This is the same old Malthusian argument. Attempting to criticise economics on the basis of thermodynamics is akin to arguing that we should be making preparations urgently for the day the sun runs out of fuel. The scale is out by orders of magnitude. The Earth's natural resources are vast, and there is simply no danger that we are going to use them up, particularly as technology becomes progressively more efficient, and as the world's population stabilises and then (probably) gradually declines (if the global fertility rate stabilises below 2).

The reason Greenland, Easter Island and the rest collapsed can be summed up in a word - isolation. Hence they were unable to import resources or export people. The modern, globalised world doesn't suffer from this problem - heck, in a few hundred years we could even be mining asteroids or colonising Mars - so is unlikely to suffer the same fate. No, we're not individually smarter than Mayans or Anasazis, but we do have greater accumulated knowledge and superior technology.

Anyway, we're clearly not going to agree on this so perhaps we should stop flooding burntcopper's journal!