Going under a variety of names - atmospheric geoengineering, weather modification, solar radiation management, chemical buffering, cloud seeding, weather force multiplication - toxic aerial spraying is popularly known as chemtrails. However, this is merely one technique employed to modify weather. The practice of environmental modification is vast and well funded.
As yet, no one has been able to determine exactly WHY geoengineering operations are taking place, short of the official response provided by advocates of GeoEngineering, which in the first place deny any current operations are taking place, however they insist human intervention is needed because of global warming and increasing levels of CO2. The very same CO2 that is needed for life to subsist on planet earth.
Check out the links below for books about Chemtrails AKA GeoEngineering.