Sir David is filming for a BBC 1 series, Frozen Planet
Sir David Attenborough has realised a life-long ambition and reached the North Pole, the BBC has said.
The broadcaster, 84, is filming in the Arctic Circle for Frozen Planet, a BBC One series due to air in late 2011.
Sir David, who has also visited the South Pole for the series, said it was a "huge privilege" to reach both Poles.
The BBC said the seven-part series is the "ultimate polar expedition to the last great wilderness on the planet - before the regions change forever".
Speaking from the Svalbard archipelago, 700 miles from the North Pole, Sir David said: "The Poles - North and South - look superficially very similar.
"But when you visit them within a few weeks of one another, as I have just done, you realise how profoundly different they are and how what is happening to them is going to affect the entire planet."
He said a century ago the Poles "were just about the most inaccessible place on earth" but times had changed.
"Nonetheless, to have visited them both within a few weeks of one another is a huge privilege.
"Most of the programmes I have made over the past 50-odd years have been about the tropical parts of the world.
"Having seen what I've just seen - from penguins to polar bears, from the frozen ocean to snow-covered volcanoes - I can't imagine why I've left visiting these marvellous, astonishing and beautiful places until so late in my life," he said.
The wildlife presenter will also author the final episode, Meltdown, an environmental special in which he looks at what the future might hold for the animals and people who live at the Poles - and what the effects of climate change there might mean for everyone else.