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archaeology was the sudden collapse of the Mayan Civilisation of Central America. The disappearance of one of the great civilisations of the ancient world puzzled scientists for years, as they searched for clues among the ruined and deserted Mayan cities. How could a sophisticated culture with its knowledge of mathematics and astronomy vanish into thin air? At its height in about 800 AD, there were probably about 13 million •Mayans supporting elaborate cities with grand pyrarnid temples. Their lands extended from Chichen Itza on Mexico's Yucatan Peninsula, through Tikal in Guatemala to Copan in Honduras. And then, almost instantly, everything collapsed. Researchers have recently discovered that it was in fact climate change that caused the collapse of Mayan culture. It coincides directly with several periods of intense drought each lasting about a decade. The worst drought lasted between about 760 and 800 AD. Each one put more intense pressure on an already fragile civilisation. The cities were densely populated. But they relied on corn-growing farmers who didn't produce enough to sustain both themselves and the city dwellers. Even though the Maya built reservoirs to collect water, their crops still depended on seasonal rains. Their land had few rivers, being mostly dry limestone. When the rains failed, the water for drinking and agriculture simply ran out. With few reserves and lacking what became crucial for survival, Mayan Civilisation died. History has many examples of cultures that collapsed in other parts of the world. Almost 3,500 years ago, a drought lasting about 200 years terminated a flourishing society in Mesopotamia. Scientists know from studying the rings in trees that a drought in about 1130 AD destroyed the Anasazi culture of the Chaco Canyon in New Mexico, USA. But not all societies have had to surrender to the devastating effects of drought. The Chumash, of California's Channel Islands, apparently changed their behaviour in response to climate change. When deadly droughts threatened their survival, these hunter-gatherers became traders. What can modern societies learn from the Maya's downfall? Supplies of clean water are one of the biggest problems facing countries all over the world. Australia has experienced record droughts since the start of the 21st century. The western USA uses so much water that the Colorado River is dry by the time it joins the sea. People will have to change their habits even more, in order to survive the climate changes that are predicted in the next decades.