The Silent Elephant

In his book The Great Warming: Climate Change and the Rise and Fall of Civilizations, eminent anthropologist  Brian Fagan describes the period from about 800 to 1200 AD, in which a small increase in average global temperatures resulted in a warmer, greener and wetter Europe and generations-long droughts in the Americas and parts of Asia.  The more hospitable growing seasons in Europe helped spark the early Viking settlements in Greenland and Vinland (northeast North America).  Erratic and lengthy droughts were instrumental in the collapse of the Maya civilization, the disappearance of Anasazi communities, and the abandonment of the great Ankgor Wat complex.