What is geoengineering? It’s the large scale intervention and manipulation of the global climate system through various means, the most popular seems to be spraying reflective substances into the air via aircraft or balloons in order to reflect the sunlight back into space.
http://www.collective-evolution.com/2018/05/10/what-most-people-call-chemtrails-could-kill-tens-of-thousands-of-people-says-harvard-professor/