Contrail Opportunity Index

Already dealing with huge challenges, airlines face a mammoth task to achieve their net zero targets and are in urgent need of solutions. The current discourse mostly focuses on reducing in-flight CO2 emissions through Sustainable Aviation Fuels, alongside emerging electric and hydrogen technologies, but these solutions may take decades to scale effectively.

Reducing contrails, which account for a significant proportion of the sector’s total radiative forcing impact, offers a far more immediate upside opportunity. In this paper we draw on fresh research to quantify and understand that opportunity in the context of ongoing industry initiatives.

Contrails: the challenge and the opportunity

The mechanism by which contrails can exacerbate global warming has been understood since the 1990s, when NASA’s Patrick Minnis first highlighted their radiative forcing effects. Under certain atmospheric conditions, they persist as cirrus clouds, which cause cooling when they reflect incoming sunlight back into space, and warming when they trap heat radiating from the earth’s surface.

While the cooling effect of contrails is thus limited to daylight hours, their warming effect persists around the clock. Consequently, without proper management, their net impact is to contribute to temperature rises.

Recent scientific advancements have deepened our understanding of this impact, though estimates of its size remain variable. Crucially, individual flights experience varying degrees of contrail impact according to different operational characteristics, such as:

• Geographic location: different regions exhibit distinct weather patterns, influencing contrail formation.
• Aircraft and engine specs: different types of aircraft and engines in use affect flight altitudes and emit varying levels of soot, a key factor in ice nucleation and contrail formation.
• Flight timing: flights departing in the afternoon tend to contribute to a higher contrail impact, as the contrails formed during this period often persist into the night.
• Weather: humidity, temperature, and atmospheric pressure all impact contrail formation, with contrails more likely to form in colder temperatures and higher humidity.

Most contrail impact is generated by flights to and from Europe and North America, where larger volumes of commercial air traffic frequently intersect with conducive atmospheric conditions for contrail formation. Other regions with high traffic, such as Asia Pacific, observe lower contrail impact, largely because of less contrail-prone cruise altitudes, as well as weather phenomena such as the Hadley Circulation. 

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The size of the prize
 

These figures are highly relevant in the context of the EU’s imminent plans to introduce a new Monitoring, Reporting, and Verification (MRV) scheme for aviation’s non-CO2 environmental effects, including contrails. By the end of 2027, based on the results from the application of the MRV framework for non-CO2 aviation effects, the EU will work on a legislative proposal to mitigate non-CO2 aviation effects by expanding the scope of the EU ETS to include non-CO2 aviation effects.

Today, opinions differ on whether the monitoring scheme should encompass all flights that depart from or arrive in EU member states, or remain limited to intra-EU flights only, to already align with the scope of the EU Emissions Trading Scheme (ETS). In either case, the contrails impact remains large. 

By isolating the contrail impact of each individual flight, we can now, for the first time, assess the implications of choosing one reporting scope over another. On an airline-by-airline basis, we also observe significant variability in contrail impact depending on the reporting scope, primarily driven by the airline's route network.

Whilst the scheme’s aim is currently to encompass all flights that depart from or arrive in EU member states, some airlines are advocating to reduce its scope to intra-EU flights only, to align with the scope of the EU Emissions Trading Scheme (ETS). In either case, the contrails impact remains large.

Crucially, however, this impact is very unevenly distributed. In fact, according to Estuaire’s analysis, in 2023 just 2.9% of flights generated 80% of the total radiative forcing effect of contrails.

This insight represents a huge opportunity: for most airlines, substantial climate savings can be realised with minimal fuel penalties by rerouting only a small number of flights. Estuaire’s analysis makes this clearer at the airline level, where those airlines with the highest concentrations of contrail impact can be ranked accordingly.

In the following table, we have redacted this initial ranking, but for sector transparency seek to open this up in collaboration with airlines over time.