The nations granddad 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.
The UK government has published an overview of the legal advice it received on Theresa May’s Brexit deal.
Ministers are under pressure from all parties to publish the full advice, with Labour warning of a “constitutional crisis”.
The PM says the advice is confidential, but some MPs think ministers do not want to admit it says the UK could be indefinitely tied to EU customs rules.
Attorney General Geoffrey Cox will make a statement about it later.
Sam Gyimah, who quit the government on Friday, said releasing the full advice was “key to restoring trust in politics”.
MPs say this will not not respect a binding Commons vote last month, which required the government to lay before Parliament “any legal advice in full”.
Mark Hughes has been sacked as Southampton manager after eight months in charge.
The Saints, who drew with Manchester United in the Premier League on Saturday, are 18th in the table.
Southampton confirmed the move in a statement, adding: “The search for a new manager to take the club forward is already under way.”
First-team assistant coach Kelvin Davis will take charge of the team for the game against Tottenham on Wednesday.
BBC Sport understands Southampton are set to approach former RB Leipzig manager Ralph Hasenhuttl about the manager’s job. The 51-year-old Austrian has been out of work since leaving Leipzig in May.
Hughes, who also had a spell at the south coast club during his playing career, joined Southampton in March, two months after being sacked by Stoke City
The club were one point above the relegation zone at the time and the 55-year-old led them to safety last season by securing two wins from their last four games.
However, they have struggled again this season and, across his spell, have won just three of their 22 league games.
Before the draw against Manchester United, Southampton were beaten 3-2 by relegation rivals Fulham and knocked out of the EFL Cup on penalties by Leicester.
Along with Hughes, assistant first-team manager Mark Bowen and coach Eddie Niedzwiecki have also left the club.