Consider that Earth had way higher carbon levels during hothouse periods like the Carboniferous. In the limit, then, "there is no hope" anyway since it's a natural cycle. We are leaving a recent ice age and are due for another hothouse phase anyway. We either cope or we die, as a species. I'm really confident we'll cope. I predict that the only thing that'll end us is ourselves, not with carbon emissions but with bioweapons.