Global warming and climate change arc established facts with thoughts arising on the fate of the planet in the next few decades. One approach is through the computer models used by the Intergovernmental Panel on Climate Change. Another is to consider how conditions changed in warmer historical periods, notably AD800-l300, the Medieval Warm Period. This book
THE GREAT WARMING: Climate Change and the Rise and Fall of Civilizations by Brian Fagan
is a sequel to another volume The Little Ice Age which covered the global cooling from about 1430 to 1850.
In Europe in the 12th and 13th centuries, England exported wine to France, and wine was also produced in southern Norway. The Norse settlement of Greenland in the
AD 980s, enjoyed a flourishing economy for three centuries until it was abandoned to the ice around 1450.
The Medieval Warm Period was not however a discrete episode when climate was distinctly different from what came before.
The collapse of the Classic Maya civilisation in Central America in the ninth century was probably precipitated by successive droughts in a land where water supplies were always under stress.
The settlement of remote Easter Island (Rapanui) around 1200 AD by canoeists heading east from Polynesia with westerly winds may have been made feasible by the faltering of the usual northeasterly Pacific trade winds during El Nino events connected with warmer sea-surface temperatures.
Genghis Khan’s Mongol invasion in the early 13th century could have been prompted partly by drought wreaking havoc on the pastures of the steppes. This possibility is supported by the withdrawal of his grandson Batu Khan and the Golden Horde in the 1240s at the height of their military success with the return of cooler, wetter conditions.
These suggestions are based on climatological studies of recent vintage, using ice-cores, deep-sea and lake cores, coral records and tree rings, and historical documents such as the reports of the flowering of cherry trees in Japan and Korea that date back a thousand years.
Five-hundred-year-old pines from the mountains of Mongolia have allowed experts to construct a climatic sequence back to AD 850. The prolonged warm period detected in the Mongolian tree rings coincides with Genghis Khan’s conquests, Tree rings from multiple western locations agree that the four driest periods centred on AD935, 1034, 1150 and 1253. followed by an extended wetter period from 1300-1900. then a return to droughts.
. Also important is the variation in solar irradiance caused by small tilts in earth’s orbit, sunspots and major volcanic eruptions the eruption of Mount Pinatubo in the Philippines in 1991, for example, counteracted current global warming for several years.
The medieval warming was generally good for Europe, but it produced prolonged droughts in many parts of the world, including the Sahara. Peru, India and northern China.
In a review of this book Robinson in the Financial Times Weekend Magazine March 15/16 2008 p 29 points out that the in the future the much larger human population, many living close to starvation, will be peculiarly susceptible to global warming.
- Martin Eastwood