MIT warns: without more satellites we don't see the real climate impact of aircraft contrails

MIT: More eyes in the sky reveal how much aircraft contrails warm the planet

A new paper from researchers at the Massachusetts Institute of Technology (MIT) opens an important chapter in the debate over the climate impact of air travel. By analyzing satellite imagery, scientists have shown that geostationary orbit satellites, which we rely on most today, miss about 80 percent of the condensation trails (contrails) that are visible from more precise satellites in low Earth orbit. The conclusion is clear: without "more eyes in the sky," it is difficult to accurately estimate how much aviation truly warms the atmosphere – and how we can quickly reduce that effect.

Contrails form when hot jet engine exhaust meets cold and humid layers of air. The ice crystals that then form create thin white streaks behind the aircraft, and in suitable atmospheric conditions, these streaks can turn into wide, long-lasting clouds that cover large areas of the sky for hours. Although they seem harmless at first glance, recent scientific analyses show that contrails could be responsible for approximately half of aviation's total climate impact, comparable to the impact of CO₂ emissions from the same sector.

At a time when Europe and the rest of the world are increasing pressure to decarbonize air transport, the MIT study comes as both a warning and an opportunity: if we want to seriously apply strategies to avoid the most climate-damaging trails, we must first know how many there are, where they form, and how long they last. And for that, it turns out, we can no longer rely on just one type of satellite.

Contrails as hidden aviation emissions

The climate impact of aviation has long been identified almost exclusively with carbon dioxide emissions. However, over the past decade, a growing scientific consensus has emerged that non-CO₂ effects – primarily contrails and the clouds formed by their evolution – can have an equally large, and in a shorter time horizon even greater, contribution to global warming than CO₂ itself. Analyses by international air transport organizations estimate that the radiative effect of contrails is comparable in magnitude to the effects of CO₂ emissions from aviation.

The key problem is that not all contrails are equal. Many dissipate within minutes and have a limited or even slightly cooling effect because they reflect part of the Sun's energy back into space. Others, especially those formed in night and winter conditions, can persist for hours and act like a thermal blanket that traps long-wave radiation from the planet's surface. Scientific papers indicate that a relatively small number of flights – only a few percent – generate the majority of the total warming effect of contrails, while most trails have a much smaller climate impact.

Therefore, contrail avoidance is increasingly mentioned as a "quick win" in aviation climate policy. Estimates show that optimized rerouting of a very small number of flights through a few hundred meters of different flight altitude could halve the climate warming caused by contrails, with only a marginal increase in fuel consumption and cost per ticket. But for such measures to be effective, it is necessary to reliably identify areas of the atmosphere where persistent, most climate-damaging trails will form at all. This is where satellites come into play.

Why satellites are key to "contrail forecasting"

Most previous research on contrails has relied on geostationary satellite imagery. These satellites "sit" over the same point on Earth at an altitude of about 36,000 kilometers and continuously record a large area, with a new frame every few minutes. In practice, this means that meteorological services, aviation authorities, and researchers get a continuous picture of the development of clouds, storms, and high ice clouds, which include developed contrails.

However, such spatial and temporal coverage comes at a cost – limited resolution. Given the distance of geostationary satellites, individual pixels in an image can represent several kilometers on the ground. This is enough to clearly see large, spread-out trails and cloud structures, but not the earliest stages of contrail formation, when the trails are still short and thin, right at the moment they exit the aircraft jet engines.

On the other hand, satellites in low Earth orbit (LEO) – such as those equipped with the VIIRS instrument – orbit at altitudes of several hundred kilometers and fly over the Earth in narrow strips. Their images have a significantly finer spatial resolution and can discern much thinner and shorter structures in the atmosphere. However, LEO satellites fly over the same part of the Earth only once or a few times a day, which means they do not provide continuous monitoring of the development of clouds and contrails from minute to minute.

