evidence: Contrails are trails of condensing water vapor left in the wake of airplanes. They do not contain harmful chemicals as proposed by "chemtrail" conspiracy theories, which are not supported by any evidence. Although some politicians have proposed bills to ban chemtrails or related conspiratorial concepts, they are not evidence of their existence and no such bills have been passed. Chemtrails are increasingly conflated with solar geoengineering strategies, like stratospheric aerosol injection, but these strategies are real proposals currently being explored by scientists to limit anthropogenic global warming and have not been implemented at scale.