but contrails are not made of soot, where I define soot as dark unburned carbon, contrails actual are made of water. There is also a highly likely chance I am being to literal and the word choice of soot was a bit of poetic license on the part of the author.

As a bonus consideration it might be better if they were made of soot, it would be ugly but water vapor is a tremendous greenhouse gas, several times as potent as CO2, soot blocking the sun might have more of a neutral effect, And related, we worked hard to get sulfur out of our fuels but sulfur dioxide turns out to be a negative greenhouse gas, it has a net cooling effect, I am not saying we should deliberately add sulfur back in, the downsides are too great, but it is an interesting bit of irony.