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Comment by phkahler | Hacker News Reader

Air travel is more important because of the water vapor far more than the carbon.

The week following 9/11 was dramatically different. NASA recorded the change in daily temperature range. Less significantly, we had crystal clear skys where I live - for a week!

Water vapor can also seed cloud formation. Air travel causes a daily cycle in this, which might just keep more heat in at night.

You can look at data and see the temperature rise along with energy use (CO2). But to compare it with the rise in air travel is also informative. IIRC there is even an uptick of both during WWII.

But y'all can keep screaming 'bout CO2 till the cows come home. It may be that we really need coal fired airplanes that dont emit water vapor, just more CO2.

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> "The week following 9/11 was dramatically different. NASA recorded the change in daily temperature range. Less significantly, we had crystal clear skys where I live - for a week!"

Do you have links for this?

https://web.archive.org/web/20160411094048/http://www.atmos....

https://www.nature.com/news/2008/081231/full/news.2008.1335....

The second link actually states the opposite: "A new analysis now claims that altered US temperature patterns during the three flight-free days can be explained by natural variations in cloud cover, rather than the absence of planes."

Just imagine how this will get magnified and drive the world nuts when half the things we try to do to tackle climate change end up being plausibly explainable by natural variation. It's already a hard enough problem to solve without natural variance being thrown into the mix.

But that's not conclusive either. There is this:

The research by Hong and his colleagues, published in Geophysical Research Letters, follows other studies arguing that the September 2001 temperature variations can be explained by the clear, dry weather on the crucial days4, and that climate-modelling results do not support the contrail effects claimed by Travis's group5.

I contend the clear dry weather was a consequence of the lack of planes. It sounds the one of the original authors does too.

All I know is the weather here was beautiful. And very uncharacteristically so. Unfortunately nobody is going to repeat the experiment by grounding the entire fleet for 3 days just to test it.

Minnis, Patrick, J. Kirk Ayers, Rabindra Palikonda, and Dung Phan, 2004. "Contrails, Cirrus Trends, and Climate". Journal of Climate Vol. 17, No 8, pp. 1671-1685, April 15, 2004

doi:10.1175/1520-0442(2004)017<1671:cctac>2.0.co;2

https://journals.ametsoc.org/doi/pdf/10.1175/1520-0442%28200...

I remember hearing about this at the time. Some links I just looked up:

https://www.int-res.com/articles/cr2002/cr2004/26/c026p001.p...

https://www.pbs.org/wgbh/nova/article/contrail-effect/

I lived in Dallas at the time. It was eerie having a few days of No air traffic; and indeed the air was much less visible (so presumably cleaner).

Note also that cloud cover increases albedo, namely how much light is reflected back to outer space. Does that mean contrails are good for the environment? Probably not, but this a very complicated system that one can’t make simple statements without sitting down and doing the math.

Today was a beautiful clear day too though, September tends to do that.

I'd think the vapor trails would also reflect the suns heat so help cool the day time temperatures.

How would a coal fired aircraft not emit water vapor, less hydrogen in the fuel?

At least the water issue goes away as soon as you stop.

Edit: Discussion with a colleague lead to an estimation of a residual time of ~10-30 years of the heat caught in the system, so 'soon' should be understood like that.

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