[DemocracyFTW2]

Wikipedia[1] states it very clearly:

> It is considered that the largest contribution of aviation to climate change comes from contrails. In general, aircraft contrails trap outgoing longwave radiation emitted by the Earth and atmosphere more than they reflect incoming solar radiation, resulting in a net increase in radiative forcing. In 1992, this warming effect was estimated between 3.5 mW/m2 and 17 mW/m2. In 2009, its 2005 value was estimated at 12 mW/m2, based on the reanalysis data, climate models, and radiative transfer codes; with an uncertainty range of 5 to 26 mW/m2, and with a low level of scientific understanding. [...] Contrail cirrus may be air traffic's largest radiative forcing component, larger than all CO2 accumulated from aviation, and could triple from a 2006 baseline to 160–180 mW/m2 by 2050 without intervention.

What I can say is that even in a place with moderate air traffic, you get to see lots of contrails crisscrossing the sky on some days; in places near busy airports I hear that a sizable fraction of all cloud cover is due to lingering contrails.

[1] https://en.wikipedia.org/wiki/Contrail#Impacts_on_climate

[zahlman]

> Contrail cirrus may be air traffic's largest radiative forcing component, larger than all CO2 accumulated from aviation, and could triple from a 2006 baseline to 160–180 mW/m2 by 2050 without intervention.

Okay, but how does this compare to the forcing of the overall anthropogenic CO2 accumulation?

[gs17]

According to Wikipedia:

> For carbon dioxide, the 50% increase (C/C0 = 1.5) realized as of year 2020 since 1750 corresponds to a cumulative radiative forcing change (delta F) of +2.17 W/m2

[bityard]

> in places near busy airports I hear that a sizable fraction of all cloud cover is due to lingering contrails

Hmm. I don't know about that. My understanding is that contrails only (or mainly?) form at higher altitudes. Most of the traffic around a busy airport is low-altitude take-offs and landings. I live practically next door to a busy international airport and can't say I ever notice contrails, except for a few off in the distance around dusk.

I notice a lot more contrails when I'm out in rural "flyover country", but that might also just be because you typically get to see much more of the sky when you're out in the middle of nowhere.

[DemocracyFTW2]

Do you ever see this kind of sky https://www.spiegel.de/wissenschaft/technik/kondensstreifen-... ? That's over Frankfurt, Germany's busiest airport. Also from the 2020 article (v. G. tr.):

> Researchers believe that the ice clouds created by contrails have contributed more to the rise in global temperatures in recent years than all the CO2 released into the atmosphere since the beginning of aviation. The annual increase in air traffic and flight routes at ever higher altitudes are particularly contributing to the formation of ice clouds. At high altitudes, contrails can combine with icy cirrus clouds and thus remain in the sky for up to 18 hours.

[dylan604]

For those curious about the image, but not curious enough for whatever nope not signing up modal:

https://cdn.prod.www.spiegel.de/images/fe93cb37-2540-4fbb-a4...