C of warming — 36% more than the warming attributable to aviation CO₂ over the same period.

“What surprised me was how quickly the temperature saving could be made,” said Smith. “Over a decade, you can take a really big chunk of aviation’s warming impact out very rapidly. That's unusual in climate science, where most changes take a very long time.”

The researchers also found that while rerouting aircraft can increase fuel use slightly, the reduction in warming from fewer contrails would more than offset the extra carbon dioxide emissions.

Implementing contrail avoidance would require airlines and air traffic controllers to adjust routes dynamically based on atmospheric conditions. Some aviation experts have raised concerns about whether such changes could increase workload for air traffic management systems, but the researchers say the adjustments required may be relatively modest.

Flights already alter their routes or altitude to avoid turbulence or bad weather, meaning similar systems could potentially be used to avoid contrail-forming regions.

“It's an operational change, not a technological one,” said Smith. “You don't need to modify aircraft. You just need to work out how it will operate, and then the system is already built for it — pilots do these manoeuvres all the time. That’s why we have more hope for this than for other interventions like sustainable aviation fuels, which face enormous infrastructure and supply-chain hurdles.”

Using a climate model that tracks temperature responses across 10,000 simulated scenarios, the researchers found that beginning contrail avoidance in 2035 rather than 2045 produces a temperature reduction at 2050 that is equivalent to roughly a 78% improvement in effectiveness. “In other words, waiting a decade has roughly the same effect as making the programme almost five times less efficient,” said Smith.

While more work is needed to improve forecasts of the atmospheric conditions that cause contrails and to better understand their climate effects, the researchers say that imperfect avoidance — even at 25% effectiveness — still delivers a meaningful climate benefit, and that starting early matters more than waiting for the technology to be perfected.

Scaling up contrail avoidance will require coordination from pilots, air traffic controllers, weather forecasters and policymakers, however. “The first step is demonstrating this works on a large scale through testing,” said Smith. “Once that's done, the policy can follow. But the modelling shows clearly that you do not want to wait for perfect conditions before you begin.”

Smith said the findings show the approach could play a major role in aviation’s climate strategy. “We’re not saying it solves everything,” she said. “But it could make a very big difference.”

Reference:
Jessie R. Smith et al. ‘The climate opportunities and risks of contrail avoidance.’ Nature Communications (2026). DOI: 10.1038/s41467-026-68784-8

 

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Journal

Nature Communications

DOI

10.1038/s41467-026-68784-8 

Article Title

The climate opportunities and risks of contrail avoidance

Article Publication Date

2-Mar-2026

CONTRAILS REAL;  CHEMTRAILS NOT SO MUCH

Study: More eyes on the skies will help planes reduce climate-warming contrails

Images from geostationary satellites alone aren’t enough to help planes avoid contrail-prone regions, MIT researchers report.

Massachusetts Institute of Technology

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image: 

Four research figures show how contrails appear in two satellite views (left) and two photographs taken from the MIT Green Building.

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Credit: Courtesy of Prakash Prashanth, Marlene Euchenhofer, et al

Aviation’s climate impact is partly due to contrails — condensation that a plane streaks across the sky when it flies through icy and humid layers of the atmosphere. Contrails trap heat that radiates from the planet’s surface , and while the magnitude of this impact is uncertain, several studies suggest contrails may be responsible for about half of aviation’s climate impact.

Pilots could conceivably reduce their planes’ climate impact by avoiding contrail-prone regions, similarly to making altitude adjustments to avoid turbulence. But to do so requires knowing where in the sky contrails are likely to form. 

To make these predictions, scientists are studying images of contrails that have formed in the past. Images taken by geostationary satellites are one of the main tools scientists use to develop contrail identification and avoidance systems.  

But a new study shows there are limits to what geostationary satellites can see. MIT engineers analyzed contrail images taken with geostationary satellites, and compared them with images of the same areas taken by low-Earth-orbiting (LEO) satellites. LEO satellites orbit the Earth at lower altitudes and therefore can capture more detail. However, since LEO satellites only snap an image as they fly by, they capture images of the same area far less frequently than geostationary (GEO) satellites, which continuously image the same region of the Earth every few minutes. 

The researchers found that geostationary satellites miss about 80 percent of the contrails that appear in LEO imagery. Geostationary satellites mainly see larger contrails that have had time to grow and spread across the atmosphere. The many more contrails that LEO satellites can pick up are often shorter and thinner. These finer threads likely formed immediately from a plane’s engines and are still too small or otherwise not distinct enough for geostationary satellites to discern.

