What Are Contrails (Condensation Trails)?
The wispy white lines that we observe in the sky produced by aircraft are called "contrails." When the hot and humid exhaust produced by a jet engine meets the cold air, the water vapor rapidly condenses and forms ice crystals. This reaction creates thin, long, artificial clouds. These trails may be visible for only a few minutes, or may persist for hours, eventually resembling wispy cirrus clouds.
In 2023, the aviation industry accounted for 2.5% of global energy-related CO2 emissions. In addition, it has grown faster between 2000 and 2019 than rail, road or shipping. The aviation industry has committed to reaching net zero by 2050, but eliminating the carbon emissions from jet fuel may not be enough to stop the climate impacts of air travel and transport.
Only about one-third of the total warming effect of the aviation industry on the climate is due to CO₂. The remaining major impact comes from the contrails produced by aircraft and the cirrus clouds that these trails spread and form. While these artificial clouds reflect some of the sunlight, they also trap outgoing heat in the atmosphere. Therefore, they cause a strong warming effect.
In brief, about two-thirds of aviation's total warming effect comes from contrails and the resulting cirrus-resembling clouds, not from carbon dioxide.
Let's dive into the details.
Contrails form as a result of hot and moist exhaust from a jet engine and the freezing air in the upper atmosphere. Water vapor rapidly turns into ice crystals, forming thin, long clouds. Contrails may sometimes dissipate within minutes, or they may persist in the air, growing into wispy clouds resembling cirrus clouds.
Scientific research reveal that persistent contrails, in particular, have a significant warming effect on the climate. These wispy clouds trap some of the heat radiating out from the Earth's surface and can persist in the atmosphere throughout the night.
The impact of contrails on the climate is much more significant than most people think. Because these trails are not just composed of water vapor. Contrails form when water vapor and particles from aircraft exhaust condense into ice crystals in the upper atmosphere. As they persist in the atmosphere, they extend and form a wispy cloud layer. This layer acts similar to natural cirrus clouds formed at high altitudes. Although the layer reflects some of the sunlight back into space during the day, it traps heat radiating out from the Earth's surface in the atmosphere during the night.
Therefore, scientists categorize contrails as a "short-lived but strong warming effect." However, this effect can dramatically increase depending on the flight altitude, the humidity in the air, and the temperature.
Scientific research reveal that the impact of contrails can be lessened under specific conditions and with careful planning. The reason is that contrails only form under certain humidity and temperature conditions. The impact of the flights can be reduced by changing the altitude of a small number of flights to avoid layers where contrails are likely to form under specific meteorological conditions.
Research conducted in 2020 in Imperial College London revealed that just 2% of commercial flights were responsible for 80% of contrail-induced climate impact. It is estimated that the warming effect can be cut by half with minor changes in the altitudes of these flights. The strategy to be adopted by airlines is considered as one of the rare solutions that provides a high but cost-efficient impact.
Simply: Planes flying either a few hundred feet higher or lower than their actual flight paths may cut by half of the contrail formation.
The scientific community has recognized that the impacts of contrails can be mitigated, yet this knowledge has garnered only minimal public interest. There are numerous reasons for this. Airlines have prioritized emission reduction for many years, but most climate plans have overlooked impacts other than CO₂. Yet, data indicates that a considerable part of the warming effect is attributed to contrails.
Operational challenges are also another significant issue to consider. Alterations in altitude demand increased coordination concerning air traffic oversight, fuel planning, and route optimization. Nevertheless, the analysis indicates that the majority of these modifications can be applied to flights with minimal expense. Regardless, this strategy has yet to be made compulsory within the industry. Although strategies to mitigate the impacts of contrails are promising, the operational challenges and extra carbon emissions resulting from altitude adjustments complicate the direct implementation of these solutions to all flights.
Recent years have witnessed encouraging technological advancements that hold promise for decreasing the climate effects of aviation. The most notable of these advancements is “Project Contrails.” Project Contrails is a research program run jointly by Google, American Airlines, and Breakthrough Energy, using mainly AI models. The project develops AI models that integrate satellite imagery, flight path data, and intricate weather models to anticipate the conditions under which contrails are likely to appear. These models forecast the altitudes at which contrails will form for a specific flight. Then, flight planning systems optimize the aircraft's route or altitude by making minor adjustments of a few hundred feet up or down to avoid forming these trails. This indicates that airlines have the potential to greatly lessen their climate impact without the need for substantial infrastructure investments, but merely by employing smarter data and AI-driven route optimization.
Despite the fact that contrails have been extensively researched in scientific literature, public interest has remained restricted and fragmented. Thus, the initial action is to foster a more comprehensive understanding of the issue, including its scientific basis and existing implementation constraints. The climate impact of contrails should be regarded as a complementary issue to be assessed alongside the carbon emissions generated by aviation.
It is crucial to assess the approaches to mitigating contrails alongside cleaner fuels and long-term technological transformations. In this context, enhanced understanding can facilitate the development of more balanced policies and more informed decision-making processes. Even insignificant enhancements, when implemented under suitable circumstances and within the appropriate context, can significantly reduce the overall climate impact of aviation.
The white trails that vanish behind aircraft are a much more significant part of the climate story than we comprehend. Moreover, the solution does not require an innovative engine technology or major investments. Even the use of smarter data, Ai-driven forecasts, and small altitude adjustments can significantly lessen the warming effect of the aviation industry. Therefore, the aviation of the future will be shaped by more informed and data-driven decisions, alongside structural solutions such as cleaner fuels. A scientific understanding of the impact of contrails makes it possible to holistically assess the overall climate impact of the aviation industry. As knowledge expands, the processes involved in decision-making become more robust, and even minor enhancements can lead to significant contributions towards a more resilient and sustainable future.