Climate campaigners Greta Thunberg and Sir David Attenborough have joined forces to push politicians and businesses to step up action on climate change after a year in which schoolchildren took to the world's streets in protest.

Key points: Both Ms Thunberg and Sir David called on politicians to ensure next year's UN climate talks in Scotland produce a successful outcome

Both Ms Thunberg and Sir David called on politicians to ensure next year's UN climate talks in Scotland produce a successful outcome Ms Thunberg has transformed over the past year from an unknown, solo campaigner to the figurehead of a global movement

Ms Thunberg has transformed over the past year from an unknown, solo campaigner to the figurehead of a global movement Ms Thunberg's father explained how he and his wife had changed their lives as their daughter found out about climate science

Swedish teen activist Ms Thunberg, who turns 17 this week, said 2019 had been "a very strange year" as millions of young people skipped school to demonstrate over slow progress on tackling climate change, inspired by her weekly vigils at the Swedish parliament.

British naturalist and broadcaster Sir David, 93, said Ms Thunberg had "aroused the world" about the urgency of reining in global warming, achieving things that people who had worked on the problem for 20-odd years had not.

Sir David — famous for his TV series showing the impact of environmental degradation on flora and fauna — said he had flagged the need for changes to political structures and daily lives two decades ago, but "no-one took a blind bit of notice".

Ms Thunberg urged people to "read up" about climate science and what is being done — or not — to tackle the problem.

Large crowds marched in Sydney and around the world as part of a movement inspired by Greta Thunberg. ( ABC News: Brendan Esposito )

"We climate activists are being listened to — but that doesn't mean that what we are saying is translated into action," she told BBC Radio 4's Today show on which she was guest editor.

"It needs to be a big shift, and that's what we are waiting for — this tipping point," said Ms Thunberg who has Asperger's syndrome and has also suffered from depression in the past.

Sir David said it was depressing when governments in the United States, Brazil or Australia indicated they were not taking any notice of what should be done.

"It needs a real electric shock — such as you have produced socially — to bring them to their senses, and let's hope that shock will go on," Sir David told Ms Thunberg on the Today show.

Sir David Attenborough said he had attempted to stress the urgency of climate action two decades ago. ( Supplied )

Ms Thunberg has transformed over the past year from an unknown, solo campaigner to the figurehead of a global movement, winning a list of accolades and awards along the way including being named Time Magazine's Person of the Year for 2019 for her work.

In another interview with the BBC, her father Svante explained how he and his wife had changed their lives as their daughter found out about climate science.

He said Greta did not eat for three months, nor speak to people outside her family at one stage, but becoming a climate activist had enabled her to recover and become a happy teenager who "dances around" and "laughs a lot".

The family has since become vegan and no longer uses planes, instead sailing across the Atlantic this year to attend a UN climate action summit in New York and then sailing to Spain for December's global climate talks in Madrid.

"I didn't do it to save the climate, I did it to save my child," said her father.

Both Ms Thunberg and Sir David called on politicians to ensure next year's UN climate talks in Scotland produce a successful outcome, with governments due to strengthen their national plans to combat climate change.

The annual conference in Madrid this month was viewed as disappointing, with large carbon-polluting countries resisting pressure to step up their targets to reduce emissions.

"We, and they, must do everything they can to make sure that it doesn't fail and that we succeed in bringing the science into the conversation," Ms Thunberg said.

Reuters