Before COVID-19 tens of thousands of cargo ships criss-crossed the oceans daily, creating puffy white cloud trails in the sky that look much like the contrails from jet planes. They reflect solar energy and help to bring down global temperatures. Ship clouds form when water vapor in the air condenses on tiny pollutant particles in the exhaust from ship engines. They can remain in the air for hours. Climate models show these clouds can have an unusually large effect on the climate.
Climate Crisis Blog
