Sixteen-year-old environmental activist Greta Thunberg told a crowd in North Carolina that climate change needs to be tackled “right now.”

The Charlotte Observer reports Thunberg spoke before an estimated 1,200 people gathered Friday in Charlotte. The Swedish teenager has been traveling across the U.S. since delivering a passionate speech at the United Nations Climate Action Summit in September demanding that world leaders do more to combat global warming.

In Charlotte, Thunberg was joined by ninth-grader Mary Ellis Stevens, who has held her own weekly calls to action outside a government building.

Thunberg urged the crowd to “unite behind science” and demand leaders to take responsibility.

Ten-year-old Georgia resident Gracey Eller attended the event. She says the issue matters to her because she wants “a future” for herself and children.