evidence: PolitiFact has debunked other claims involving "chemtrails." The evidence remains: chemtrails aren’t real. A 2016 study evaluated claims of a secret large-scale atmospheric program, commonly referred to as "chemtrails" or "covert geoengineering." The authors from Carnegie Science, University of California, Irvine and the nonprofit organization Near Zero surveyed atmospheric chemists who specialize in condensation trails and geochemists. [...] Contrails — short for condensation trails — are "line-shaped clouds sometimes produced by aircraft engine exhaust," as defined by experts at the Environmental Protection Agency, the Federal Aviation Administration, the National Oceanic and Atmospheric Administration and NASA.