We are part of the environment. Other people are part of my environment. I am part of the environment of other people and of many other organisms such as the bacteria that live in my gut, the birds that nest in my building, or the plants that live in some distant rainforest. The question whether we have obligations towards "the environment" doesn't make sense.
Climate change is not the last environmental burden we will place on the world and probably not even the biggest such burden, but fewer people does mean less human pressure along many environmental dimensions, present and future."Burden?" "Human pressure?" I understand that these are just metaphors, but metaphors for what? The choice of words suggests a world in which "the environment" is better off if not touched by us the outsiders, and the well-being of "the environment" is above our well-being. Maybe Cowen and those who speak in similar terms mean some other thing. If so, why don't they choose other metaphors?