They would not have made an agreement like this if they did not already have the ability to control the weather. It is a fact they used it during the Vietnam war to cause flooding. This agreement talks about using weather modification for war and hostile purposes but doesn’t say anything about using these weapons against states they want to harm or people they wish to harm for political reasons.

https://lawyerlisa.substack.com/p/the-un-has-a-treaty-about-using-weather?