When it comes to damaging the environment, bet on destructive systems to do more harm than countable events.
This includes invasive species, urban sprawl, and overfishing in one group and volcanoes, tidal waves, nuclear tests and oil spills in the other. I think it's more important than the natural/man-made dichotomy that is the way I am instinctively inclined to think of these things.
On the other hand when damaging the environment bet on living humans doing more harm than dead humans. The best thing for the environment would be the utter annihilation of humanity - a rather destructive process. Mind you I'm not going to make bets about that...
A reminder for everyone: on this day in 1983, Stanislav Petrov saved the world.
It occurs to me this time around that there's an interesting relationship here - 9/26 is forgotten, while 9/11 is remembered. Do something charitable, and not patriotic, sometime today.