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Environmental campaigner Greta Thunberg is known for her strong speeches on climate change.

And the 16 year old has delivered yet another powerful message to world leaders - this time at the United Nations Climate Action Summit in the United States.

UK Prime Minister Boris Johnson is amongst those at the meeting in New York.

She's asked world leaders to do more to tackle the problem: "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."

Greta added: "You are failing us. But the young people are starting to understand your betrayal. The eyes of all future generations are upon you. And if you choose to fail us, I say, we will never forgive you. We will not let you get away with this. Right here, right now is where we draw the line. The world is waking up, and change is coming whether you like it or not. Thank you."

Greta made her speech after sailing from the UK to New York rather than travelling by plane.

The summit also comes after the activist inspired millions of young people to join a global climate strike.