London – Thousands of protesters took to the streets of London Monday, blocking traffic around the city in coordinated demonstrations demanding government action on climate change. It was the second climate change protest in the capital in four days.

"The recent science has been so shocking about what my children would face… that I feel we have to do whatever we can," 34-year-old Miriam, a property manager, told CBS News as she stood among a group of demonstrators blocking cars near London's Marble Arch. "This is an emergency."

Police officers are seen at an Extinction Rebellion protest at the Shell Centre in London, April 15, 2019. REUTERS

Activists stopped traffic in five central London locations. At the Shell oil company's London headquarters, a glass door was shattered and graffiti covered the walls. Protesters set up camp near Hyde Park, saying they were planning to stay for two weeks but would remain until their demands were met or they were forced out.

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"I'm ready to stay as long as necessary," 21-year-old Illana, a student who camped out overnight, told CBS News.

Monday's protests were organized by the group Extinction Rebellion, whose aim is "to act on the Climate and Ecological Emergency," according to their website. They have three demands: That the U.K. government declares a climate emergency, that it acts to reduce greenhouse gas emissions and biodiversity loss by 2025, and that it puts together a "citizens' assembly" to guide the legislative agenda around the issue of climate change.

Extinction Rebellion has emerged as one of the leading organizers of climate change action in the United Kingdom alongside the school strike movement, which has seen thousands of young people skip class to demand action on climate change. The school strikers were behind a protest last Friday.

Climate change protesters are demonstrating around London today. Here, they are blocking a major road. #ExtinctionRebellion #climatechange @CBSNews pic.twitter.com/tfmDHJIfro — Haley Ott (@haleyjoelleott) April 15, 2019

Since the group launched in 2018, Extinction Rebellion members have blocked bridges and stripped down to their underwear in Parliament. They declared their "international rebellion" would begin on Monday, and protests were expected in dozens of countries around the world.

"The movement's here now, whereas before there didn't seem to be something to join," Miranda, a 35-year-old primary school teacher, told CBS News. She was blocking traffic near London's Marble Arch with her husband and two young children. She said she was starting to get more involved in the fight against climate change.

"Brexit, none of it's going to matter if there's a climate apocalypse," she said.