Southwest Airlines is excited to share we are joining forces with academic, technology, and nonprofit partners to launch the Contrail Impact Task Force. The cross-sectoral task force was established to explore the formation and mitigation of persistent condensation trails, or “contrails,” that might affect the climate impact of some flights.
At Southwest, we take pride in being the airline with Heart, and that includes respecting our Planet. We recognize addressing the potential impact of contrails is an important step in our industry’s environmental sustainability journey, and we are eager to better understand how each airline’s potential impact may vary based on its routes and schedule.
Last month, we even hosted the task force’s first workshop at our headquarters in Dallas. Through this cross-functional collaboration, we hope to play a pivotal part in advancing science! To learn more about the Contrail Impact Task Force, keep reading to hear from two of its members:
The following was authored by Joey Cathcart and Andrew Chen from the Contrail Impact Task Force
Today, we do not know the precise warming magnitude of aviation-induced cloudiness, but we see a growing scientific consensus that the impact on climate may be comparable to aviation CO 2 emissions. Building off alliances and partnerships to decarbonize aviation, RMI is bringing together the aviation industry—including Southwest Airlines, the tech sector, and academic leaders to explore opportunities to address the warming impact of certain contrails.
Aviation stakeholders recognize the importance of determining the precise impact of aviation-induced cloudiness and exploring possible solutions. While potential solutions have been largely unavailable to the industry, new prediction and verification tools to help mitigate warming from aviation-induced cloudiness are in development today. There may be no silver bullet solution, but through collaboration, tool developers and aviation stakeholders can work to better understand the science of contrails, explore potential tools to avoid their formation, and identify possible mitigation opportunities to reduce their impact.
What Are Contrails?
When you look up into the sky, on some days you may notice white, linear trails behind some aircraft. These are known as condensation trails, commonly referred to as contrails.
Aircraft can produce contrails at cruise altitudes—typically between 32,000 and 42,000 feet above the Earth in the upper troposphere—in regions of the atmosphere where the humidity is high enough and the temperature is cold enough for water to condense. Under these conditions, small particles such as soot exhausted by aircraft engines serve as condensation nuclei suitable for water droplet formation. As the particles cool and mix with the surrounding atmosphere, the water droplets freeze into ice crystals, creating contrails.
The Climate Impact of Contrails
The aviation industry contributes approximately 2.4 percent of global CO 2 emissions; however, non-CO 2 factors—including contrails—also contribute to atmospheric warming, though their exact impact remains uncertain. Depending on the atmospheric conditions, contrails can either dissipate or become persistent and evolve into contrail-cirrus clouds. These formations can last for hours. During daytime hours, persistent contrail-cirrus clouds help reflect some incoming solar radiation, potentially resulting in slight cooling. However, if persistent contrails form during or extend into nighttime hours, they can trap outgoing thermal radiation from the Earth’s surface, resulting in potentially significant warming.
Not all aircraft produce contrails. Studies to date have found that less than 10 percent of flights may be responsible for 80 percent of contrail warming. Through focused, collaborative effort, the aviation industry can better understand the impact of contrails and explore potential solutions.
Collaboration For Contrail Mitigation
In response to this area of interest, RMI and Breakthrough Energy have assembled the Contrail Impact Task Force. The task force aims to reduce the climate impact from aviation contrails by:
Sharing and expanding on the latest science on the climate impact of contrails
Developing actionable strategies to avoid warming contrails
Analyzing the operational and financial challenges of implementing potential solutions
Establishing a roadmap for implementation and validation of contrail mitigation tools
By collaborating with each other, participants in the Contrail Impact Task Force can work to integrate identified contrail risk areas into flight plans, just like turbulence, icing, or inclement weather are incorporated into flight planning today.
Determining what it will take to integrate contrail prediction tools into existing flight planning platforms — and verifying contrail formation or avoidance — is only part of the challenge. For potential contrail mitigation solutions to be viable at scale, their impact on existing factors needs to be well understood. First and foremost, solutions must maintain the highest level of safety that exists in aviation today. Airspace is a limited resource, and ensuring appropriate separation between aircraft is critical. With vertical and lateral route adjustments being the primary means of contrail mitigation, potential solutions will need to be evaluated to determine their compatibility with existing procedures and ensure their application does not constrain airspace or impact safety.
In addition to safety and airspace considerations, another factor to evaluate is the potential impact on flight planning, pilot, and air traffic management workload. For example, to accommodate an aircraft seeking to avoid contrail formation, air traffic management may need to reroute another aircraft as well. Finally, both vertical and lateral route adjustments to avoid contrail formation will also affect fuel consumption, creating a trade-off between direct and indirect climate impacts. This relationship and potential trade-offs between CO 2 and non-CO 2 emissions will need to be well understood to ensure that flights applying prospective contrail mitigation solutions achieve the best climate outcome possible.
The creation of the Contrail Impact Task Force is a significant step in fostering the industry's climate action. As a cross-industry stakeholder group, it demonstrates leadership and continued commitment to reducing aviation’s climate impact. The exact contribution of contrails to climate warming may still be uncertain, but a collaborative approach can serve as a catalyst for developing a greater understanding of contrail science, prediction and verification tools, and mitigation opportunities.
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