Greta Thunberg, the Swedish schoolgirl who inspired a global movement to fight climate change, has been named Time magazine's Person of the Year for 2019.
The 16-year-old is the youngest person to be chosen by the magazine in a tradition that started in 1927.
Shortly before the announcement, she told a UN climate change summit in Madrid that the next decade would define the planet's future.
She urged world leaders to stop using "creative PR" to avoid real action.
Last year, the teenager started an environmental protest outside the Swedish parliament building, sparking a worldwide movement that became popular with the hashtag #FridaysForFuture.
Since then, she has become a strong voice against climate change and an internationally recognised figure and, earlier this year, was nominated as a candidate for the Nobel Peace Prize.
Announcing Time's decision on NBC, editor-in-chief Edward Felsenthal said: "She became the biggest voice on the biggest issue facing the planet this year, coming from essentially nowhere to lead a worldwide movement."
The magazine's tradition, which started as Man of the Year, recognises the person who "for better or for worse... has done the most to influence the events of the year". Last year, it named killed and imprisoned journalists, calling them "The Guardians".
What happened in Madrid?
At the COP25 Climate Conference in Madrid, Greta Thunberg accused world powers of making constant attempts to find loopholes to avoid making substantial changes.
"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, drawing applause.
Summits on climate change seemed "to have turned into some kind of opportunity for countries to negotiate loopholes and to avoid raising their ambition", she added.
The clock was ticking as the decade comes to a close, she said. "In just three weeks we will enter a new decade, a decade that will define our future. Right now, we are desperate for any sign of hope."
A speech grounded in research
This was meant to be a big moment in the talks, the elixir of the "Greta effect" bringing new energy to a flagging process. The teenager is almost certainly the most famous person here, attracting far more attention than other celebrities like Al Gore, and the UN badly needs a boost.
Her talk came over as measured, grounded in the latest research, and avoided the flash of hurt and anger she displayed in New York in September. Looking around the hall, it was striking how many of the national delegations had not turned up for this morning session at the conference.
A snub by the big fossil fuel economies? Or maybe they were too busy in the negotiations themselves?
In any event, the passion among the millions of young people who have taken to the streets to demand action on climate change feels very remote from the diplomatic struggles in these halls.
The activist's speech came after Brazil's far-right President Jair Bolsonaro lashed out at her after she expressed concern about the killing of indigenous Brazilians in the Amazon.
"Greta said that the Indians died because they were defending the Amazon," Mr Bolsonaro told reporters.
"It's impressive that the press is giving space to a brat like that," he added, using the Portuguese word for brat "pirralha".
The activist responded by changing her Twitter bio to Pirralha.