evidence: These days it's a common sight: hazy streaks crisscrossing the sky left from passing aircrafts. But many people believe there’s something more going on. Dubbing the contrails "chemtrails," conspiracy theorists have claimed that these trails of condensed water are part of a secret program to control the weather, change the climate or control our minds. [...] The chemtrails craze likely originated with a 1996 report from the Air Force called "Weather as a Force Multiplier," which speculates how the military could develop weather modification technology by 2025, report Annalee Newitz and Adam Steiner at i09. A patent filed in 1991 for a technique of seeding the upper atmosphere with particles that could reflect sunlight and slow global warming also intrigued theorists. Combined with anecdotal tales of plants dying and people getting sick after planes left contrails above their homes, the conspiracy theory coalesced and took off on the internet in the late 1990s. [...] So, if it’s not a government program, why do many people claim to see more and more contrails? Emerson says airplane contrails are likely lasting longer than they used to due to changes in jet engine technology. In addition, an increase in air travel over the last couple decades could also be fueling the belief in chemtrails, says Caldeira, and atmospheric changes from global warming may cause the artificial clouds to linger longer than they used to.