Sir David Attenborough has said he cheered when he found out US President-elect Joe Biden plans to rejoin the Paris Agreement on climate change.
The broadcaster, 94, said the world is facing a “real crisis” that could see the majority of the planet’s major cities plunged beneath the oceans.
He was speaking ahead of the launch of A Perfect Planet, a natural history series he has presented for BBC One.
Discussing the moment when it became clear Mr Biden was to win the presidency and rejoin the Paris Agreement, Sir David said: “I can’t remember actually getting out of my seat and cheering all by myself until that moment.
“I mean, I’ve never done it before, even on our own elections.”
Under the Paris Agreement, countries have committed to keep global warming to below 2C above pre-industrial levels, and pursue efforts to limit it to 1.5C, seen as the threshold beyond which the worst impacts of climate change will be felt.
Sir David, who has frequently spoken out on environmental issues, added: “We are facing a real crisis and it’s not just talk.
“If we warm the Earth to such a degree that the Arctic melts, every city in the world – every big city in the world, very nearly, will be underwater.
“A high proportion of the important cities in the world are built around the coast because of their ports and… if the northern Arctic melts, the seas are going to rise and flood those cities.
“That’s not imagination, that’s not HG Wells, it’s not science fiction, it’s going to happen and we have still got a chance to stop it happening.”
Sir David said that when he was flying over Miami in a helicopter while filming a series he asked the pilot about the prospect of the city being submerged under water and he responded to say that he was talking “rubbish”.
“He didn’t believe it. He sees no reason why anybody should take any action and you have to say there’s a very strong element in the United States that does not believe it – including the past president.”
Next month a new natural history series presented by Sir David will air on BBC One.
A Perfect Planet will explore the impact of natural phenomena such as sunlight, volcanoes, weather and oceans on Earth.
The series will also explore humans’ impact on the planet.
A Perfect Planet airs on January 3 at 8pm on BBC One.