The conspiracy-minded will shout “chemtrails.” Of course that’s nonsense. But just what is creating these clouds?

I have to admit that I was a little taken aback when I saw these long, sinuous cloud shapes snaking across the northeast Pacific Ocean.

The image, captured by NASA’s Terra satellite on Feb. 12, 2018, covers a huge amount of territory — as is evident if you look to the extreme right, where a good portion of the west coast of North America is visible.

Before I get into what’