In 2006, the British economist Nicholas Stern warned that one of the biggest dangers of climate change would be mass migration. "Climate-related shocks have sparked violent conflict in the past," he wrote, "and conflict is a serious risk in areas such as West Africa, the Nile Basin, and Central Asia."

More than a decade later we're still trying to create models that might tell us where people might move, and when. Last year a report for the World Bank, the first to model migration due to climate change on a large scale, estimated that as many as 143 million people in sub-Saharan Africa, South Asia, and Latin America could have to relocate within their countries by 2050.

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