How we design our answers to the immediate crisis will have, it seems to me, much to do with the conditions faced by our great-great grandchildren in the next couple centuries. Just as we're learning that the Great Wager is a one-time shot (that we only have enough resources and biocapacity to build this new civilization once, so we'd better get it right the first time), barring some magical technological breakthrough (and pinning our hopes on that seems a bad bet for reasons we'll pick up another time) those to follow after probably will have, to some large extent, work within a tighter set of ecological limits and with the already-embedded energy and resources of the civilization we design this century. It seems to me extremely unlikely, in other words, that humanity in the 22nd century will be in a position to toss it all and start over (instead, their frontier may be the ruins of the unsustainable aspects of the world we're building today, their resource base our dumps and disaster zones).
Worth having a read/browse - perhaps add a comment or two....
Read article - 'What are the Sustainability Implications of Peak Population?'