Jet fuel is a hydrocarbon, and when it burns, it produces water vapor as one of its byproducts. Some people believe that these persistent contrails are not just water vapor, but something else entirely, something more nefarious. Some theories suggest that these persistent contrails are actually “chemtrails,” containing harmful chemicals deliberately released into the atmosphere. Contrails do have an impactEven if they’re just water vapor, contrails can still affect our environment. Now, cirrus clouds, both natural and the ones formed from persistent contrails, tend to be pretty good at trapping heat.