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Sir David was named a champion of the Earth by the UN.
The 95-year-old was awarded the prestigious award for his commitment to telling stories about the natural world and climate change.
Sir David said the world must protect nature and the planet.
The Green Planet and A Plastic Ocean were his celebrated documentaries.
Sir David said that environmental success stories should give us hope.
Fifty years ago, whales were on the verge of extinction. He suggested that there are more whales in the sea than any living human has ever seen.
We know how to solve the problems. Unified action is all we lack.
UNEP Executive Director Inger Anderson said that Sir David was recognised by the UN because of his dedication to broadcasting the natural world.
Inger Andersen, UNEP Executive said that if we stand a chance of averting climate and biodiversity breakdowns and cleaning up polluted ecosystems, it is because millions of us fell in love with the planet that he captured on film and writing.
In the 1950s, Sir David began working on natural history programmes, and his programmes filmed in far- flung parts of the world became immensely popular. In the past four years, his warnings about the damage that climate change is causing the planet and humans have become more stark.
Sir David is popular with children and teenagers who are worried about climate change. Teenage climate activist Greta Thunberg has said that meeting the broadcaster was awe-inspiring and that everyone should strive to be like him.
Children visiting the London aquarium told the news organization they love watching Sir David on TV and have books about him.
He supports our planet and the animals. He tells us on his show that the natural world might be in danger if we don't make a difference.
She thinks we should stop using plastic, use more electric cars, and plant more trees to save the planet.
Benjamin said he was inspired to become a marine biologist by watching Sir David. They taught him about the dangers of climate change.
I want to be able to have a family and I want them to live in a nice world. If we start trying very hard, we can save the natural world.
Prof Rick Stafford, a marine biologist at Bournemouth university, told the BBC that Sir David's emphasis on success stories like bringing back whales from the point of extinction is important.
He brought climate change and biodiversity loss to the forefront. The major problems to be solved are not scientific, but economic and political.