They form due to condensing water vapor as ice crystals, it’s dependant on temperature, humidity and pressure. It’s potentially the largest climate change factor from airtravel - not the burning of fuel, due to its own greenhouse effect (at least in the short term). But the jury is still out on that. The UK and presumably other nations are looking at reducing contrails through routing (at different altitudes in different weather conditions etc). So I guess this is accidentally not a bad idea but for the wrong reasons.

[–] quarrk@hexbear.net 11 points 4 days ago (2 children)

How does the water vapor affect the climate?

[–] Palacegalleryratio@hexbear.net 17 points 4 days ago* (last edited 4 days ago)

Because unlike water vapour in air, the ice crystals in the contrail reflect light (which is why we can see them) which causes a radiative forcing effect preventing infrared radiation leaving the earth, causing heating.

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[–] D61@hexbear.net 1 points 3 days ago

Adds mass to a quantity of air, more mass means that quantity of air can absorb more heat and hold on to that heat longer.

Ice crystals, like Palacegalleryration pointed out, work like tin foil in an oven. The crystals work like a blanket that reflects some parts of sunlight back to Earth instead of continuing out to space.