alt Hacker NewsPeople who believe in "chemtrails" are (in my un-scientific survey) pretty likely to be conspiracy enthusiasts ("cranks", "crazy", etc.).
But they're not wrong that the stuff coming out of the back of jet aircraft is changing the climate.
Small, localized weather engineering programs have long been real (cloud seeding), and planetary-scale climate engineering projects are now openly discussed by governments. E.g. https://www.epa.gov/geoengineering/about-geoengineering "Types of solar geoengineering techniques include: Stratospheric Aerosol Injection (SAI) – adding small reflective particles to the upper atmosphere (stratosphere) to reflect incoming sunlight. Sulfur dioxide (SO2), one of the types of chemicals considered for SAI, can chemically react in the stratosphere to form reflective sulfate aerosols."
Except "stuff" isn't coming out of the back of aircraft: they're talking about aircraft contrails which is just condensed water vapor from wingtip turbulence.
The people who claim they're monitoring chemtrails aren't even watching aircraft which are deliberately dispensing payloads, because it just isn't that common in the first place (unless you go out and watch crop dusting, but then you can also just see the guy land, get out, and talk about it).