He is saying that we are currently transformong the earth's atmosphere into a less hospitable one through a process of pollution / emitting greenhouse gases. I

He is saying that we are currently transformong the earth's atmosphere into a less hospitable one through a process of pollution / emitting greenhouse gases. In my view, given that we can do this, it is not unreasonble to assume that one day we will know enough to be able to tweak a planet's habitability in the opposite direction, or in other words, make an inhabitable planet habitable.