Scientific debate is getting heated over what to do about airplane contrails — the wispy lines of water vapor you often see trailing behind a jet.
Those harmless-looking vapor trails sometimes spread out to form thin cirrus clouds. Environmental activists and nonprofits focused on climate change routinely assert contrails contribute more to global warming than the carbon dioxide emitted from jet engines.
The aviation industry, under pressure to do something, has stepped up research into contrails.
In October, Boeing and NASA conducted flight tests out of Everett with a NASA DC-8 research plane flying behind a 737 MAX 10 to sniff its exhaust and analyze its contrails to test if so-called sustainable aviation fuel, or SAF, may reduce their incidence.
And Google, in a partnership with researchers at Breakthrough Energy — the Seattle-based climate action research group founded by Bill Gates — conducted a small experiment with American Airlines to test whether commercial pilots could avoid regions of the atmosphere likely to induce contrails. A larger trial with multiple air carriers, including Alaska Airlines, is planned for next year.
But last week, the consensus that contrails are so bad for the planet that we need to quickly find ways to reduce them was shattered.
David Lee, author in 2021 of the most influential study of the impact of aviation on the climate and chair of the U.N. Intergovernmental Panel on Climate Change's aviation working group, published a new and trenchant assessment of the myriad scientific uncertainties around the subject.
Co-authored by prominent U.K. climate researchers, the paper concludes that "the fundamental premise" that contrails are important enough to mitigate "is not yet established."
Beyond the uncertainty in the scale of the contrail warming effect, Lee points to a related cooling impact that could potentially cancel it out.
Lee argues that the data on aviation's non-CO2 impacts — chiefly the contrails and the effect of engine emissions on cloud formation — is so uncertain that any action to mitigate them "may be of limited effect or have unintended consequences."
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