The study highlights the need for a multiobservational approach in developing contrail identification and avoidance systems. The researchers emphasize that both GEO and LEO satellite images have their strengths and limitations. Observations from both sources, as well as images taken from the ground, could provide a more complete picture of contrails and how they evolve. 

“With more ‘eyes’ on the sky, we could start to see what a contrail’s life looks like,” says Prakash Prashanth, a research scientist in MIT’s Department of Aeronautics and Astronautics. “Then you can understand what are its radiative properties over its entire life, and when and why a contrail is climatically important.”

The new study appears today in the journal Geophysical Research Letters. The study’s MIT co-authors include first author and graduate student Marlene Euchenhofer, undergraduate Sydney Parke, Ian Waitz, the Jerome C. Hunsaker Professor of Aeronautics and Astronautics and MIT’s vice president of research, along with Sebastian Eastham of Imperial College London.

Imaging backbone

Contrails form when the exhaust from planes meets icy, humid air, and the particles from the exhaust act as seeds on which water vapor collects and freezes into ice crystals. As a plane moves forward, it leaves a trail of condensation in its wake that starts as a thin thread that can grow and spread over large distances, lasting for several hours before dissipating. 

When it persists, a contrail acts similar to an ice cloud and, as such, can have two competing effects: one in which the contrail is a sort of heat shield, reflecting some incoming radiation from the sun. On the other hand, a contrail can also act as a blanket, absorbing and reflecting back some of the heat from the surface. During the daytime, when the sun is shining, contrails can have both heat shielding and trapping effects. At night, the cloud-like threads have only a trapping, warming effect. On balance, studies have shown that contrails as a whole contribute to warming the planet. 

There are multiple efforts underway to develop and test aircraft contrail-avoidance systems to reduce aviation’s climate-warming impact. And scientists are using images of contrails from space to help inform those systems. 

“Geostationary satellite images are the workhorse of observations for detecting contrails,” says Euchenhofer. “Because they are at 36,000 kilometers above the surface, they can cover a wide area, and they look at the same point day and night so you can get new images of the same location every five minutes.”

But what they bring in rate and coverage, geostationary satellites lack in clarity. The images they take are about one-fifth the resolution of those taken by LEO satellites. This wouldn’t be a surprise to most scientists. But Euchenhofer wondered how different the geostationary and LEO contrail pictures would look, and what opportunities there might be to improve the picture if both sources could be combined. 

“We still think geostationary satellites are the backbone of observation-based avoidance because of the spatial coverage and the high frequency at which we get an image,” she says. “We think that the data could be enhanced if we include observations from LEO and other data sources like ground-based cameras.”

Catching the trail

In their new study, the researchers analyzed contrail images from two satellite imagers: the Advanced Baseline Imager (ABI) aboard a geostationary satellite that is typically used to observe contrails and the higher-resolution Visible Infrared Radiometer Suite (VIIRS), an instrument onboard several LEO satellites. 

For each month from December 2023 to November 2024, the team picked out an image of the contiguous United States taken by VIIRS during its flyby. They found corresponding images of the same location, taken at about the same time of day by the geostationary ABI. The images were taken in the infrared spectrum and represented in false color, which enabled the researchers to more easily identify contrails that formed during both the day and night. The researchers then worked by eye, zooming in on each image to identify, outline, and label each contrail they could see. 

When they compared the images, they found that GEO images missed about 80 percent of the contrails observed in the LEO images. They also assessed the length and width of contrails in each image and found that GEO images mostly captured larger and longer contrails, while LEO images could also discern shorter, smaller contrails. 

“We found 80 percent of the contrails we could see with LEO satellites, we couldn’t see with GEO imagers,” says Prashanth, who is the executive officer of MIT’s Laboratory for Aviation and the Environment (LAE). “That does not mean that 80 percent of the climate impact wasn’t captured. Because the contrails we see with GEO imagers are the bigger ones that likely have a bigger climate effect.” 

Still, the study highlights an opportunity.

“We want to make sure this message gets across: Geostationary imagers are extremely powerful in terms of the spatial extent they cover and the number of images we can get,” Euchenhofer says. “But solely relying on one instrument, especially when policymaking comes into play, is probably too incomplete a picture to inform science and also airlines regarding contrail avoidance. We really need to fill this gap with other sensors.”

