Wednesday, August 20, 2008

Energy Return on Investment - a simple equation behind why civilisations fail

As population densities and specialisation increase, the energy systems that sustain them have to deliver more net energy. In doing so, they allow the population to growth further and a still greater percentage of that growing population to become “non-productive” specialists.
EROEI had not been codified until recent decades, from its first beginnings all life has had to
expend energy in order to capture energy from its environment: if a fox does not obtain more
energy from eating rabbits that it consumes catching them, it will not survive long; similarly
tulips, bacteria and humans. From the days of the earliest hunter-gatherers, the nature of
human societies has been governed by their success in capturing energy (primarily food
energy) at an energy profit11.
In The Collapse of Complex
Societies (Tainter, 1988)12 and Collapse (Diamond, 2005)13 the authors examine the reasons
why societies of all sizes, from small isolated settlements up to the Roman Empire,
collapsed. Diamond identifies four reasons why societies collapse: resource depletion;
climate change; hostile neighbours; friendly neighbours. Tainter focuses on “energy gain”.
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