Sir David Attenborough has warned that climate change is the greatest threat to humanity and could lead to the collapse of civilisations.

The stark message was issued to world leaders at United Nations climate talks in Katowice, Poland, who were urged to take action to drive down greenhouse gas emissions.

Sir David said the world was facing its "greatest threat in thousands of years” and that time was running out.

He warned: “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 world's people have spoken, their message is clear, time is running out, they want you, the decision-makers, to act now.

"They're supporting you in making tough decisions but they're also willing to make sacrifices in their daily lives."