there are countless SF examples where terraforming is used against the protagonist group in some negative manner; some alien race begins some scheme to turn the planet hotter/colder/acidic/whatever and has to be stopped by some hero.
as far as being a thing outside of SF, there are lots of studies on the idea of being able to do it in one way or another to both the moon and Mars, with real life validation efforts here on Earth -- but no real practical efforts as far as I know.
p.s. the reason I avoid mentioning our efforts here on Earth changing the climate being akin to terraforming is that I think that intentionality is really the defining feature of terraforming that differentiates it from pollution or abuse otherwise.
as far as being a thing outside of SF, there are lots of studies on the idea of being able to do it in one way or another to both the moon and Mars, with real life validation efforts here on Earth -- but no real practical efforts as far as I know.
p.s. the reason I avoid mentioning our efforts here on Earth changing the climate being akin to terraforming is that I think that intentionality is really the defining feature of terraforming that differentiates it from pollution or abuse otherwise.