I'll share me theory about these.
I think they are chemtrailing so we don't discover the global warming hoax and continue to sell us green products adn promoting carbon tax. Planet is getting cold says the scientists who are not in TPTB payroll. Europe faces extreme hard winters the last few years for anyone who haven't noticed yet. They chemtrailing so they can trap the carbon dioxide in our atmosphere to provoke this global warming thing for as long as they still can. There is video on utube with big pieces of Antarctic ice cut in big square straight pieces, they doing everything they can to prevent the mini ice-age we are about to see in about 2030. Here in Greece we don't have much chemtrails for a month now but the weather is already hot, they were chemtrailing us to death till a month ago and the weather was cooler than usual for Greek standards and the winter was the heaviest ever recorded this year. Sure there are others uses of these chemtrails too though.