Energy descent is another interesting angle - We know for a fact that the rate of replacement of fossil fuels is orders of magnitude below the rate at which we've been consuming it, and that there is no equal which will allow our energy-rich lifestyles to continue.

This implies at a certain point we descend to a less energy-rich lifestyle because we have no alternatives. What that descent looks like, graceful or painful, is an open question. As is exactly when it would happen - Folks were convinced peak oil was just around the corner but reality is a bit less simple.