The fate of civilisation itself lies squarely in the hands of today's leaders, Sir David Attenborough has warned in a strident address on behalf of the world's peoples.

Speaking at the opening of the United Nations COP24 Climate Change Conference in Katowice, Poland, Attenborough implored the assembled delegates and decision-makers to listen to the voices of those they represent – while there's still time to act.

"Right now, we are facing a man-made disaster of global scale. Our greatest threat in thousands of years," Attenborough said.

"If we don't take action, the collapse of our civilisations and the extinction of much of the natural world is on the horizon."

As part of COP24, Attenborough was speaking from the "People's Seat": an effort to give a voice to the billions of citizens who aren't in attendance at the UN summit – but whose continued existence on the planet depends on the decisions made over the next fortnight by the delegates invited.

As part of the initiative, people were asked to speak up on climate change using the hashtag #TakeYourSeat. At COP24, a video of these messages from citizens all around the world was played, describing their experiences and fears about climate change, and demanding world leaders take action to address the threat.

"The world's people have spoken. Their message is clear. Time is running out. They want you, the decision-makers, to act now," Attenborough said.

"Leaders of the world, you must lead. The continuation of our civilisations, and the natural world upon which we depend, is in your hands."

It was a message repeated by UN Secretary-General António Guterres at the opening, who told assembled leaders from over 150 countries that the world was not acting fast enough on efforts to curb greenhouse gas emissions, and urged them to finalise the implementation of the Paris Agreement in Katowice – with many countries already falling behind their pledges.

"It is plain we are way off course. We need more action and more ambition," Guterres said.

"We have no time for limitless negotiations… Let us rise to the challenge and finish the work the world demands of us."

It remains to be seen whether COP24 will provide the world-saving congress millions are hoping for, but with so much resting on how these talks play out, all eyes are on Katowice right now.