Everyone has seen contrails produced by jets. I recently learned that ocean-going ships can also produce contrails that can be seen by looking down from above:
To produce contrails, you need both a lot of water vapor in the air and some aerosol particulates to act as nucleation sites to form the tiny water droplets that appear as clouds. Jet exhaust supplies both of these ingredients, so the water vapor freezes into ice crystals to form the visible trails. Ship contrails are produced because tiny aerosol particles in the ship’s exhaust provide condensation nuclei for water droplets to form in air that is likely already super-saturated with water vapor. It turns out that over the open ocean, there is often a lot of water vapor available but a shortage of tiny particulates to act as nucleation sites. The ship’s exhaust provides the particulates along its path and clouds of water droplets form.
Jet contrails have gathered attention recently concerning their relationship to global warming. Do they cool the planet because they reflect sunlight back out to space, or do they warm the planet by trapping heat? According to this article, the balance tips slightly towards warming, but only slightly.
I would think (but I don’t know) that ship contrails might be different because they are lower in the atmosphere, so maybe they reflect less and blanket more? It mostly doesn’t matter because ship contrails only form under the right conditions, and those conditions usually mean that there are some clouds nearby anyways.
Conspiracies section we’ll address those there.
