At high cruising altitudes where temperatures drop sharply, aircraft emit condensation trails made of water vapor that stretch into long white lines across the sky. These contrails, though seemingly harmless, come in many forms and can influence the atmosphere and climate in measurable ways.
A growing consensus among airlines and scientists is that these trails contribute to climate warming. In some cases, their formation leads to cloudiness at flight levels that traps heat, altering local radiative balance in the upper atmosphere.
Recent research from Europe suggests that contrails may play a significant role in global warming, potentially rivaling or exceeding the impact of some fuel-emission components. This field of study, focused on effective radiative forcing, assesses the total warming influence rather than isolating CO2 alone.
North American carriers, including Fort Worth-based American Airlines and Dallas-based Southwest Airlines, are exploring which contrail patterns pose the greatest environmental risk and evaluating strategies to reduce harm where feasible.
Andrew Chen, an aviation expert with the climate-focused Rocky Mountain Institute, notes that aviation’s warming impact may be larger than previously estimated.
Alongside American and Southwest, a coalition includes other major airlines and manufacturers such as Boeing, Airbus, United Airlines, Alaska Airlines, Virgin Atlantic, Google Research, and a broader group of industry stakeholders. This collaboration intensified after Delta Airlines announced a partnership with the Massachusetts Institute of Technology to study contrail formation and mitigation methods.
The airline sector has set ambitious environmental targets in recent years, but much of the technology needed for full achievement remains under development. Both American and Southwest have signaled 2050 as a target year to substantially reduce their emissions footprint. Emission reductions to date have largely come from more fuel-efficient engines, while researchers explore sustainable fuels produced from recycled oils, hydrogen options, and potential electric propulsion when feasible.
Its effects are increasingly known
Contrail trails present a distinct challenge beyond traditional carbon emissions strategies.
Jill Blickstein, vice president of sustainability at American Airlines, explains that understanding the net effect of contrails has evolved. Morning contrails can produce cooling effects while those formed at night tend to trap heat more effectively. The overall balance of warming versus cooling is a topic of ongoing analysis, with clearer signals emerging in recent years.
Delta Air Lines reports that roughly 65% of cruising-altitude flights between 30,000 and 45,000 feet generate contrail formations, though most dissipate quickly and have limited warming impact. Approximately 10% form more persistent patterns that can endure for hours.
The most adverse effects are often observed at night when the earth is cooling naturally, and man-made clouds at high altitudes can hinder heat loss from the planet.
Small numbers of flights occur at night, but those are the ones that contribute most to contrail formation. Daytime trails also matter, as they can divert sunlight away from the surface even if some cloud cover reduces solar flux.
Airlines know how to reduce contrails
Helen Giles, director of environmental sustainability at Southwest Airlines, notes that flight crews and airlines can avoid contrail formation, but doing so requires careful planning that weighs weather, turbulence, and speed. In some cases, avoiding contrails means using routes or altitudes that consume more fuel than usual.
Forecasting the exact conditions that produce contrails within six to eight miles is as challenging as forecasting ground weather. Even a best guess has limits given high aircraft speeds. The objective is to advance predictive capabilities to understand where contrails are likely to form and how long they persist.
The plan involves satellite imagery and sensor data to determine when planes begin producing contrails and how long they linger. This data, combined with weather, turbulence, speed, and other factors, will help identify the conditions that yield the most contrail formation and support informed flight planning decisions.
From an operational perspective, experts believe measurable reduction is possible, but a formal plan awaits a validated model that weighs radiative forcing against fuel emissions and overall climate impact.
There is hope that small shifts in flight altitude and routing can prevent contrail formation in the most intense conditions, while not compromising safety or efficiency.
Southwest has formed a team combining environmental experts with pilots and network planners to study this issue, with eventual collaboration anticipated with regulatory bodies and aviation authorities.
According to Blickstein of American, modest flight adjustments could suppress contrails, but a comprehensive model will be essential to guide pilots and crews with simple, actionable information. The journey to reduce contrails is just beginning, and ongoing learning will shape the path forward.
In any case, the race to reduce contrails and their previously underappreciated climate effects appears to be underway.
Reference article: citation: phys.org, 2022.
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