She has sparked both hope and controversy around the planet, but Greta Thunberg understood climate change at an early age and has rallied youths and parents worldwide to her cause.

In just over a year the now 16-year-old Swede’s humble “climate strike” has become a global movement and set her up as a potential 2019 Nobel Peace Prize laureate.

Thunberg’s struggle began quietly in August 2018 when she skipped school for the first three weeks, and then on Fridays to spend the day outside Sweden’s parliament with a sign labelled “School strike for climate”.

Swedish media, at the time preoccupied by upcoming parliamentary elections, didn’t pay much attention to the young girl’s message at first.

Most often seen wearing her hair in tightly knit braids, Greta diligently pursued her weekly sit-in even as temperatures plunged.

“I’m planning to continue until Sweden is in line with the Paris agreement and that might take a while,” she told AFP TV in late 2018.

Her demands have attracted worldwide attention -- she has been asked to address global leaders and adorned the cover of international magazines such as Time and Vogue.

Earlier this week, Greta and her Fridays for Future movement received Amnesty International’s highest human rights award.

In August, she crossed the Atlantic to New York in a two-week journey on a sailboat. She refuses to fly because of the carbon emissions caused by airplanes.

Around the world, young activists have heeded the call and modelled protests of their own after Greta’s, leading to both praise and criticism.

On Wednesday in Washington, she addressed a joint hearing of two House committees.

“I don’t want you to listen to me, I want you to listen to the scientists,” she said. “I want you to then unite behind the science -- and then I want you to take real action.”

It was in school, when Greta Thunberg was eight or nine, that her interest in climate issues was first piqued.

“My teachers told me that I should save paper and turn off the lights. I asked them why and they said because there’s something called climate change and global warming, caused by humans,” Greta told AFP.

The notion was strange to the young girl, who felt that if that was the case, “then we would not be talking about anything else”.

Since then she has stopped eating meat, drinking milk and buying new things, unless “absolutely necessary”.

Greta’s family, who live in a spacious but cosy Stockholm apartment, has also made changes to their lifestyle.

As an opera singer, her mother Malena Ernman used to travel the world, but she has bowed to her daughter and now performs only in Nordic countries.

Her mother, father Svante Thunberg, an actor turned producer, and younger sister Beata became aware of how much the troubled climate weighed on Greta’s shoulders when she became depressed.

At age 11 Greta stopped eating, started missing school and even stopped talking as the “existential threat” of climate change loomed, her father said.

When she was 12, Greta was diagnosed with Asperger’s syndrome, a mild form of autism.

“My brain works a bit differently so I see the world from a different perspective,” Greta explained to AFP.

“I am very direct, I say it the way it is, and when I decide to do something, I do it without doubt,” she said, adding that she considers her condition a strength.

Greta has taken a sabbatical from school this year after graduating from ninth grade in June with mostly A’s.

“We have to take the opportunity to act now because it may be too late in just a year,” she warned in December.