Noticed them in Europe's skies, too. Still haven't made up my mind whether I believe the documentaries (The 'What in the World Are They Spraying?' series).
I once saw one in Glasgow, Scotland that you could call a "classic" if you go by the documentary - slowly spreading in that strange pattern. I couldn't believe it as I watched it unfold. Tricky topic.
All I know is that several years ago they started to last longer, then get laid in patterns. Now we have gone from 90% clear and sunny days to it being notable when it is not overcast. So regardless of the motivation, reason or cause, there is clear correlation and something needs doing about things.
Haha, up here in Scotland we wouldn't really notice a difference - shades of grey usually. Blue sky is a rare occasion by default. We cheer each other up by saying, "Oh look, there's a bit of blue!" :'D Ah well, maybe not quite as bad. We get a week's allocation of summer each year.
But yeah, the trails are a worrying man-made phenomenon.
Here in Canberra we rarely had overcasts unless it was actually one of the 6 days of the year allocated for rain. We went the better part of the 90s and early 00s with nothing. Used to say the only good thing about Canberra winters was, it might be cold but at least it is still nice and sunny. We are on the edge of the Australian outback and it was always clear and sunny here. Was...