The team says other sensors could include networks of cameras on the ground that under ideal conditions can spot contrails as planes form them in real time. These smaller, “younger” contrails are typically missed by geostationary satellites. Once scientists have this ground-based data, they can match the contrail to the plane and use the plane’s flight data to identify the exact altitude at which the contrail appears. They could then track the contrail as it grows and spreads through the atmosphere, using geostationary images. Eventually, with enough data, scientists could develop an accurate forecasting model, in real time, to predict whether a plane is heading toward a region where contrails might form and persist, and how it could change its altitude to avoid the region. 

“People see contrail avoidance as a near-term and cheap opportunity to attack one of the hardest-to-abate sectors in transportation,” Prashanth says. “We don’t have a lot of easy solutions in aviation to reduce our climate impact. But it is premature to do so until we have better tools to determine where in the atmosphere contrails will form, to understand their relative impacts and to verify avoidance outcomes.  We have to do this in a careful and rigorous manner, and this is where a lot of these pieces come in.”

This work was supported in part by the U.S. Federal Aviation Administration Office

of Environment and Energy. 

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Written by Jennifer Chu, MIT News

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Journal

Geophysical Research Letters

DOI

10.1029/2025GL118386 

Article Title

“Contrail observation limitations using geostationary satellites”

Contrails are a major driver of aviation’s climate impact

Chalmers University of Technology

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image: 

Aviation’s climate impact extends beyond carbon dioxide emissions. A new study from Chalmers University of Technology and the University of Gothenburg, Sweden, and Imperial College, UK, reveals that contrails can represent a significant portion of aviation’s overall climate cost. The study also shows that climate impact can be reduced by optimising flight routes.

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Credit: Wikimedia Commons, CC BY-SA 2.5 | André Karwath

Aviation’s climate impact extends beyond carbon dioxide emissions. A new study from Chalmers University of Technology and the University of Gothenburg, Sweden, and Imperial College, UK, reveals that contrails can represent a significant portion of aviation’s overall climate cost. The study also shows that climate impact can be reduced by optimising flight routes.

In a new article in Nature Communications, The social costs of aviation CO₂ and contrail cirrus, the researchers demonstrate that both CO₂ emissions and contrail formation contribute materially to aviation’s climate impact – and that the associated societal costs differ substantially depending on weather patterns and routing decisions. They find that, at the global level, contrails account for about 15 percent of aviation’s climate impact when measured in economic terms.

After also analysing nearly half a million flights across the North Atlantic, the research team has generated new insights that can support both industry and policymakers in guiding aviation towards more climate optimal operations. Drawing on extensive flight and meteorological data, in combination with a contrail model and an advanced climate-economy model, the researchers estimated the climate and societal cost attributable to each emission source.

“Our research provides a basis for strategies to reduce the climate impact of contrails. Our calculations can be used for optimisation of flight routes where climate impact is considered alongside, for example, fuel cost and travel time. The results give airline operators and air traffic management new tools for climate optimisation. This could bring significant climate and societal benefits,” says Susanne Pettersson, postdoctoral researcher at the Department of Space, Earth and Environment at Chalmers.

The study shows that 38 percent of flights generate contrails that have a warming effect. It also shows that it would be beneficial from a climate perspective to reduce the formation of contrails of almost all these flights through minor rerouting, to avoid contrail formation, even if this results in slightly higher carbon dioxide emissions.

“The new knowledge also provides a foundation for designing new regulations and policy instruments to reduce aviation’s climate impact. The European Commission is currently working on proposals to steer aviation towards lower climate impact, and our new study can hopefully support this process,” says Daniel Johansson, associate professor at the Department of Space, Earth and Environment at Chalmers and one of the lead authors of the next IPCC climate report.

Learn more on contrails, aviation and climate change: Read an article written by the researchers as a Resources For the Future (RFF) issue in brief.

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Journal

Nature Communications

DOI

10.1038/s41467-025-64355-5 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

The social costs of aviation CO₂ and contrail cirrus

Advanced flight emissions calculator built by Surrey shows the real cost of flying

Many carbon calculators used by airlines and travel companies are dramatically underestimating the real climate damage caused by air travel, according to new research from the University of Surrey

University of Surrey

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The team, which includes Professor Xavier Font from the Centre for Sustainability and Wellbeing in the Visitor Economy, and Professor Jhuma Sadhukhan, Dr Jonathan Chenoweth and Finn McFall from the Centre for Environment and Sustainability, have developed a tool that shows the true footprint of a flight can be more than double current industry estimates – especially for premium passengers. 

