Portland students joined the worldwide Global Climate Strike demonstration Friday to call on leaders to do something about climate change.

Between 1,500 and 2,000 young people skipped school to chant, wave signs and speak out at a gathering outside Portland City Hall. The crowd overflowed from the sidewalk, prompting police to close the street.

THANKS TO OUR SPONSOR: Become a Sponsor

It was one of more than 1,700 such protests planned in 112 countries.

Reynolds High School student Victoria Clark says she came out to show what an urgent issue climate change is for her and many other young people.

"I’m here today because we only have so long to fix what is going on with our climate," she said.

The burning of fossil fuels like coal and petroleum have produced billions of tons of carbon dioxide and other greenhouse gases, which trap heat in the atmosphere. This is causing average temperatures to rise — with consequences that range from more intense winter storms, rising sea levels, melting glaciers and ice caps, longer wildfire seasons, and changes in the ocean's chemistry.

Scientists have been warning about climate change since the 1980s, well before most of the Portland protest's participants were born.

THANKS TO OUR SPONSOR: Become a Sponsor

Jaden Winn, a sophomore at Wilson High School, said the global demonstration by people his age illustrated how his parents generation and those before them have not stepped up.

"They're not doing what they need to do. That's been been left to us," Winn said in an interview with OPB's "Think Out Loud" host Dave Miller.

Your browser does not support the audio element.

The students hope that by protesting, they'll provide a face to the climate crisis and motivate legislators to act. Many referenced the United Nations Intergovernmental Panel on Climate Change, which warned in October that we may only have 12 years to act on climate change and limit warming to 1.5 degrees Celsius.

Participants in the Portland event wore shirts and held signs that said, "We have until I'm 24 to stop this" and "I'll be 20 when the damage is irreversible."

Portland students hold a sign during the Global Climate Strike in front of Portland City Hall. Kaylee Domzalski / OPB

Charlie Abrams, a 15-year-old freshman at Cleveland High School, has been a climate activist since he was 11. He told "Think Out Loud" that he was encouraged by the vast number of youths who turned out for Friday's event. He said he's seen a dramatic increase in the level of activism by his generation to do something about the threat of climate change.

"We're not only the ones affected by this the most, but our voice stands out in a crowd of adults," he said.

The rally was scheduled to last until noon, followed by a march. But by 11:30 a.m. the crowd had grown so large that City Commissioner Jo Ann Hardesty ended the rally. Then the students marched a few blocks to Tom McCall Waterfront Park. When the march began, the crowd stretched for several city blocks.

Portland Public Schools leaders say that while they encourage students to be engaged politically, any students who walk out will be marked as absent. But students say that walking out of school makes a bigger impact.

"I know people will say that we're just skipping school, that we're just being lazy. But we're taking the action that legislators won't," Clark said.