At the opening of the UN summit on the climate emergency, activist Greta Thunberg has sharply criticized the inaction of the leaders of the planet.

"You let us down!" On Monday, young climate activist Greta Thunberg called on world leaders gathered at the UN for a climate emergency summit to reinvigorate the Paris agreement. The young Swede set the tone in opening, blaming the heads of state for their inaction.

"Whole ecosystems collapse, we are at the beginning of mass extinction, and all you are talking about is money, and fairy tales of eternal economic growth? How dare you!" she said indignantly. The young activist again recalled in her speech the scientific facts that confirm the accelerated global warming, pointing out the lack of reaction of the leaders who stood before her. "For more than 40 years, science has been crystal clear, how do you dare look elsewhere and come here claiming that you're doing enough?" You say you hear us and you understand the urgency but I do not want to believe it, "she said.

>> Listen to his speech at the UN:

WATCH: Greta Thunberg passionately shares her message to world leaders at #UNGA:

"We'll be watching you ... We're going to meet you in the world." pic.twitter.com/Z0XuVvcIXK

- NBC News (@NBCNews) September 23, 2019

Committed youth

Greta Thunberg's speech reinforces a little more the symbol that she represents of a world youth engaged and revolted against the inaction of the political leaders. "You've let us down, but young people are beginning to understand your betrayal," Greta Thunberg said, pointing to her own commitment and that of her generation. "I should not be here, I should be at school, on the other side of the ocean (...) You stole my dreams and my childhood with your empty words."

The activist responded to the invitation of United Nations Secretary-General Antonio Guterres. He reminded the preamble of the summit that 66 states had now subscribed to the principle of carbon neutrality by 2050. Carbon neutrality means that countries commit to reduce their emissions as much as possible and to compensate for the remainder, for example in Europe. replanting trees, which absorb carbon from the air. So far, however, only about 20 countries have included this horizon in their national law or initiated this process.

Surprise appearance of Donald Trump

Donald Trump, present at the UN for other events, made a surprise appearance at the climate summit. he came to sit a few minutes in the room, while the United States declined his invitation. He listened and then applauded Indian Prime Minister Narendra Modi before heading off to another event. The brief visit of this president who had withdrawn the United States from the Paris agreement with a big noise has caused the assembly's perplexity.