In the middle of the mighty Atlantic Ocean, the sky is beginning to darken. Hundreds of miles from the shore, a single boat is battling against the towering waves.

Inside the yacht, a huddled figure clings on in desperation. As the waves continue to pummelTo strike repeatedly. the tiny vessel, Greta Thunberg starts to sob: "It's too much for me."

This is a scene from "I am Greta", a documentary released last year, revealing the remarkable story of the teenage climate activist. It includes her epic carbon-neutralA project is carbon-neutral if it absorbs, locks in or converts as much carbon dioxide as it emits. journey across the Atlantic to a summit in New York.

In 2018, a 15-year-old girl from Sweden was refusing to go to school. Instead, she was sitting outside the country's parliament with a homemade sign and a simple message: "Skolstrejk for klimatetMeaning School strike for climate, now the watchword for an international movement of children who skip school on Fridays to protest about climate change.."

A few days later, filmmaker Nathan Grossman started filming. He did not bother to shoot in high definition: they would be lucky, he thought, if the grainy footage of a lonely teenager sitting on the grey streets of Stockholm, ignored by passersby, made it to the local news.

But within weeks, Thunberg had started a revolution. Arnold SchwarzeneggerAfter making his name as the star of films such as Terminator, he became a politician, serving as governor of California from 2003 to 2011. As of 2020, he is the most recent Republican governor of California. had retweeted her, and other children had joined her, with their own signs in their own languages. It was no longer a solitary child's campaign.

By September 2019, Greta was leading four million people in 150 countries for the Global Climate Strike, thought to be the biggest environmental protest in history.

And this week she mocked the words of world leaders in her speech at the Youth4Climate conference in Milan.

She used soundbites from Boris Johnson, such as "expensive bunny hugging" and "build back better", to highlight what she called the "empty words and promises" of politicians.

So what is so special about Greta Thunberg?

Thunberg herself believes that Asperger syndromeNow considered part of the autism spectrum, Asperger syndrome is named after Austrian paediatrician Hans Asperger who described some of its characteristics. They include difficulties with social interaction and non-verbal communication. plays a major part in her success. "I don't fall for lies as easily as regular people," she told the BBC last year.

Grossman's film casts a light on her authenticity: she is not driven by fame or popularity but because she feels she has no choice. "Once the climate crisis has got your attention, you can't look away," she explains.

Indeed, the documentary shows Greta at her highs, speaking in front of 30,000 at a UNUnited Nations. An intergovernmental organisation based in New York that aims to maintain international peace and security. conference - and at her lows, struggling to cope with the idea that her rising fame may be eclipsing her message.

Although Greta may be campaigning to save the world, she herself has already benefited from one aspect of her campaign. In the years before her school strike, she suffered from profound depression, at times refusing to eat or speak. Now, the campaign provides a goal for her "laser focus".

Indifferent to social pressures and norms, she has faced the ireAnger. Thunberg has been attacked by politicians and media figures. The American television network Fox News was forced to apologise after a guest called her a "mentally ill Swedish child". of world leaders with apparent ease: the Brazilian president Jair Bolsanaro called her a "brat" while Donald Trump suggested she had anger management issues.

Thunberg laughs off the criticism, but she does not respond to plaudits either. When an American congressmanThunberg told American Democrats: "I know you're trying... but just not hard enough. Sorry." hailed her "superpower", she replied: "Please save your praise. We don't want it. Don't invite us here to tell us how inspiring we are without doing anything about it."

No, say some. Charisma is based on self-belief, not authenticity. In today's celebrity culture, many of the people we admire are not that genuine at all. From the Kardashians to career politicians, most high-profile A-listers are self-manufactured creations. They present a highly curated image of themselves in the press or on social media, rather than their "real" or authentic selves.

Yes, say others. It is Greta's willingness to expose her vulnerabilities and tell the truth that makes her so powerful. The old idea of charisma, especially in politics, is based on smooth charm - but many now prefer brutal honesty. From Thunberg herself to the rise of populist politicians, who forgo conventions, it is clear that authenticity is indeed the secret of charisma.