[dylan604]

"Why aren’t we doing more to eliminate contrails?"

I'm just having a hard time groking that contrails are really that impacting. TFA just quotes a bunch of numbers, but does not actually discuss how the numbers were derived. Maybe I've just been around too many people into Chemtrails, but this just reads to me as an offshoot of that type of thinking.

[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...

[roadside_picnic]

Contrails observably suppress the Diurnal Temperature Range (i.e. they make it cooler during the day).

How could this be observed you might ask? It turns out there was a study done immediately after the grounding of airplanes during the September 11th, 2001 events to take advantage of this unique incidence of effectively halting all air transportation for a few days [0]

0. https://journals.ametsoc.org/view/journals/clim/17/5/1520-04...

[readthenotes1]

There's some anecdata from 9/11

https://globalnews.ca/news/2934513/empty-skies-after-911-set...

[dylan604]

The NASA image does make contrails look much larger than say from the ground, but even in the same image true cloud cover is clearly more complete than all of the contrails combined from the same image

[jvanderbot]

Well some of us are doing things to eliminate contrails ... (Shameless self promotion of my employer)

[burkaman]

It links to this post which has a little more technical explanation: https://notebook.contrails.org/comparing-contrails-and-co2/

And also this paper which is a very in-depth technical explanation: https://www.sciencedirect.com/science/article/pii/S135223102...

I understand why you're reminded of chemtrails, but it is not crazy or conspiratorial to look at these giant lines in the sky and think "those things must be doing something". You can't then make the leap to "it's intentional and it's a biological weapon to control my mind and I don't need any evidence to believe this", but you can take the next step of looking into decades of research on the topic and deciding if the conclusions make sense to you.

[dylan604]

Where I'm from, contrails are so small and irrelevant compared to the giant cumulonimbus clouds that form in the high heat and humidity. It's like tears in the rain in comparison.

[burkaman]

I don't know what to tell you, they are not irrelevant even if they visually look irrelevant from where you are. Small things can have a big impact, CO2 is only ~0.04% of the atmosphere (compared to the ideal level of ~0.03%) and it's causing us major problems.

[pixl97]

Right there is local climate too that has different effects.

Imagine a large city in an area that is always cloudy versus one in a sunny desert. They are both the same size, but the one in the desert is going to have an absolutely massive amount of evening heat release due to the urban heatsink effect.

[grues-dinner]

> not crazy or conspiratorial to look at these giant lines in the sky and think "those things must be doing something"

I think more accurately it's not crazy to think they might be doing something. I could equally be convinced if researchers crunched the numbers and concluded they might seem big but they're negligible on a global scale. In fact the same figure of "only 3%" of flights really have an effect" could easily have cut the other way.

A bit like how wind turbines look huge and numerous but are (as yet and for the foreseeable future) completely negligible on the scale of global wind power.

In fact plenty of times much closer to home, thinking "this very obvious thing must be having an effect" and failing to verify that it actually does has screwed me over repeatedly in everything from bug fixing to installing floorboards.

[burkaman]

Sure, I meant "must be" in the colloquial sense of "I have a suspicion", not "I am absolutely certain". Like "it's 5pm, must be a lot of traffic on the highway right now". If traffic turned out to be light I would be mildly surprised, update my assumptions and move on with my life.

[grues-dinner]

Fair enough, it was pedantic. But the distinction is exactly where conspiracists come unstuck.