Is there a treaty for weather weapons?

 

 https://www.sciencehistory.org/stories/magazine/manufacturing-the-weather/

The ENMOD Convention is specifically intended to prevent use of the environment as a means of warfare, by prohibiting the deliberate manipulation of natural processes that could produce phenomena such as hurricanes, tidal waves or changes in climate. 

https://en.wikipedia.org/wiki/Environmental_Modification_Convention