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Comment by extropy | Hacker News Reader

I'm not following the logic why contrails cause net warming.

Why nuclear blasts - that also introduce lots of particles in atmosphere cause a cooling effect - "nuclear winter"?

Water vapour absorbs the thermal radiation (heat trying to escape earth) better than it absorbs sunlight (heat trying to enter earth). Therefore, the more water vapour in the atmosphere, the stronger the greenhouse effect.

https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_...

https://en.wikipedia.org/wiki/Greenhouse_effect

In this case I believe it's not water vapor, but rather reflection of IR from ice crystals.

They don’t cause net warming, it’s transient. If we stopped flying tomorrow it would go away quickly. But we keep flying.

But even with that the amount of warming this continuous effect creates is quite small and negligible compared to greenhouse gas warming and isn’t really worth talking about.

I think this link hit HN in part due to the new Simon Clark video on contrails which mentioned it. Simon discusses the claim that contrails can be avoided for a small fuel penalty, reducing the overall effect on climate change a given flight would have. Apparently some airlines are already exploring this and Google includes contrail impact estimates on their flight search. So maybe it is worth talking about.

https://youtu.be/QoOVqQ5sa08

The difference is that water vapour is a greenhouse gas. IIRC the net warming effect of clouds is a function of altitude.

Yes, also a mushroom cloud from a nuclear blast blocks light from passing through which reduces heating on the ground whereas contrails are thin which lets light through but still retains heat below them.

It's not specifically about logic. It is possible to model and measure the radiative effect of contrails.

I have no doubt that nuclear testing has affected the environment far more than is being let on. These experiments by their nature were classified. Who's to say they weren't a factor in helping create the ozone hole?

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