The naturalist Sir David Attenborough has said climate change is humanity’s greatest threat in thousands of years.
The broadcaster said it could lead to the collapse of civilisations and the extinction of “much of the natural world”.
He was speaking at the opening ceremony of United Nations-sponsored climate talks in Katowice, Poland.
The meeting is the most critical on climate change since the 2015 Paris agreement.
Sir David said: “Right now, we are facing a man-made disaster of global scale. Our greatest threat in thousands of years. Climate change.
“If we don’t take action, the collapse of our civilisations and the extinction of much of the natural world is on the horizon.”
The naturalist is taking up the “People’s Seat” at the conference, called COP24. He is supposed to act as a link between the public and policy-makers at the meeting.
“The world’s people have spoken. Their message is clear. Time is running out. They want you, the decision-makers, to act now,” he said.
Speaking at the opening ceremony, Antonio Guterres, UN Secretary-General, said climate change was already “a matter of life and death” for many countries.
He explained that the world is “nowhere near where it needs to be” on the transition to a low-carbon economy.
But the UN Secretary-General said the conference was an effort to “right the ship” and he would convene a climate summit next year to discuss next steps.
Meanwhile, the World Bank has announced $200bn in funding over five years to support countries taking action against climate change.