Greta Thunberg has been named Time's 2019 Person of the Year, becoming the youngest ever recipient of the title.
The activist, 16, inspired the school strikes for the climate movement.
She has become the face of the youth climate movement, drawing large crowds with her appearances at protests and conferences over the past year and a half.
Veteran campaigners and scientists have welcomed her activism, including her combative speeches challenging world leaders to do more to stop global warming.
Time editor-in-chief Edward Felsenthal told the Today show: 'She became the biggest voice on the biggest issue facing the planet this year, coming from essentially nowhere to lead a worldwide movement.'
He confirmed she is the magazine's youngest ever choice. Malala Yousafzai was runner up in 2012, losing out to Barack Obama, aged 15.
Thunberg's angry accusations that world leaders are failing the younger generation have made headlines, including her shouts of 'How dare you?' at the U.N. General Assembly earlier this year.
An image of her stare at Donald Trump as he entered the UN quickly became a social media meme.
Politicians have, by and large, praised Thunberg, who has Asperger's syndrome, and her movement as an important voice of her generation.
Former Vice President Al Gore said Wednesday: 'Brilliant decision for @TIME to choose @GretaThunberg as its Person of the Year.
'Greta embodies the moral authority of the youth activist movement demanding that we act immediately to solve the climate crisis. She is an inspiration to me and to people across the world.'
Thunberg was in Madrid on Wednesday, where she addressed negotiators at the U.N.’s COP25 climate talks.
There she accused political and business leaders of polishing their images rather than taking aggressive action in the fight against climate change at the UN climate talks.
In a speech given at the COP25 talks in Madrid, Spain, the teenager also criticized governments for avoiding taking action to cut greenhouse gas emissions and 'not behaving as if we are in an emergency'.
Greta, who inspired the school strikes for the climate movement, said: 'The biggest danger is not inaction; the real danger is when politicians and CEOs are making it look like real action is happening, when in fact almost nothing is being done apart from clever accounting and creative PR.'
She said the science showed that, at the current rate of emissions, the world is set to use up the whole 'carbon budget' - the amount of pollution that can be put into the atmosphere and still keep global warming to 1.5C - in eight years.