Sir David Attenborough 'delivers greatest message ever' as he prepares to turn 99

says he is sharing of his career The beloved wildlife expert will mark his landmark birthday on Thursday, having .

He is also gearing up for the release of his cinema-length film Ocean, which and protecting the planet from climate change.

Sir David said: "After almost 100 years on the planet, I now understand the most important place on Earth is not on land, but at sea."

The film argues how the ocean is the planet's support system and our greatest ally against climate disaster. It is also set to show how all the world's oceans are at a crossroads.

Ocean will premiere later today at Royal Festival Hall, with a blue carpet rolled out for the occasion. An array of celebrities are set to be in attendance, including Coldplay's Chris Martin, actor Benedict Cumberbatch, astronaut Tim Peake and Spice Girl Geri Halliwell-Horner.

The film documents how the oceans and our understanding of them has changed over Sir David's life. Producer Toby Nowlan said: "This is not about seeing brand new natural history behaviours. It is the greatest message he's ever told."

Sir David takes viewers back to his first scuba dive in 1957 on the Great Barrier Reef. He said: "I was so taken aback by the spectacle before me I forgot – momentarily – to breathe."

Devastatingly, there has been a catastrophic decline in life with the broadcasting veteran noting: "We are almost out of time." Sir David even revealed the state of the ocean almost made him lose hope for future life on our planet.

However, what has kept him from his despair has been the "most remarkable discovery of all" that the ocean can "recover faster than we had ever imagined".

The key message in his film is that all is not lost, as he hopes it will spur leaders to take action. "The ocean can bounce back to life," Sir David said. "If left alone it may not just recover but thrive beyond anything anyone alive has ever seen."

Last week, the broadcaster expressed that he is "nearing the end of his life." He referred to his own mortality while discussing his upcoming series for Disney+.

"When I first saw the sea as a young boy, it was thought of as a vast wilderness to be tamed and mastered for the benefit of humanity. Now, as I approach the end of my life, we know the opposite is true," he said.

"After living for nearly a hundred years on this planet, I now understand that the most important place on Earth is not on land, but at sea."

Through his documentaries, Sir David has long highlighted the environmental challenges facing the and contributed to the development of initiatives aimed at protecting endangered species.

The 98 year old broadcaster shared: "The world would be in a far, far worse situation now had there been no broadcasting of natural history. People have found it a source of fascination, beauty, and interest, which has become key to looking after the world."

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