After two weeks of sailing, 16-year-old Swedish climate activist Greta Thunberg arrived in New York on Wednesday with an urgent call to action.

“The climate and ecological crisis is a global crisis, and the biggest crisis humanity has ever faced. And if we don’t manage to work together to cooperate… despite our differences, then we will fail. So we need to stand together,” Thunberg told a crowd of supporters who gathered to celebrate her arrival. “Let’s not wait any longer. Let’s do it now.”

Thunberg’s lonely protest outside the Swedish parliament building last August, and her persistent activism in the months since, sparked a wave of youth-led climate demonstrations across the world and inspired the global climate strikes set to kick off in over a 150 countries next month.

Organizers expect the strikes, scheduled to begin Sept. 20, to be the largest climate demonstration since the “Fridays for Future” movement launched—and maybe ever.

“Sea levels are rising, and so are we!” activists chanted as the emissions-free boat that carried Thunberg across the Atlantic approached New York.

Thunberg’s journey by boat, which stemmed from her refusal to fly due to the carbon emissions spouted by planes, garnered significant coverage from America’s major television networks, bringing more attention to the forthcoming week of global climate action.

Upon reaching shore, Thunberg said it is “insane that a 16-year-old has to cross the Atlantic Ocean to make a stand.” But in doing so, the Swedish environmentalist galvanized young people who are eager to take to the streets and force political leaders to act on the existential threat posed by the climate crisis.

“Something that’s really common among young people is a lot of time we just aren’t given that platform,” Shiv, a college sophomore, told Earther. “Now, Greta and millions of other kids are showing that we don’t need it handed to us. We can fight for the platform that we deserve and that our voices need to be heard.”

“On the 20th, we have three main demands as part of our coalition, which is no more fossil fuels, a just transition for frontline communities and for everybody in general, as well as holding fossil fuel executives accountable,” said Shiv. “I think a really big contribution [Thunberg] had is really making young people realize that we do have power, that we have the ability to change the conversation.”

Not wasting time following her arrival in the United States, Thunberg said she is planning to take part in a climate strike outside of the United Nations headquarters in New York City on Friday.

On Twitter, U.N. secretary-general António Guterres welcomed Thunberg to New York and applauded her commitment to confronting the planetary emergency.

“The determination and perseverance shown during your journey should embolden all of us taking part in next month’s Climate Action Summit,” said Guterres, referring to the U.N. event in New York on Sept. 23, which will come as people across the world strike for a livable future and pressure world leaders to take action in line with the urgent recommendations of the scientific community.

“We must deliver on the demands of people around the world,” Guterres said, “and address the global climate crisis.”