Teen activist Greta Thunberg stuns in emotional UN climate speech

Teen activist Greta Thunberg has shocked the United Nations with an emotional speech, slamming adults for their failure to protect the environment.

"This is all wrong. I shouldn't be up here. I should be back in school on the other side of the ocean yet you all come to us young people for hope. How dare you," said the Swedish teenager, her voice quivering.

"You have stolen my dreams and my childhood with your empty words."

Thunberg was there to open the UN Climate Action Summit in the wake of protests across the world stemming from her weekly Fridays for Future strikes.

"For more than 30 years the science has been crystal clear. How dare you continue to look away, and come here saying that you are doing enough when the politics and solutions needed are still nowhere in sight," she said.

"You say you 'hear' us and that you understand the urgency. But no matter how sad and angry I am, I don't want to believe that. Because if you fully understood the situation and still kept on failing to act, then you would be evil. And I refuse to believe that."

Thunberg also had a brief run-in with United States President Donald Trump at the UN, after he showed up unexpectedly.

Video of the moment she spotted him has gone viral as she appears incredibly annoyed.

Trump has openly denied climate change and undone several regulations aimed at combatting emissions and global warming.

He has in the past suggested climate change can't exist because major snowstorms are still happening.

Thunberg said before arriving in the US she would not be meeting with the President as it would be a waste of her time.

"Why should I waste time talking to him when he, of course, is not going to listen to me?" she told CBS. "I can't say anything that he hasn't already heard."