Swedish teenage climate activist Greta Thunberg joined thousands of youngsters in Madrid on Friday to protest against the lack of progress in tackling climate change even as a United Nations summit on the topic was under way in the city, AFP reported.

The 16-year-old activist joined the protests after making a nearly three-week journey across the Atlantic Ocean by catamaran. She does not take flights because of their carbon emissions.

World leaders gathered for the COP25 conference in Madrid to resolve disagreements on how to implement 2015 Paris agreement to avert catastrophic global warming.

“We would love some action by people in power because people are suffering and dying due to the climate and ecological emergency and we can’t wait any longer,” Thunberg said before the protests.

“The current world leaders are betraying us and we will not let that happen anymore,” she said, according to Reuters. “Change is coming whether you like it or not because we have no other choice.”

At a panel in the summit, Thunberg said the climate protests are getting “bigger and bigger” but that does not translate into any effective political action.

Thunberg said she hoped the two-week annual round of climate negotiations, which opened on Monday, would lead to some “concrete action” and that world leaders would understand the urgency of the climate crisis. “Of course there is no victory, because the only thing we want to see is real action,” she said. “So we have achieved a lot, but if you look at it from a certain point of view we have achieved nothing.”

The climate activist has rallied millions to her “Fridays for Future” movement and has demanded action on global warming repeatedly.

In September, she had furiously told world leaders at a one-day climate summit at the United Nations in New York that they had “stolen my dreams”. Next month, Thunberg had refused to accept an environmental award, saying the climate movement needed people in power to “listen” to “science” and “not any more prizes”.