Megadroughts could trigger medieval-style collapse

The civilization of Angkor in the Khmer Empire, which flourished from the 9th to the 15th century in what is now Cambodia, rivalled the greatest civilizations on Earth. The Khmers created a medieval megacity boasting an intricate system of canals and awesome temples of stone and religious monuments, which still astonish tourists from around the world.

Then within a few generation Angkor collapsed, forcing most of its inhabitants to relocate elsewhere. The reason included prolonged droughts and devastating floods that in turns desiccated crops and destroyed irrigation canals. Where once a great civilization thrived, only dilapidated temples and ruins of stone would remain.

Halfway across the world a similar scenario played out right about the same time. Prolonged megadroughts helped cause several flourishing indigenous civilizations to collapse in the southwest of what is now the United States.

The same could happen to today’s cities and communities in these areas and elsewhere. So says a team of scientists in the U.S., who reconstructed climatic and aquatic data worldwide while examining sea-surface temperatures over the past two millennia. They have pinpointed 14 droughts that lasted more than a decade, all of them before the start of the 17th century.

Three key factors were noticeable in each medieval megadrought, they say. The planet’s surface began to absorb more energy from the sun, which caused the North Atlantic Ocean’s surface to warm. That in turn worsened destructive La Niña events. The results included seemingly endless droughts, devastating floods and more frequent storms. Combined, these extreme weather events dealt a blow to the ways of life in people in certain areas.

That was then, but it could happen today too, the scientists warn. As a result of our wanton global CO2 emissions, which create a greenhouse effect that traps more heat from the sun on the planet’s surface, medieval-style megadroughts could soon return.

“Eighty percent or more of the water used by the American West is used for agriculture,” says Nathan Steiger, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory who is the lead author of a new study published in the journal Science. “A megadrought could fundamentally change how communities are supported, how farmers in the West and California in particular do work, what they plant, if farming is even possible or not.”