> To me a contrail will always be the byproducts of normal jet propulsion. Bingo. Contrails are a mixture of things. Even wing tip vortices create contrails. It's really about nucleation of moisture in the atmosphere. But you're right, the engines do it in much higher quantities. Just as jet engines have considerably evolved over the decades, so has their exhaust and resulting appearance. Examples of changes: FADEC (computer controlled air/fuel mixture) in the 1970s-1980s. Drastically changing exhaust composition and consistency. Anyone remember the long black exhaust plumes of jet engines? Especially as they made large power setting changes, require A/F mixture changes? https://www.youtube.com/watch?v=qmT7NwjNrLY Edit: for what it's worth, many military aircraft are still using engines based on 1960s-1980s era technology. Alloy advances in the 1980s-current. This allows for much hotter burns. Drastically changing exhaust composition and consistency. Machining advances (CNC), changing tolerances. Largely starting in the 1980s to current. This allows for much hotter burns. Drastically changing exhaust composition and consistency. Better modeling, allowing for improved combustion efficiency. This allows for much hotter burns. Drastically changing exhaust composition and consistency. Jet engines are now larger than ever. This means larger volumes than ever of moist air is now condensed and heat cycled. Making trails larger and persist longer. These have all steadily rolled out over the last 4 decades. Now people claim technology invasions created the expected results are signs of chemtrails. Just as you correctly denoted the distinction of contrails, 'chemtrail' carries with it it's own implications.