Silent Running...
Dern was a tree hugger who killed three people in that movie. But that movie popped into my head too.
Bruce was a car mechanic, innocently in the wrong place, the Clark Street garage when the St Valentines Day thing happened.
Yea, but it was in saving the last North American ecosystem dome.
In reality the premise stretches suspension of disbelief for me now days. You would probably need to reliquify the surface down to at least a mile to sterilize the planet and getting rid of surface life would need pretty close to that...