Yes, we've been "terraforming" it. But not in a way that's good for us, I think. Not to mention all the other species that have evolved for pre-human conditions

Yes, we've been "terraforming" it. But not in a way that's good for us, I think. Not to mention all the other species that have evolved for pre-human conditions. And have increasingly experiencing conditions for which they're not well adapted. Worse, conditions that have been changing far too fast for evolutionary adaptation. Or even mass migration. So they're getting screwed. What we're now calling the Anthropocene Extinction Event. So perhaps "terraforming" isn't the appropriate term. Maybe more like "un-terraforming". If CO2 goes runaway enough, we might even wipe out enough photosynthetic capacity (especially in the oceans) to undo the Great Oxygenation Event. And make the planet safe for anaerobes again.