Persistent contrails and aviation-induced cloudiness could be as significant as carbon dioxide emissions in aviation’s contribution to global warming, according to a report from the National Academies of Sciences, Engineering, and Medicine. Commissioned by NASA and released today, the 100-page document proposes a federally coordinated research agenda to better understand and reduce the climate impact of contrails through scientific, operational, and policy pathways.
A multidisciplinary committee produced the report. The group included atmospheric scientists, engineers, government researchers, and industry representatives. Members were drawn from institutions such as MIT, the University of Michigan, Los Alamos National Laboratory, NASA Langley Research Center, and Pacific Northwest National Laboratory, with additional input from commercial aviation stakeholders, propulsion experts, and regulatory officials.
The premise of the report is that aviation’s contribution to global warming extends beyond CO2 emissions and there is a need to measure these possible impacts. While CO2 from fossil jet fuel accounts for roughly 2.5% of all carbon emissions, the report emphasizes that non-CO2 impacts—especially those from persistent contrails—could be of the same order of magnitude. As air traffic grows, these effects are expected to increase unless mitigation strategies are developed and implemented.
Contrails are defined in the document as line-shaped clouds that form when the exhaust from aircraft engines mixes with cold, humid air at cruising altitudes. As the exhaust cools, it becomes supersaturated with respect to liquid water, leading to the formation of droplets that rapidly freeze into ice crystals.
“When the surrounding atmosphere is supersaturated with respect to ice,” the report asserts, “these initial contrails can grow and persist into contrail cirrus clouds for hours…Persistent contrail cirrus, like naturally occurring cirrus clouds, will both scatter incoming sunlight back to space (cooling) and trap Earth’s outgoing thermal radiation (warming).”
This dual radiative effect may vary depending on the time of day and cloud characteristics. Daytime contrails may provide some cooling, while nighttime contrails could cause atmospheric warming. Modeling shows a net warming effect, particularly from persistent contrails that spread and merge into cirrus-like formations. Because these warming effects depend on specific atmospheric conditions, such as ice supersaturation, the report stresses the importance of forecasting systems that can identify where persistent contrails are likely to form.
The committee uses the term “aviation-induced cloudiness” to describe the broader climate-relevant effects of contrails and the cirrus clouds they generate. Throughout the report, contrails, persistent contrails, contrail cirrus, and aviation-induced cloudiness are used interchangeably. Importantly, only persistent contrail cirrus are considered climatically significant.
While contrails are a global issue according to the report, the U.S. is uniquely positioned to lead contrail research. NASA has conducted several studies of contrail formation, including a late 2024 test using a NASA DC-8 and a Boeing ecoDemonstrator 737-10 equipped for atmospheric sampling. However, the report also notes that the DC-8 was retired last year, and its replacement, the Boeing 777-200ER, is not expected to enter service until 2026.
NASA has also contributed satellite instruments and software. In addition, NOAA can provide weather modeling, and the FAA has the authority and infrastructure to integrate contrail forecasts into traffic management systems. The Department of Energy offers expertise in atmospheric modeling and high-performance computing.
Despite these assets, the report concludes that U.S. contrail research efforts remain fragmented across agencies and disconnected from operational planning, and it notes that geopolitical forces inhibit research in areas like China. It recommends that federal agencies establish a shared modeling infrastructure and a clear strategy, largely supported by NASA, to prioritize and coordinate research. This includes sharing resources that exist for contrail prediction and verification, advancing observational tools, and ensuring that scientific findings can be applied to flight trajectories for contrail avoidance.
Among the findings mentioned in the report is that the majority of contrail-related warming may come from a relatively small percentage of flights. This suggests that targeted mitigation, such as avoiding ice-supersaturated regions on specific high-impact routes, could offer climate benefits. The report notes recent studies that indicate these regions are often horizontally extensive but vertically shallow, typically spanning hundreds of kilometers in width but only a few hundred meters in depth.
The committee recommends new investments in measurement technologies, including sensors that can be installed on commercial aircraft to collect data on temperature, humidity, and ice supersaturation. This data could support the development of forecast models that can help dispatchers, pilots, and air traffic controllers minimize contrail formation while balancing fuel efficiency, safety, and traffic flow.
Specific recommendations in four key areas are outlined in the report: improving atmospheric measurements and observations; developing standardized modeling tools for contrail formation and evolution; building and validating operational forecasting systems; and coordinating these efforts through a national research strategy. These recommendations are aimed at enabling decision-makers, both in government and the private sector, to implement mitigations that are scientifically grounded and operationally feasible.
Also highlighted by the committee is the need for collaboration with the wider aviation industry. Aircraft manufacturers, propulsion system developers, and operators will play a role in evaluating and applying any potential mitigation strategies. These could include changes to routing, altitude selection, or fuel composition, particularly the adoption of sustainable aviation fuel (SAF), which has been shown to reduce contrail ice particle formation in some cases.
Throughout the report, the authors frame the issue of contrails not only as a technical and scientific challenge but also as a strategic one for the aviation sector. As regulatory discussions in Europe advance toward including non-CO2 effects in emissions reporting and climate policy frameworks, the U.S. will require its own data, tools, and readiness to respond. According to the report, “The United States needs sufficient data on the causes and effects of persistent contrails, and possible mitigating actions, to enable a response to this emerging regulatory environment.”
While the report does not prescribe specific policy measures, it lays the foundation for future regulatory and operational pathways. The authors acknowledge that contrail mitigation will not be a one-size-fits-all solution. Some interventions may be cost-effective only on certain routes or under specific atmospheric conditions. Still, the committee asserts that the potential climate benefits justify the investment in improved science, forecasting, and coordination.
With air traffic expected to continue growing in the coming decades, and international pressure mounting for measurable climate action, the development of a coordinated U.S. research agenda on contrails is seen as both a scientific imperative and an operational necessity. NASA’s ongoing involvement and recent collaborations with commercial partners indicate that initial steps are already underway—and the U.S. consortium is not the only group concerned with contrail research and mitigation.
In March, a new research initiative by Airbus and a consortium of 10 partners from four European countries was launched to study the climate and air quality effects of non-CO2 aircraft emissions, with a specific focus on contrails. The program—called Particle Emissions, Air Quality, and Climate Impact Related to Fuel Composition and Engine Cycle (PACIFIC)—will look into how different fuel blends, particularly SAF, influence contrail formation.
PACIFIC will use ground-based engine testing with an Airbus A350 and its Rolls-Royce engines to enable controlled assessments of combustion behavior. Tests will examine how soot forms during combustion and how this affects the quantity and composition of fine particles that can trigger contrail formation under varying engine power settings. According to Airbus’ Mark Bentall, the goal is to create a consistent testing framework linking lab-scale experiments at DLR with full-scale engine operations.
The PACIFIC consortium also aims to build better predictive tools and cost-benefit models to evaluate different fuel options and their potential regulatory implications. Bentall emphasized that although there is still uncertainty in the science of contrails, there is general agreement that they contribute to net atmospheric warming and should therefore be addressed in climate mitigation strategies.
Additionally, the article referenced NASA and GE Aerospace’s Contrail Optical Depth Experiment, launched in November 2024, which uses Lidar-equipped aircraft to study contrail structure in three dimensions.