Preprints
https://doi.org/10.5194/egusphere-2025-3739
https://doi.org/10.5194/egusphere-2025-3739
22 Sep 2025
 | 22 Sep 2025
Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

Observing long-lived longwave contrail forcing

Aaron Sonabend-W, Scott Geraedts, Nita Goyal, Joe Yue-Hei Ng, Christopher Van Arsdale, and Kevin McCloskey

Abstract. Contrail microphysical simulations and climate simulations have indicated that contrail cirrus cause a substantial fraction of aviation’s climate impact. While the approximations and parameter selections in these simulations have been well-validated over the past two decades, the heat trapping of contrails has not been observed using satellite data beyond a few hours. This is because contrails lose their linear shape after a few hours, making them difficult to distinguish from natural cirrus clouds. Here we provide satellite-driven analysis of long-lived heat trapping by contrails over North and South America. We aggregate a dataset of GOES-16 estimated outgoing longwave radiation and advected trace density of flight paths, and apply causal inference to discern the effect of contrails while controlling for radiative and cloud confounders. As a means of validation, we also generate synthetic datasets with known ground truth, and confirm that applying the causal inference method is able to recover the synthetic ground truth. Since this method yields an estimate which has some differences from both “instantaneous radiative forcing” (iRF) and “effective radiative forcing” (ERF) estimates which have been reported in the literature so far, we introduce the new term “observational radiative forcing, 12 hours” (oRF12). Our analysis estimates the longwave oRF12 from contrails over the Americas averaged 46.9 gigajoules per flight kilometer (95 % CI: 35.8 to 58.0 GJ/km) during April 2019 to April 2020.

Competing interests: Authors are employees of Google Inc. Google is a technology company that sells computing and machine learning services as part of its business.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Aaron Sonabend-W, Scott Geraedts, Nita Goyal, Joe Yue-Hei Ng, Christopher Van Arsdale, and Kevin McCloskey

Status: open (until 27 Oct 2025)

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Aaron Sonabend-W, Scott Geraedts, Nita Goyal, Joe Yue-Hei Ng, Christopher Van Arsdale, and Kevin McCloskey

Model code and software

Example code Aaron Sonabend-W, Scott Geraedts, Nita Goyal, Joe Yue-Hei Ng, Christopher Van Arsdale, and Kevin McCloskey https://github.com/google-research/google-research/tree/master/contrails_longwave/

Aaron Sonabend-W, Scott Geraedts, Nita Goyal, Joe Yue-Hei Ng, Christopher Van Arsdale, and Kevin McCloskey

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Short summary
Airplane condensation trails trap heat, but the full warming effect has been hard to measure with satellites as they quickly blend with natural cirrus clouds. Our new method isolates their long-lived impact, estimating the effect of flight paths on satellite measurements of heat leaving the Earth. We found contrails trapped 46.9 gigajoules of heat per kilometer flown over the Americas, providing a crucially missing observation-based estimate of a large portion of aviation's environmental impact.
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