Brian Fagen is a emeritus professor of anthropology at the University of California, Santa Barbara.
In his talk Fagan emphasized a wide view of human history as it unrolls in the landscape of climate. … we can see evidence from ice cores, tree rings, fossil pollen, and historical records, all pointing to the conclusion that people in the past have suffered through global warming periods before. So what happened?
Using data from truffle-hunting historians, Fagan told of how vineyard harvest records in Europe show that England became so warm during the period between 800-1250 AD that England not only had vineyards in its central provinces but it also exported wine to France. The medieval warm period had repercussions throughout society. Iceland and Scandinavia warmed up enough to grow cereal crops, tree lines elevated in mountain areas, and there were longer growing seasons everywhere on the continent.
This warming up of agriculture initiated the first vast clear-cutting of European forests. In the short 200 years between 1100 and 1300, from one-third to one-half of European wooded wilderness was deforested to make way for fields and pastures — shaping the lovely farm scenes we now associate with Europe. (Today only Poland has any remaining virgin forests).
Fagan says the myth of the medieval warm period is that it was warm. There was all kinds of weather extremes. In 1315 it started to rain for seven years. The newly cleared and naked hills eroded, dams burst, disease spread, and prolonged drought followed.And not just in Europe. Mesoamerica was jolted by long droughts. The Mayan pyramids at Tikal were engineered to act as water collection reservoirs. The collapse of their empire, and others in South America such as the Inca in Peru, are correlated to prolonged droughts.