Teen environmental activist Greta Thunberg delivered an emotional and scathing speech at the United Nations on Monday, accusing world leaders of stealing her dreams and her childhood with their inaction on climate change.

"I shouldn't be up here. I should be back at school on the other side of the ocean," the 16-year-old from Sweden told the United Nations Climate Action Summit. "Yet you all come to us young people for hope. How dare you! You have stolen my dreams and my childhood with your empty words."

Thunberg slammed the members of the U.N. for caring more about money and "fairytales of eternal economic growth" than collapsing ecosystems, mass extinctions and people suffering due to climate change.

"You say you hear us and that you understand the urgency, but no matter how sad and angry I am I do not want to believe that because if you really understood the situation and still kept on failing to act, then you would be evil, and that I refuse to believe," Thunberg said.

She also said that the "popular idea" of cutting emissions by 50 percent in 10 years only yields a 50 percent chance of keeping the earth's warming trend below the 1.5 degree Celsius threshold, which could set off "catastrophic chain reactions beyond human control" if breached.

"A 50 percent risk is simply not acceptable to us — we who have to live with the consequences," she said.

Thunberg said the earth’s remaining CO2 budget was rapidly dwindling — citing a report from the Intergovernmental Panel on Climate Change that said the planet has experienced a more than 70 gigaton deficit in the earth’s remaining CO2 budget since January 2018.

But Thunberg said leaders from the United Nations wouldn’t suggest more radical plans to reduce emissions because they are “still not mature enough to tell it like it is.”

“You are failing us but young people are starting to understand your betrayal,” Thunberg said. “The eyes of all future generations are upon you and if you choose to fail us, I say we will never forgive you.”

Late on Monday, President Donald Trump retweeted a video of her speech, saying she "seems like a very happy young girl looking forward to a bright and wonderful future."

She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see! https://t.co/1tQG6QcVKO — Donald J. Trump (@realDonaldTrump) September 24, 2019

Earlier, Thunberg tweeted that she and 15 other children from around the world had filed a legal complaint, claiming that some countries have violated an approximately 30-year-old human rights treaty.

"Today at 11:30 I and 15 other children from around the world filed a legal complaint against 5 nations over the climate crisis through the UN Convention on the Rights of the Child," Thunberg tweeted.

The complaint was filed against nations who have ratified the treaty and have the largest emissions, she wrote. Those nations are Argentina, Brazil, France, Germany, and Turkey.

Following her speech, Thunberg's name began trending on Twitter, with many prominent figures and celebrities acknowledging her passion for the environment.

Thunberg arrived in the United States late last month after traveling across the Atlantic Ocean by sailboat in order to attend the climate summit.The trek, which took two weeks, was an emission-free way for Thunberg to travel from Europe to the United States.

Thunberg sprung to global prominence when she was 15, after she held her first climate strike outside the Swedish parliament last year, according to the BBC. Thunberg's protest, immortalized in a now-viral photo, inspired dozens of other climate strikes across the globe and gave her the platform to speak before several international bodies, such as the World Economic Forum, where she told world leaders: "I don't want you to be hopeful. I want you to panic."

"I want you to feel the fear I feel every day," she said. "And then I want you to act."

On Friday, Thunberg led 150 countries in a youth-led Global Climate Strike, which saw millions taking to the streets around the world to demand action and an end to the era of fossil fuels. Thunberg marched in New York City, where she addressed thousands of strikers.

"This is an emergency," she told the crowd. "Our house is on fire."