And these upheavals are leading to mass migrations, migrations of people.

这些急剧兴盛带来了大移民，人口的大迁徙。

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Past mass migrations were sparked by geopolitical circumstances rather than natural disasters, O'Neil said.

CNN: STORY HIGHLIGHTS

From pharaohs to the medieval Vikings, swift and sometimes violent changes in weather patterns sparked mass migrations and technological innovations like irrigation.

CNN: Past may hold clues to climate's future

It also highlights the consequences of climate-related mass migrations.

BBC: Climate 'biggest health threat'