Thunberg's meteoric rise to world fame was punctuated in November when she spoke before the United Nations Climate Action Summit.
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Since 2018 she has been a symbol for youth across the world demanding more action to address climate change.
The young activist turned heads last December when she traveled to Katowice, Poland, for the two-week talks at the U.N. world climate conference. She sailed for three weeks across the Atlantic to attend this year's climate summit in Lisbon, Portugal, which was held last week.
» RELATED: Greta Thunberg arrives by sail in Europe for climate talks
Time made its announcement Wednesday morning on the “TODAY” show and on Twitter.
The magazine annually names a person or persons who “most influenced the news and the world” during the past year.
This year's finalists for the honor included President Donald Trump, Speaker of the House Nancy Pelosi, the anonymous whistleblower whose complaint led to the impeachment inquiry.
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On its website, Time said it chose Thunberg "for sounding the alarm about humanity’s predatory relationship with the only home we have, for bringing to a fragmented world a voice that transcends backgrounds and borders, for showing us all what it might look like when a new generation leads."
"She became the biggest voice on the biggest issue facing the planet this year, coming from essentially nowhere to lead a worldwide movement," Time editor-in-chief Edward Felsenthal told "TODAY."
» MORE: Greta Thunberg's North Dakota photo is at national library
Thunberg’s sudden celebrity has not been without controversy.
In September, President Donald Trump was accused of mocking the teen on Twitter after she called out world leaders for not doing enough to tackle the climate crisis.
"She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!" Trump posted on Twitter, replying to a video of Thunberg's speech at the United Nations climate action summit earlier in the day.
The next day, Thunberg updated her Twitter bio to read: "A very happy young girl looking forward to a bright and wonderful future."
Other world leaders are also finding themselves caught up in the "Greta Thunberg effect" — a term some media have used describe the teen's impact on the world stage.
» RELATED: Brazil's Bolsonaro calls activist Greta Thunberg a “brat”
Just on Tuesday, Brazil's president called Thunberg a "brat" after she condemned the killings of indigenous people in the Amazon.
"Greta has said that the Indians died because because they were defending the Amazon. It's amazing that the press gives space to this kind of pirralha," Jair Bolsonaro told reporters, using the Portuguese word for "brat."
Thunberg also appeared on the cover of Time in May. That issue called her a "next generation leader."
She was also a nominee for the 2019 Nobel Peace Prize, which ultimately was awarded to Ethiopian Prime Minister Abiy Ahmed Ali.
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