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.
What’s so different about this meeting?
This Conference of the Parties (COP) is the first to be held since the landmark Intergovernmental Panel on Climate Change (IPCC) report on limiting global temperature rise to 1.5C came out in October.
The IPCC stated that to keep to the 1.5C goal, governments would have to slash emissions of greenhouse gases by 45% by 2030.
But a recent study showed that CO2 emissions are on the rise again after stalling for four years.
In an unprecedented move, four former UN climate talks presidents issued a statement on Sunday, calling for urgent action.
They say “decisive action in the next two years will be crucial”.
Meanwhile, the gap between what countries say they are doing and what needs to be done has never been wider.
So urgent is the task that some negotiators began their meetings on Sunday, a day before the official start.
Will global leaders be attending?
Yes, some 29 heads of state and government are due to give statements at the opening of the meeting.
The number is way down on the stellar cast that turned up in Paris in 2015, which perhaps indicates that many are seeing this as more a technical stage on the road to tackling climate change than a big bang moment.
But for the likes of China and the EU, the meeting is critical. They will want to show that international co-operation can still work even in the age of President Trump.