The Swedish climate activist joined a climate strike in the US city of Denver where she told the crowd: "We are the change".
Some believed she was a favourite to win the Nobel Peace Prize, announced yesterday, for her effort to get young people worldwide to fight climate change.
But instead, that award went to Ethiopian Prime Minister Abiy Ahmed for his work to bring peace to that region of Africa.
Head of the Peace Research Institute Oslo, Henrik Urdal, omitted Ms Thunberg from the Nobel Peace Prize shortlist he publishes.
He explained his decision to The Washington Post, saying there "isn't scientific consensus that there is a linear relationship between climate change — or resource scarcity, more broadly — and armed conflict."
Despite her loss, an enthusiastic crowd of thousands cheered Ms Thunberg on at the event near the Colorado state Capitol.
Speaking at the protest, Ms Thunberg said: "It is we young people and future generations who are going to suffer the most from the climate and ecological crisis."
"It should not be up to us to take the responsibility but since the leaders are behaving like children then we have no other choice."
The rally included speeches and songs from youth activists and a moment of silence to remember those people facing danger and death because of climate change.
Ms Thunberg said she and fellow youth activists would not beg those in power to act because she expected leaders to keep ignoring them.
"We will instead tell them, if they won't do it, we will," the 16-year-old said to loud cheers.
"The world is waking up and we are the change. The change is coming whether you like it or not."
Ms Thunberg began holding solitary demonstrations outside Sweden's Parliament in August 2018, skipping classes once a week to protest against climate change.
She has staged weekly "Fridays for Future" demonstrations for a year, inspiring students around the world to skip classes on Fridays to demonstrate as well.
She sailed to the US in August to promote her climate change campaign and garnered international attention when she scolded world leaders at the United Nations last month.
Ms Thunberg will continue touring the Americas for several months, concluding with a UN climate conference in Chile in December.
سایت تابناک از انتشار نظرات حاوی توهین و افترا و نوشته شده با حروف لاتین (فینگیلیش) معذور است.