In practice, geostationary satellites have established themselves as the "workhorses" of contrail detection systems. Numerous research projects are based on them, as well as experimental algorithms that attempt to predict in real-time where persistent contrails will appear. MIT researchers decided to test how complete this picture is – and what we are missing when we only take geostationary images into account.

What the MIT comparison of GEO and LEO images showed

In a new paper published in the journal Geophysical Research Letters, a team from MIT's Department of Aeronautics and Astronautics compared two main types of satellite contrail observations. As a representative of the geostationary platform, they took the Advanced Baseline Imager (ABI) instrument on one of the US meteorological satellites, while they used the Visible Infrared Radiometer Suite (VIIRS) instrument from several low-orbit satellites as a high-resolution reference.

For each month from December 2023 to November 2024, the researchers selected one VIIRS image of the continental United States. They then found the closest possible matching images of the same area from the geostationary ABI. All images were in the infrared spectrum and displayed in false colors to more easily highlight thin ice structures corresponding to contrails, both day and night.

Meticulous manual work followed: for each image, scientists manually searched the frame, zoomed into individual parts, and marked every clearly visible contrail. They then compared how many of these trails were recognizable on geostationary images and how many were visible only on high-resolution LEO images.

The result was surprisingly unambiguous. On average, about 80 percent of the trails clearly distinguishable on LEO images were not seen on geostationary satellite images. GEO instruments are much better at "catching" long, wide, and developed contrails, while VIIRS and similar LEO sensors also reveal a whole spectrum of shorter, thinner, and "younger" trails that have just exited aircraft engines or have only just begun to spread.

The authors emphasize that this does not mean that 80 percent of the climate impact of contrails is invisible from Earth orbit. The large, long-lasting trails that geostationary satellites do record are likely responsible for the largest part of total warming because they stay in the atmosphere longer and cover larger areas. But at the same time, the fact that the vast majority of trails are not seen at all in standard geostationary products means that models relying only on GEO data necessarily give an incomplete picture.

The MIT team therefore concludes that, especially in the context of future public policies and potential contrail avoidance obligations for airlines, we should not rely on a single instrument or a single orbital configuration. Only by combining data from geostationary and low-orbit satellites, supplemented by ground observations, is it possible to obtain credible statistics on where, when, and how often climate-relevant contrails form.

From laboratories to flight control: can contrails be avoided in practice?

The idea that pilots, with the help of new weather forecasts and satellite analyses, could adjust flight altitude to avoid zones suitable for the formation of persistent contrails is no longer pure theory. Over recent years, numerous experimental flights have been conducted in Europe and North America in which airlines, research institutes, and air traffic control tested operational "detours" to reduce the formation of the most harmful trails.

Studies show that a small number of targeted route changes – often on only a few percent of all flights – can result in a significant reduction in the climate impact of contrails. Some research suggests that about 3 percent of global flights create approximately 80 percent of the total warming associated with contrails. If the atmospheric layers in which persistent, optically thick trails will form are identified in advance for these flights and the flights are rerouted by a few hundred meters above or below those layers, it is possible to remove more than half of that effect with a global fuel consumption increase of less than one percent.

The European Union Aviation Safety Agency and research centers such as EUROCONTROL's Maastricht Upper Area Control Centre (MUAC) are already testing how to integrate such solutions into the daily work of controllers and flight planners. Key challenges are forecast reliability, airspace workload, and real-time data availability. This is where the MIT analysis fits in as an important reminder that the quality of contrail avoidance forecasting cannot be evaluated without a detailed understanding of the limitations of the satellite sensors themselves.

For now, pilot projects mainly combine meteorological models, historical satellite imagery, and in-flight verification, and results are retroactively compared with satellite observations to see if a particular flight actually produced fewer persistent trails. If part of these trails remains invisible to geostationary satellites, there is a risk that the effectiveness of measures will be overestimated or underestimated, depending on which part of the statistics is ignored.

