Technically you cannot use weather modification as a weapon but when has the rule of law stopped crazy people.

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

To restate I am all for being able to help the planet, mitigate our impact using new greener technologies and changing our habits, however this needed to be done a long time ago and trying to fix our current problems with the band-aide of Geo-engineering I personally believe is a futile effort.