Flights that followed an avoidance path cut contrails by almost two-thirds. But getting dispatchers and pilots comfortable with these routes will be crucial.
Thanks for this important analysis. When I see a headline figure of 2% saving in GHG, I think about surface transport emissions from fossil fuelled vehicles and how easy it ought to be to save at least that amount by reducing speed limits and encouraging eco-driving. Less acceleration and braking by ‘reading the road’ instead of rushing to the next bend or junction.
Can you analyse the effect of reducing motorway speed limits to 60mph? It may happen anyway in response to Trump’s Middle East adventure.
One potential reason for the overestimate is that in-cloud contrails may play an important role. Petzold et al suggest they are the large majority of contrails, and their effect is uncertain. They may have a cooling effect by making clouds thicker. https://www.nature.com/articles/s41467-025-65532-2
Having said that, the reduction in contrails suggests the forecasting system can accurately predict when and where clear sky contrails (at least as picked up by GOES) will form. Given all the unknowns about contrails this is an exciting tool that we could learn a lot from
It would be very interesting to add a quick overview of the most effective (or at least: the first) steps governments can take to make this happen.
Also, which jurisdictions should act first or does it plausibly need collaboration via industry associations or government multilateral organisations?
I'm keen to recommend this post to MPs but a bit confused about what action to suggest that they take. (I can talk to AI but if you have thoughts yourself or links to good discussions, that would be optimal)
This below from T&E is a helpful overview of aviation’s impact on the climate, and on local air quality. Note the beneficial effect of using cleaner fuels with less aromatics content which cuts soot and helps avoid contrail production. As well as selecting flight paths that avoid the weather conditions in which contrails are formed
Thanks for this important analysis. When I see a headline figure of 2% saving in GHG, I think about surface transport emissions from fossil fuelled vehicles and how easy it ought to be to save at least that amount by reducing speed limits and encouraging eco-driving. Less acceleration and braking by ‘reading the road’ instead of rushing to the next bend or junction.
Can you analyse the effect of reducing motorway speed limits to 60mph? It may happen anyway in response to Trump’s Middle East adventure.
The reduction in contrails looks to be real, but the climate impacts are less clear. Contrails’ radiative forcing is still an open question, and even the author of the 2021 paper thinks they might have been too high. See quote in here: https://www.science.org/content/article/airplane-contrails-may-not-be-climate-villain-once-feared
One potential reason for the overestimate is that in-cloud contrails may play an important role. Petzold et al suggest they are the large majority of contrails, and their effect is uncertain. They may have a cooling effect by making clouds thicker. https://www.nature.com/articles/s41467-025-65532-2
Having said that, the reduction in contrails suggests the forecasting system can accurately predict when and where clear sky contrails (at least as picked up by GOES) will form. Given all the unknowns about contrails this is an exciting tool that we could learn a lot from
Sorry -- I didn't get to the last line which said higher fuel use.
Sid
A question -- with the lower contrails, I would expect lower fuel use -- BUT is that the situation?
If so i.e. lower cost use with the cost going up because of the war - maybe the airlines can be convinced to make the change.
Sid
The summary of the linked paper says difference in fuel use on contrail avoidance flights was not significant.
That partnership is pretty amazing
It would be very interesting to add a quick overview of the most effective (or at least: the first) steps governments can take to make this happen.
Also, which jurisdictions should act first or does it plausibly need collaboration via industry associations or government multilateral organisations?
I'm keen to recommend this post to MPs but a bit confused about what action to suggest that they take. (I can talk to AI but if you have thoughts yourself or links to good discussions, that would be optimal)
This below from T&E is a helpful overview of aviation’s impact on the climate, and on local air quality. Note the beneficial effect of using cleaner fuels with less aromatics content which cuts soot and helps avoid contrail production. As well as selecting flight paths that avoid the weather conditions in which contrails are formed
https://www.transportenvironment.org/topics/planes/contrails
Sorry Hannah............this is rubbish !
Hannah,
it's great that you have such considered and evidence based responses to your careful, insightful amd evidence based postings.
I think it's a great article, and would really like some airlines to take it up.
I can easily see it featuring in someone's advertising campaign.
"It's the things you can't see, that make XXXX your choice of airline important! !
:)
Is it possible that generating con trails generates a little extra drag on the aircraft?
I assume contrails occur in spaces with higher relative humidity, and the air is more dense🤔
Avoiding such spaces should save fuel 🤔
Surprisingly, air density decreases with higher humidity.
(the molecular weight of water is lower than nitrogen or oxygen)