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David Attenborough: 'The collapse of our civilizations is on the horizon'

(CNN)Renowned nature broadcaster David Attenborough has told world leaders that climate change could lead to collapse of civilizations, and much of the natural world.Speaking at the opening ceremony of the COP24 UN climate conference, in Katowice, Poland, Attenborough called climate change "our greatest threat in thousands of years."Follow the COP24 climate conference, liveIn the weeks leading up to the event, the UN asked people to send their thoughts on climate change. Attenborough was there to represent the public, by taking the "People's Seat" at the conference.He said: "The world's people have spoken. Their message is clear. Time is running out. They want you -- the decision makers -- to act now. "Leaders of the world you must lead," ...