By Ivana Kottasová, CNN

Greta Thunberg, the 16-year-old climate action advocate mobilizing the world against climate change, doesn't mince words. Not even when addressing the world's most powerful people.

"We are in the beginning of a mass extinction and all you can talk about is money and fairy tales of eternal economic growth," the Swedish climate activist told the United Nations General Assembly on Monday. "How dare you!"

Speaking during the UN Climate Action Summit in New York City, the 16-year-old, who arrived by traveling across the ocean in a carbon-neutral boat, was visibly frustrated with her audience and at times appeared to be holding back tears of anger.

Thunberg's message to the leaders was clear. Like many times in the past, she accused them of not doing enough to mitigate climate change. "For more than 30 years, the science has been crystal clear. How dare you continue to look away."

The Swedish schoolgirl rose to prominence because of her determination to persuade global leaders to take climate change seriously. She started with weekly sit-ins outside the Swedish Parliament, holding a handmade "School Climate Strike" sign. In just a few months, the one-girl protest grew into a worldwide movement with students walking out of schools in well over 100 countries.