For me this is an important book at an important time. The author uses the analogy of the Roman empire's collapse to show the warning signs facing global civilisation by explaining how, like an ecological system, a complex civilisation is dependent on energy flows. And the more complex it becomes, the more energy it requires to maintain that complexity, but with diminishing returns. He uses Buzz Holling's "adaptive cycle" model, developed through study of forest ecology, to explain how a system increases its complexity and potential over time and eventually loses its resilience, its ability to withstand shocks. At this phase in the cycle the system is vulnerable and either catastrophically collapses into lower states of complexity - like the Roman empire - or deliberately does so in a more controlled manner in order to increase resilience. The latter path is the author's advice to us.

He lists the following "tectonic stresses" that he believes are building inexorably below the foundations of our societies: 1) population stress - not only growth but differing rates of growth between rich and poor societies; 2) energy stress - above all "peak oil" which seems to be almost upon us now; 3) environmental stress; 4) climate stress; and 5) economic stress resulting from instabilities in the global economic system and ever-widening wealth disparities within and between societies. Homer-Dixon's argument is that our global societies, tightly coupled and interdependent as they are and testing the limits of the ecosphere as they are, are vulnerable to synchronous shocks along any of the five fault lines outlined above.

The last chapters' posture is optimistic, but the project to restore resilience that he proposes is daunting, requiring global co-operation on an unprecedented level. Example: "...a value system that makes endless growth the primary source of our social stability and spiritual well-being will destroy us", but "growth, even in already obscenely rich societies, is sacrosanct." Can you envisage our political and economic elites willingly leading our societies into a different paradigm? I can't. ( )

The author is an expert on energy resources and its relationship to society. He writes about complex systems and their eventual failure being a time of danger and renewal. He compares todays global interconnected civilization to Rome in detail. Well thought out and written though at times too detailed. Definitely thought provoking. ( )

I'm not sure what it says about me to reveal that there wasn't much of the gloom and doom in the early part of the book that I didn't already know about. And having attended a great talk by Homer-Dixon about 8 years ago based on his last book, I had a pretty good idea of his 'take' on things. I'd heard much about the optimistic bent of this book, though (contrasting with Wright's Brief History of Progress, for example, with nary an optimistic note in sight), and so it might have been because of this that I was surprised that the optimistic message that we can see collapse as an opportunity for renewal as a kind of a tack-on. Sure, it's possible that we will come out of the next century in better shape than we are now, but it just doesn't seem likely to me. Still, I liked the book quite a lot. I liked some of the cleverer examples and points of comparison between our civilization and Ancient Rome. And it will be etched in my mind forever that a single tank of gas has the energy equivalent of 2 years of human labour. Kind of puts a new cast on that 20 mile drive for a can of coke that I used to find reasonable years ago when I lived far in the country. ( )

Great overview of challenges to the world based on the fact that we live in a complex, connected world (this is explained in the book, including why this is a bad thing). Discusses the normal cycles of systems and potential hot spots to watch in the future ( )

http://ryanschultz.vox.com/library/post/brief-review-the-upside-of-down-catastro... ( )