The Swedish climate activist Greta Thunberg has become known globally for her environmental campaign. In August 2018, aged 15, Thunberg began a solo climate protest by striking from school. She has since been joined by tens of thousands of school and university students in more than a dozen countries, in climate strikes that have become regular events. A global strike in March drew more than a million people, surpassed in September by the biggest yet with at least 4 million.

Thunberg has described the rapid spread of the strikes around the world as amazing. “It proves you are never too small to make a difference,” she said. Her protests were inspired by US students who staged walkouts to demand better gun controls in response to multiple school shootings.

Veteran climate activists have expressed surprise at how much impact Thunberg has had on public awareness in such a short time.

Thunberg has begun travelling to spread her message outside Sweden. Speaking at the United Nations climate conference in December 2018, she berated world leaders for behaving like irresponsible children. And in January 2019 she rounded on the global business elite in Davos: “Some people, some companies, some decision-makers in particular, have known exactly what priceless values they have been sacrificing to continue making unimaginable amounts of money. And I think many of you here today belong to that group of people.”

Facebook Twitter Pinterest Greta Thunberg during the 20 September climate strike in New York. Photograph: Eduardo Muñoz/AP

Born in Stockholm in January 2003, her mother is Malena Ernman, who gave up her international career as an opera singer because of the climate effects of aviation. Her father, Svante Thunberg, is an actor. Greta has Asperger syndrome, which has, her father says, in the past affected her health. She sees her condition not as a disability but as a gift that has helped open her eyes to the climate crisis.

She has attracted criticism, particularly from rightwing commentators, who claim she is too young or naive to know what she is talking about and is being manipulated by her parents. One commentator on Fox News referred to her as a “mentally ill Swedish child”, for which the network was forced to apologise. She has rebutted these criticisms and shown that she can live her low-carbon values with a vegan diet and by sailing to New York, rather than flying.

Thunberg has insisted she is just relying on the science. Rather than submitting prepared remarks before an appearance at the US Congress, she submitted a landmark IPCC climate report that warned of the rapidly approaching catastrophe of global heating, asking them to read it. She says: “I think that as long as they go after me personally with insults and conspiracy theories then that is good. It proves that they don’t have any arguments. And that they see us as a threat because we are having an impact.”

In September 2019 she condemned world leaders in an emotional speech at the UN, telling them: “You have stolen my dreams and my childhood with your empty words.”

Play Video 4:34 Greta Thunberg to world leaders: 'How dare you – you have stolen my dreams and my childhood' - video

One one occasion she crossed paths with the US president, Donald Trump. Her glare became a social media viral sensation. He tweeted mockingly: “She seems like a very happy young girl looking forward to a bright and wonderful future.” Thunberg turned around the jibe by adopting it as her Twitter bio.

Regarding her early start to activism, she told Guardian readers: “I don’t care about age. Nor do I care about those who do not accept the science. I don’t have as much experience, and therefore I listen more. But I also have the right to express my opinion, no matter my age. Being young is a great advantage, since we see the world from a new perspective and we are not afraid to make radical changes.”