Why it’s illegal to use weather modification in warfare
Despite how ridiculous some rules and laws may seem, they only have to exist because someone actually did something so ridiculous. That's why it's still legal to rain death from above, just as long as that death isn't actual rain. In this case, the United States is the perpetrator, seeding the clouds in Vietnam to keep the North Vietnamese from infiltrating the South.
"This weather is crazy, as if it's happening to us on purpose!"
The idea is actually a pretty great one. Instead of bombing the Ho Chi Minh Trail into submission, they would simply render it unusable. With Operation Popeye, the United States Air Force seeded the clouds over the Ho Chi Minh Trail in an effort to make the Vietnamese monsoon season last longer, keep the trail muddy and treacherous, and prevent the North from moving men and material into South Vietnam.
From Thailand, the United States used C-130 and F-4C aircraft armed with lead iodide and silver iodide to spread into clouds above the trail. The chemicals condensed the water in those clouds, forming precipitation in the form of rain. They wanted to stop up the dirt roads used by enemy trucks and men, cause landslides, wash out river crossings, and keep the roads impassable.
The 54th Weather Reconnaissance Squadron contributed to the 2,602 cloud seeding missions flown during Popeye.
That's a lot of rain.
"I never even imagined that's what that group was doing," recalls Brian Heckman, a former Air Force pilot, "until we got over there and showed up for the briefing and then they told us what the project was all about. We just went around looking for clouds to seed."
And so Popeye continued with gusto, even though Secretary of Defense Melvin Laird had no knowledge of the program and even testified to the "fact" that there were no such programs in Vietnam before Congress. The public didn't find out about the program until the release of The Pentagon Papers, published by the New York Times and other newspapers in 1971. That's how the Environmental Modification Convention came to pass in 1977.
Chemtrails were still totally legal.
Its full name was actually the Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques, restricting "widespread, long-lasting or severe effects as the means of destruction, damage or injury." It basically says that any manipulation of weather (aka "environmental modification") as a means of destruction in wartime is strictly prohibited.
The United States was an early signatory to this agreement.