The Air Travel Passenger Dynamic Emissions Calculator (ATP-DEC) is the first to account for the full life cycle of flying. It includes not only CO2 but also other warming effects such as nitrogen oxides, water vapour and contrail-induced cloudiness, which most calculators ignore. These “non-Kyoto” impacts can be more than twice the size of the CO2 emissions from a flight. 

The study, published in Nature Communications Earth and Environment, also factors in upstream emissions from fuel production and in-flight services, as well as the environmental cost of airports and aircraft over their lifetimes. It adjusts for real-world flight paths using historical flight path data, capturing the extra fuel burn from diversions, delays and airspace closures – something static calculators cannot do. 

Finn McFall, Knowledge Transfer Partnership Associate at the University of Surrey and co-author of the study, said:

“We have proved that existing flight data can capture real world variations. By delivering a transparent, source-by-source breakdown of emissions per flight, travellers and policymakers can make smarter, targeted climate decisions.” 

Adding to this, Eduard Goean, Visiting Professor at the University of Surrey and VP of Therme Group, a funding body for this research project, said: 

“By combining life-cycle analysis with real-world flight data, ATP-DEC will provide regulators, airlines and passengers with far more accurate and transparent information on carbon disclosure, helping align aviation industry with climate targets and the newest regulations in EU” 

Xavier Font, co-author of the study and Professor of Sustainability Marketing at the University of Surrey, said:

“The aviation sector has a responsibility to be honest about the environmental cost of flying. Without accurate data, we cannot design effective taxes, offsets or behaviour changes. Our tool puts robust, transparent science into the hands of those who can drive real change.” 

Benchmark tests against over 30,000 flights show ATP-DEC’s estimates closely match actual post-flight data, compared with substantial under-reporting by leading calculators. On some long-haul routes, standard methods understated per-passenger emissions by tens of thousands of tonnes in a single year. For example, the closure of Russian airspace means that many long-haul flights between Europe and Asia take detours of thousands of kilometres, consuming more fuel, and producing more emissions. The ATP-DEC captures this operational variation, while existing static calculators cannot. 

Professor Font continued: 

“Airlines, booking platforms and policymakers could integrate ATP-DEC into their systems immediately. Its modular design means it can evolve with new aircraft types, sustainable fuels and more advanced climate models. It also links directly to blockchain-verified carbon offsetting projects, making it easier to take credible action.  

“Industry-wide, this model could set a new benchmark for climate transparency, replacing outdated tools that mislead the public and delay action on aviation’s environmental impact.” 

[ENDS] 

Note to editors:

• Finn McFall and Professor Xavier Font are available for interview, please contact mediarelations@surrey.ac.uk to arrange.   

• The full paper is available in Nature Communications Earth and Environment

• Explanation of details within the ATP-DEC:  

1. Well-To-Tank (WTT) – The CO2e from producing, transporting, and loading the aviation fuel before its used. Adjusted to exclude emissions related to the mass of freight and passenger luggage onboard. 
2. Tank-To-Wake (TTW) – The CO2e released when the fuel is burned during the flight itself (take-off, cruising and landing). Adjusted to exclude emissions related to the mass of freight and passenger luggage onboard. 
3. Carry-on luggage – The TTW and WTT emissions from the passenger hand baggage. 
4. Checked luggage – The TTW and WTT emissions from the passenger hold baggage. 
5. In-flight services – The footprint of catering, onboard waste and other passenger services. 
6. Airport – The share of emissions from airport construction, operation, and disposal, spread over its lifetime, per passenger. 
7. Aircraft – The share of emissions from manufacture, maintenance, and disposal of the aircraft, spread over its lifetime, per passenger. 
8. Nitrogen oxides (NOx) – Gases released at high altitude that contribute to ozone formation and warming. 
9. Water vapour (H₂O) – Steam emitted by aircraft engines at altitude that can trap heat in the atmosphere. 
10. Contrail-induced cloudiness (CiC) – The thin ice-crystal clouds formed by engine exhaust in certain conditions, which can trap heat and significantly amplify warming. 

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Journal

Communications Earth & Environment

DOI

10.1038/s43247-025-02847-4 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Aviation passenger carbon footprint calculator with comprehensive emissions, life cycle coverage, and historical adjustment

Article Publication Date

29-Oct-2025