Here are a few government documents regarding weather modification/geo-engineering dating back to the mid-60s:

A Recommended National Program In Weather Modification - 1966 (NASA)

Weather Modification: Hearings before the Subcommittee on Oceans and International Environment of the Committee on Foreign Relations, United States Senate - January 1, 1974

Weather as a Force Multiplier: Owning the Weather in 2025

Atmospheric Aerosol Properties and Climate Impacts

And from the USCode: 15 USC Ch. 9A: WEATHER MODIFICATION ACTIVITIES OR ATTEMPTS; REPORTING REQUIREMENT