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Avery Tsai, a 9-year-old vegetarian from Brooklyn, isn't in her fourth-grade class. Instead, she's marching in the streets to demand the adults around her take climate change seriously.

“I’m here to fight climate change, for my future, to solve all the climate change problems,” she told VICE News from Manhattan’s Foley Square. New York schools gave the city's students permission to skip class Friday to attend the demonstrations, and tens of thousands showed up.

“Strike more, march more, reduce your pollution,” Avery said, when asked how she’d solve the crisis.

“Speaking to the older generation, I would say, ‘Get your shit together.'"

Her peers around the world agree with her. At least 5,000 strikes in more than 150 countries are scheduled for Friday, led by 16-year-old Swedish activist Greta Thunberg. Altogether, the demonstrations are shaping up to be the biggest environmental protest in history. The young activists had read the apocalyptic reports, published one after the other, warning humanity will face rising tides, mass migrations, famines, droughts, floods, fires if carbon emissions don’t fall — and quickly. And they listened.

Many of the elementary and middle school students at the march could clearly articulate what climate change is and why it should be fought. And the 20-year-olds were debating whether a carbon tax was the best way to curb emissions. They know their climate science and their economics — because they know their future depends on knowing.

“There are a lot of neoclassical economists who feel they have solved the climate crisis academically. They say that the solution to climate change is a carbon tax,” said Brian Conwell, a 20-year-old from Dutch Harbor, Alaska. He’s not convinced, though. A carbon tax, alone, he said, is too one-dimensional.

Niyyah Cosner and Hannah Mayerfield, both 14, attend the Global Climate Strike in New York's Foley Square. It's expected to be the largest environmental protest in history. (Alex Lubben/VICE News)

Sixteen-year-olds Sophie Andersen, Elizabeth Merryweather, and Jonathan Palash-Mizner had all followed coverage, or read in its entirety, the most recent Intergovernmental Panel on Climate Change report. Its authors recommended that the world cut its greenhouse gas emissions in half by 2030 to avoid the most catastrophic consequences of climate change.

They’re now figuring out whether an economy that prioritizes profit over the environment is compatible with fighting climate change. To them, it doesn’t seem to be.

“I think that capitalism is just going to lead to cancerous growth,” said Louis Roberts, a 19-year-old from Becket, Massachusetts. “Anything short of reining in the private sector extensively is not going to work.”

These young protesters are taking after Thunberg, who started all of this with her solo strikes every Friday outside the Swedish Parliament starting back in August 2018. Others — like Alexandria Villaseñor, who’s been striking every Friday outside the United Nations building in New York — soon joined her.

"If there is one day you should join, this is the day,” Thunberg told Teen Vogue.

Thunberg doesn’t fly on airplanes. The carbon footprint, she says, is too great. So she took a solar-powered high-speed sailboat to the U.S. from Sweden. And she’s been busy since she got to the states. On Wednesday, she appeared before Congress, where she roasted climate lawmakers for not doing enough and begged them to listen to scientists.

Avery Tsai, 9, and Elizabeth Payne hold signs in Foley Square in Manhattan, New York, for the Global Climate Strike. (Alex Lubben/VICE News)

In two days, the United Nations will convene its own Climate Action Summit, which starts on Sept. 23. There, countries are expected to ramp up their commitments to cut their greenhouse gas emissions under the Paris Climate Agreement. And the thousands of kids around the world are hoping their protests — and clever signs — will catch the U.N.’s attention.

“I believe it’s 71% of emissions are produced by 100 companies,” said Merryweather, correctly. “The government needs to put in restrictions.”

As these young people have ramped up their activism, the public conversation around climate change has begun to shift. To start, they’re pushing for The Green New Deal, a sweeping plan from Rep. Alexandria Ocasio-Cortez to retool the economy to confront the climate crisis. She’s a hero to many of the young activists. Since the plan’s introduction in February, all the leading Democratic presidential candidates have embraced the idea.

“Something that I strive for is trying to create a more inclusive climate movement,” said 20-year-old Tasha Elizarde. “There are a lot of instances in which we don't talk enough about certain groups of people that are impacted by climate change.”

This isn’t the first time the kids have gone on strike for the climate. Back in March, students in at least 100 countries walked out of their classrooms for the same reason. Another strike is scheduled for next week, at the end of the U.N.’s summit on Sept. 27.

Young strikers gather in downtown Manhattan, as speakers prepared to take the stage as part the Global Climate Strike. (Alex Lubben/VICE News)

But Friday’s protests are the largest so far — and specific to the challenges facing their countries. In Nepal, the young activists will call attention to the climate impacts on the Himalayas. In Bangladesh, they’ll be mobilizing communities who live near polluting coal plants. In the Democratic Republic of Congo, they’ll be calling on the president to respect the country’s conservation laws.

And adults will be there too. Around 1,500 Amazon workers are expected to walk off the job Friday to protest the company’s climate policies — the day after CEO Jeff Bezos announced a plan to make his mega-corporation carbon-neutral by 2040.

Despite some support from the older generation, the young protesters wouldn’t let them off the hook.

“Yes, I’m pissed,” Palash-Mizner said, holding a megaphone emblazoned with “Extinction Rebellion” stickers in Foley Square. He’d given them out in the subway to encourage people to come out and strike.

“Speaking to the older generation, I would say, ‘Get your shit together,’ because we don’t have the time,” he said. “But this shouldn’t be happening. This should be the older generation’s job.”