Swedish climate change activist Greta Thunberg warned world leaders at the Davos World Economic Forum that "they haven't seen anything yet."

"We are now in a new year, and we have entered a new decade. And so far, during this decade, we have seen no signs whatsoever that real climate action is coming. And that has to change," Thunberg said.

Thunberg, 17, is in her 74th week of protesting climate change as part of her Fridays for Future campaign. The teenager finished second in Nobel Peace Prize voting for 2019 and stared down President Trump at a United Nations meeting on religious freedom in September. Trump told Thunberg to "chill" and go see a movie with friends.

"We need to make clear that this is just the beginning!" Thunberg said. "To the world leaders, and those in power, I would like to say that you haven't seen anything yet. You have not seen the last of us, we can assure you that."

Thunberg apologized in December after saying world leaders should but put "up against the wall" if they did not act on climate change. Her father, Svante Thunberg, said the teenager "didn't eat for three months" while experiencing depression a year before beginning her climate strike outside the Swedish Parliament.

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