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Greta Thunberg has thanked broadcaster Sir David Attenborough for helping to inspire her into climate activism as the pair met for the first time over Skype.

The Swedish 16-year-old said that watching documentaries about the natural world when she was younger "opened her eyes" to what was happening with the environment.

Greta, who was guest editor of BBC Radio 4's Today programme on Monday where she chatted to Sir David on Skype, said: "Thank you for that because that was what made me decide to do something about it."

Sir David, 93, described the impact she has made as "astonishing," adding: "She has achieved things that many of us who have been working on it for 20-odd years have failed to achieve and that is you have aroused the world."

Greta started a school "strike for the climate" outside the Swedish parliament in August 2018, which has since spread all over the world to involve more than 100,000 schoolchildren.

The teenager's campaigning message that the world belongs to young people is "a very powerful one," according to Sir David, who told the youngster: "You have made it an argument that people have not been able to dodge."

He told Greta: "We don't want to spend our time marching through the streets but we have to. People of my generation should be very grateful to you."

Greta was nominated for this year's Nobel Peace Prize after spearheading a global movement demanding world leaders take action on climate change.

She is currently on a gap year from her education and heads back to school in August.

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She has suffered with depression and feels her activism has been like a medicine.

She told Radio 4: "It really helps in getting out of that depression because it gives a feeling you are having an impact."

Greta added: "Just being part of a movement that has so much impact on the world is an amazing feeling. I wish that more people could feel like that."

Brazil's president Jair Bolsonaro has called her a "brat" after she condemned violence against indigenous people who were killed in the Amazon, while US President Donald Trump has suggested she has anger management issues.

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She said she thought those attacks were "just funny", and were probably because she was part of a big movement they probably see as "a threat".

Greta, who was seen glaring from a distance at Mr Trump in the lobby at the United Nations in New York earlier this year, said that talking to him would have been a waste of time.

She said: "He is obviously not listening to scientists and experts. Why would he listen to me?

"So I probably wouldn't have said anything. I wouldn't have wasted my time."

Greta said she feels climate activists are being listened to, although the science is being ignored by people in politics, finance and the media.

She said she is going into the new year feeling "realistic", adding: "It is not like it is going to change overnight."