Entry 4: The Complex Nature of Contrails
While looking for answers on the relationship between contrails and time of day, I stumbled across an article from science.org.
It1 discusses how contrails are considered to trap large amounts of heat, which can be up to around 3x more heat than aviation’s CO2 according to some studies. It also shares how researchers have collaborated with airlines recently to avoid contrail formation by modifying flight routes to avoid certain altitudes based on weather data, like the trial Google ran with American Airlines in 2023 with 70 flights2 and later in 2025 in 2,400 transatlantic flights3.
The article then talks about how recent studies have identified some limitations to this approach. To summarise some of the main points:
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Small-scale trials from 2021 showed some weather models only predict where contrails form 1/5th of the time due to the contrail field being “data-starved”1.
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One study found over 80% of contrails in their dataset formed in existing clouds rather than in clear skies4. These could have a reduced warming effect, or even a cooling effect, which needs to be accounted for in contrail-avoidance schemes
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Another study found that contrail warming was not 3x that of CO2, but rather 2/3rd, suggesting a smaller impact than previously perceived5
To relate this back to my posts so far, in those spots such as the Southern Ocean where a high contrail forcing index is found, we should consider whether those contrails would form inside existing cloud cover, as this might cause the warming effect to be lower than the CFI values suggest.
My main takeaway from this article is understanding how complicated contrail formation is and how much more knowledge is needed to better understand their climate impacts, carefully balancing fuel usage and the warming impacts from each contrail region. What this means for me: it motivates me to keep analysing data in Australia, an underexplored region of the world, and share these findings.
References
[1] Voosen, P. (2025). Airplane contrails may not be the climate villain once feared. Science, 390(6776).
[2] Elkin, C., & Sanekommu, D. (2023, August 8). How AI is helping airlines mitigate the climate impact of contrails. Google Blog.
[3] Google Research (2026, March 19). Our new study explores how AI can reduce the climate impact of air travel. Google Blog.
[4] Petzold, A., Khan, N. F., Li, Y., et al. (2025). Most long-lived contrails form within cirrus clouds with uncertain climate impact. Nature Communications, 16, 9695.
[5] Bickel, M., Ponater, M., Burkhardt, U., Righi, M., Hendricks, J., & Jöckel, P. (2025). Contrail cirrus climate impact: From radiative forcing to surface temperature change. Journal of Climate, 38(8), 1895–1912.