PITTSBURGH (KDKA/CBS News) — Millions of people around the world, including Pittsburgh, walked out of their schools and workplaces today to demand urgent action on climate change.

The global climate strikes, which are taking place in more than 150 countries, were scheduled ahead of the opening of the United Nations General Assembly and the Climate Action Summit on Sept. 23.

The protests have been organized by young people around the world who are part of the “Fridays for Future” campaign, which has seen students walk out of their schools on Fridays to demand their political leaders take urgent action to address climate change.

“We need to act right now to stop burning fossil fuels and ensure a rapid energy revolution with equity, reparations and climate justice at its heart,” organizers say.

Climate activist Greta Thunberg will participate in the protests in New York City, where 1.1 million students have been given permission to skip school to join in.

WATCH: Pittsburgh Climate Change Strike —

Here in Pittsburgh, NextGen Pennsylvania organized the Pittsburgh Youth Climate Strike. It was held at the City-County Building downtown from 12-2 p.m.

Hundreds of Pittsburgh Public School students and other young people gathered on the portico to take part.

“It took the children to rise up to make everyone realize what a crisis we are in,” one attendee said. “I’m here to support the children.”

But not everyone here was on the same page.

Author and geologist Gregory Wrightstone is a climate change skeptic.

“I think these young people are being exploited by their parents and people that are using them to promote this failed notion of catastrophic man-man warming,” Wrightstone said.

(Photo Credit: KDKA)

Mayor Bill Peduto urged Pittsburghers, of all ages, to join in the march and rally.

Last night, the mayor said he would make himself available for a half an hour on the portico of the City-Council Building to sign permission slips for students that want to participate. However, his office was unsure whether he could legally sign the permission slips.

So, instead, the mayor offered to co-sign the slips that already have a parent or guardian signature.

“Pittsburgh Public Schools students need written permission from their parents or guardians to leave school, and Mayor William Peduto will co-sign such permission slips for youths interested in validating their attendance at the historic event, which millions of people are joining worldwide in more than 150 countries. The Mayor is urging PPS to excuse any student who has parent/guardian permission to attend the event.”

The rally and strike featured a large-scale sit-in at the City-Council Building and speakers from the Pittsburgh area organizations involved in global climate change and reform.

Pittsburgh Public Safety officials say the event was peaceful.

All roads have been reopened.

For more information on the rallies across the world, visit CBS News at this link.