But ones that last a couple centuries might be good. I would think that sustainability is a relative index, rather than an absolute one.
Societies operating on solar energy are more sustainable than societies operating on fossil fuels.
It makes a reasonable effort to preserve the existing resource base. Based on this criterion, no adaptation could ever be identified. Graber I think it can be identified. I think it may be attained and may survive, but it will take work. The map is not the territory.