More than half of the world's food comes from rain-fed farms, as opposed to irrigated ones.

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Of course, rain-fed agriculture is even more vulnerable to climate change than the irrigated variety, as Ms Parcak's Cambridge colleague Lauren Ristvet showed the conference with her study of northern Syria during the same period as the fall of Egypt's Old Kingdom.

ECONOMIST: Climate change and civilisation

Partly as a result, the land irrigated by canals has decreased by 35% since 1990.

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Weiss is dusting off evidence in the region known as the Fertile Crescent, including much of modern-day Iraq and Syria, indicating that a human revolution in irrigated agriculture occurred after an extended drought and cold spell.

CNN: Past may hold clues to climate's future