] As the planet's carrying capacity shrinks, an ancient
] pattern reemerges: the eruption of desperate, all-out
] wars over food, water, and energy supplies. As Harvard
] archeologist Steven LeBlanc has noted, wars over
] resources were the norm until about three centuries ago.
] When such conflicts broke out, 25% of a population's
] adult males usually died. As abrupt climate change hits
] home, warfare may again come to define human life.

Fortune.com: Grim Pentagon Climate Change scenario