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http://www.canada.com/calgaryherald/news/city/story.html?id=05ef3d95-e7e3-4861-b170-7fb2a0ef730c
Lessons from a thousand years ago
Reese Halter, Calgary Herald
Published: Sunday, May 11, 2008
My children often ask: Why is history so important? For which I regularly answer — because the past is rich with information and lessons.
From about AD 800 to 1300 the Earth underwent a slight warming period so dubbed “The Medieval Warm Period.” Most places experienced milder winters and longer summers but temperature differences never amounted to more than one degree C or so. And everywhere was not necessarily warmer. For example, the eastern Pacific was cooler and drier. Globally, the climate went through sudden and unpredictable swings. The most startling was the extent and duration of droughts. The difference between 20 millimetres of precipitation spells the difference between life and death.
During the Medieval Warm Period much of North America through to Central and South America, and across the Pacific to China, experienced long periods of severe aridity.
Without a doubt we know from tree rings, cherry blossom records dating back 1,000 years from Korea and Japan, western Pacific corals, seabed cores, ice cores from polar and subtropical mountain glaciers, and cores from alpine lakes that droughts were the lethal silent killer of the Medieval Warm Period.
Prolonged Medieval droughts decimated Chaco Canyon and the Pueblo Peoples of the American southwest and the Angkor Wat of India. Repeated drought cycles leveled the Mayans of Middle America, and starved tens of thousands of northern Chinese farmers.
Droughts also forced Mongolian horse nomads to search for new pasture and saw the rise in AD 1206 of Genghis Khan of one of the most ruthless and brutal warriors ever known on our planet.
Tree rings from cottonwoods and Jeffrey pines unearthed from a receding lake bed in east central California revealed intense droughts between AD 910 to 1100 and AD 1250 to 1350. The only way the Native Americans survived during these arid times was to co-operate and carefully manage their water supplies and food resources across the harsh landscape.
The endless debate over anthropogenic global warming is over, the voluminous scientific evidence detailing our contributions to today’s warmer world and of the future has well passed the phase of controversy.
Today, we are experiencing a sustained warming unknown since the end of the Pleistocene glaciation some 14,670 years ago.
The Quelcaya ice cap of southern Peru is retreating more than 60 metres a year, three times faster than in the 1960s. The Peruvian Andes have lost more than 21 per cent of their glacier area since 1970. At least 27 million people rely on the glaciers for their water supply.
The lessons from the warm centuries of a thousand years ago clearly show us that drought is a global problem. And the droughts of a warmer future will become prolonged and more intense.
Drought and water are the most important issues for this and future centuries.
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