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London's financial district, known as the Square Mile. Will it be one of the first dominoes to fall when society can no longer sustain itself? Peter Macdiarmid/Getty Images hide caption

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Peter Macdiarmid/Getty Images

An urban farmer waters his plants near Bamako, Mali, where the government has set aside nearly 250 acres for market gardens. donkeycart/Flickr hide caption

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donkeycart/Flickr