How do airplane contrails impact Earth's climate?

Contrails, those wispy trails that jets leave behind as they move through the sky, are not as harmless as they might seem.

These long, thin clouds created in the wake of high-flying aircraft are surprisingly detrimental to the environment. Their formation involves a layered process, blending hot exhaust gases with the cold upper atmosphere.

Under certain conditions, these hazy shreds of condensed water vapor spread and transform into contrail cirrus clouds. Instead of dissipating into space, these clouds trap heat, contributing to over half of aviation’s total climate impact.

Climate impacts of contrails

Fangqun Yu, a senior researcher from the University at Albany‘s Atmospheric Sciences Research Center, has recently led a study focused on this troubling phenomenon.

The research took a closer look at the contrail formation process, scrutinizing the role of non-volatile (soot) particles and volatile particles.

The investigation opens up possible strategies to lessen contrail climate impacts and adopt more eco-friendly practices in aviation.

Unveiling the contrail enigma

“Soot particles, formed during fuel combustion inside aircraft engines, are known to dominate the formation of contrail ice particles,” Yu explained.

“As the aviation industry moves toward sustainable fuels and new engine technologies, soot emissions are being significantly reduced and volatile particles formed in engine exhaust plumes (after emission) become important to analyze.”

This in-depth exploration aims to augment our comprehension of the contrivance driving the number of contrail ice particles formed during flights, bringing both soot particle sizes and volatile particles into focus.

Volatile particles in contrail formation

The information gathered for this study was made possible by an ensemble that included experts from the NASA Langley Research Center and the German Aerospace Center.

The researchers conducted flight simulations utilizing data amassed from the recent ECLIF (Emission and CLimate Impact of alternative Fuels) field expeditions.

Contrary to past findings which indicated that volatile particles only came into play once soot emissions were drastically curtailed during flights, this new study suggests otherwise.

“Our research indicates that volatile particles can contribute to the number of ice particles in a contrail at medium levels of soot emissions and average temperatures in the air, extending the ranges of conditions when these particles become a factor,” explained Yu.

“This is important as we assess the climate impact of contrails, both during current flights and for future more sustainable ones.”

Shaping the future of aviation

The research focused on size-resolved particle microphysics and aerosol-cloud interactions that affect climate change. Yu has been studying the microphysics of particles in the atmosphere (including contrail formation) and their impact on the environment for over two decades.

Yu’s earlier work includes the development of a sophisticated model for simulating particle and contrail formation and he has authored numerous scientific papers on the topic.

Currently, Yu is working with a team at GE Research to gain a deeper understanding of the influence of clean aviation fuels and new engine technologies on contrail formation.

Over the past year, the team has conducted a series of experiments inside the altitude simulation chamber at NASA’s Glenn Research Center in Cleveland.

A path to reducing contrails

As the aviation industry seeks to mitigate its environmental footprint, alternative fuels offer a promising pathway to reducing contrail formation and its warming effects.

Sustainable aviation fuels (SAFs), crafted from renewable sources, not only produce fewer soot particles during combustion but also hold the potential to cut back on heat-trapping contrail cirrus clouds.

Recent flight trials have shown that jets powered by SAF blends can significantly reduce soot emissions, highlighting the importance of a wider industry shift.

However, for SAFs to make a meaningful difference, large-scale adoption across the aviation sector is essential.

Aviation practices and climate goals

Continued research will play a crucial role in driving this transformation, ensuring that each step taken aligns aviation practices with global climate goals.

With sustained innovation and commitment, a future with cleaner skies and reduced climate impact becomes more than just an aspiration – it becomes a viable reality for generations to come.

The study is published in the journal Environmental Science & Technology.

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