You can't undo what's already been done, but if you want to stop damaging it further, or if you don't want to see our civilization collapsing/being seriously disturbed by running out of fossil fuel and therefore you want to go all green before that happens, then yes, you can build enough nuclear plants and absolutely positively have to.

This book [0] goes through math of pretty much all energy sources and one of the conclusions the author reaches is that if you want to cover all of our power needs with green energy, renewables alone ain't gonna cut it.

[0] - http://www.withouthotair.com/