Cloud seeding[edit]
Since the 1940s, cloud seeding has been used to change the structure of clouds by dispersing substances into the air, potentially increasing or altering rainfall. In spite of experiments dating back to at least the start of the 20th century, however, there is much controversy surrounding the efficacy of cloud seeding, and evidence that cloud seeding leads to increased precipitation on the ground is highly equivocal. One difficulty is knowing how much precipitation might have fallen had any particular cloud not been seeded. Operation Popeye was a US military rainmaking operation to increase rains over Vietnam during the Vietnam War in order to slow Vietnamese military truck activity in the region. Rainmaking is not climate engineering, which seeks to alter climate, but a form of weather modification, as it seeks only to change local weather.