A 15-year-old stole the show at a U.N. climate conference in Poland late last week.

"Our civilization is being sacrificed for the opportunity of a very small number of people to continue making enormous amounts of money," teen activist Greta Thunberg of Sweden told conference attendees.

“You only talk about moving forward with the same bad ideas that got us into this mess even when the only sensible thing to do is pull the emergency brake,” she said. “You are not mature enough to tell it like it is.”

Delegates from almost 200 countries, including the United States, had gathered in Katowice, Poland, over the past two weeks to set rules to measure, report and verify efforts to cut emissions in line with the 2015 Paris agreement.

The deal cut Saturday, which requires developed and developing nations to follow similar guidelines, was a crucial outcome that could encourage the United States to return to the agreement, according to Andrew Light, of George Mason University.

But environmentalists such as Thunberg said the result was far from what was needed.

"We need to keep the fossil fuels in the ground," she stated flatly.

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Jake Schmidt of the Natural Resources Defense Council also said that not enough was done: "Climate change is here and getting worse faster than expected, and that’s why the world needs to move from slow-walking climate action to sprinting."

Calling out the United States' foot dragging, Helen Mountford of the World Resources Institute said "the Trump administration’s efforts to highlight fossil fuels is out of step with the American public that wants real progress on climate change."

Thunberg's words delivered a powerful message that global leaders should not ignore, Mountford said.

Thunberg, who calls herself a "15-year-old climate activist with Asperger's," said she was inspired by school walkouts in the United States that followed a deadly school shooting in Parkland, Florida, CNN reported.

"We have come here to let you know that change is coming, whether you like it or not, she said. "The real power belongs to the people."

Contributing: John Bacon, USA TODAY