Europe announces monitoring of non-CO₂ air traffic effects

Meanwhile, the political framework in Europe is changing rapidly. As of 2025, the European Union has begun introducing the obligation to monitor and report on non-CO₂ effects of air traffic, including contrails, for flights within the Union. The plan is to extend such monitoring to international flights in the second half of the decade. The goal is that when assessing the climate footprint of air carriers, not only carbon dioxide emissions are taken into account, but also short-term but intense effects like contrails.

Parallel to European initiatives, a discussion is being held at the level of the International Civil Aviation Organization (ICAO) on how to better incorporate non-CO₂ effects into the existing system of market mechanisms and standards, such as the global CORSIA scheme. Although there is no globally binding framework for contrails for now, pressure from the scientific community and civil society to include this aspect in national climate plans is growing stronger, especially after new studies showing that contrails are one of the main drivers of the total climate cost of aviation.

The MIT research fits into this trend as a very concrete contribution – it shows that even the "picture of the sky" on which we build policies is still incomplete. If in the future, for example, additional fees are introduced for flights entering zones of high probability of persistent contrail formation, it will be extremely important for regulators to know how accurate the detection systems they use are.

More sensors, open data, and room for artificial intelligence

The authors of the MIT study therefore advocate an approach that combines geostationary and LEO satellites with ground-based camera networks. Under ideal conditions, ground cameras distributed around major air corridors can detect the moment of contrail formation in real-time and link it to a specific flight and its altitude. The same trail can then be tracked in the following hours with the help of geostationary satellites to reconstruct its "life cycle" – from a thin jet behind the engine to a spread-out cloud of ice crystals.

Such an approach opens the way to the development of significantly more precise models that could forecast where persistent, most climate-relevant trails will be created in the coming hours. Behind this is a huge amount of data: already today there are publicly available sets of manually identified contrails on satellite images, intended precisely for training machine learning algorithms. When these datasets are linked with detailed information on flights and atmospheric conditions, it is possible to develop models that warn flight planners and air traffic control in real-time of zones of increased risk.

The role of geostationary satellites does not disappear – on the contrary, they remain a key source of continuous observations that cannot be replaced. However, as MIT results show, their limitations must be clearly taken into account: without supplementary data from low-orbit satellites and from the ground, the calculation of the climate impact of air traffic risks being systematically underestimated or incorrectly distributed among flights and regions.

For the aviation industry, which is already facing high costs of decarbonization through sustainable fuels and future low-carbon technologies, contrails represent perhaps the closest opportunity for a relatively cheap reduction of the climate footprint. But the MIT team warns that it would be premature to introduce broad operational contrail avoidance obligations without a firm scientific basis and reliable monitoring tools. As the authors emphasize, only by combining different sensors, precise meteorological forecasts, and systematic outcome verification is it possible to develop strategies that will truly reduce warming, and not just move the problem from one part of the sky to another.

In the long run, the success of such approaches will depend not only on progress in satellite technology but also on the political will to truly introduce new tools into operational practice. While the number of flights continues to grow and climate goals become stricter, the question of contrails is slowly moving from scientific papers to the center of the debate on the future of air travel. Whether "more eyes in the sky" will also become more real climate responsibility is now primarily a question of choice for regulators, industry, and passengers.

Sources:
- Massachusetts Institute of Technology / Mirage News – press release on research into limitations of geostationary satellites in contrail detection (link)
- Euchenhofer M. V. et al. – scientific and technical materials on contrail observation and geostationary satellite limitations, including publicly available sets of manually identified trails (link)
- Air Transport Action Group (ATAG) – overview document on the climate impact of contrails and operational options for their reduction (link)
- Transport & Environment – analysis of costs and potential for contrail avoidance through limited flight path changes (link)
- EUROCONTROL / MUAC – article on the development and testing of contrail avoidance measures in European airspace (link)
- Chalmers University of Technology – research on the total climate cost of aviation and the role of contrails (link)
- Financial Times – analysis of the climate impact of air traffic and the role of contrails, including European plans for monitoring non-CO₂ flight effects (link)