Greta Thunberg is sailing back across the Atlantic. Here's what she accomplished while in the US

Swedish teen climate activist Greta Thunberg is heading back across the Atlantic Ocean. She's hitching a ride on a sailboat with Australian YouTubers after nearly three eventful months spreading her climate message across North America.

Among other events, she joined in climate strike rallies and protests from California to Colorado to North Carolina to Montreal.

Thunberg has become a symbol of a growing movement of young climate activists after leading weekly school strikes in Sweden that inspired similar actions in about 100 cities worldwide.

Thunberg is sailing back to Europe aboard La Vagabonde, a 48-foot catamaran operated by Riley Whitelum and Elayna Carausu. The Australian couple are documenting their journey around the world on the YouTube channel “Sailing La Vagabonde” and responded to Thunberg’s tweet for help crossing from the U.S. back to Europe.

In August, the teen activist sailed across the Atlantic Ocean to the United States on a zero emissions sailboat. She has been a vocal critic of flying because it contributes to the greenhouse gas emissions that accelerate global warming.

Here's a look back on her time in North America:

Greta scolds the United Nations: 'I shouldn't be up here'

In September, Greta gave an impassioned speech before the United Nations Climate Action Summit, where she scolded world leaders for not acting quickly and decisively to combat climate change.

"This is all wrong. I shouldn't be up here. I should be back in school on the other side of the ocean," she said.

"People are suffering, people are dying, entire ecosystems are collapsing ... and all you talk about is money and eternal fairy tales of economic growth. How dare you?" she said.

Greta to US lawmakers: Do something

In the United States, Thunberg participated in climate protests in New York City, Iowa City, Los Angeles, Charlotte and Denver.

She also testified before the U.S. Congress in September before a joint hearing of two House committees on the global climate crisis.

During the hearing, she had a simple message for American lawmakers: Do something.

Instead of planning a lengthy opening statement to start the hearing, Thunberg simply offered a copy of the 2018 global warming report by the Intergovernmental Panel on Climate Change that emphasizes the dire threat that human-caused global warming poses, along with the climate and economic impacts.

"I am submitting this report as my testimony because I don’t want you to listen to me," Thunberg told lawmakers. "I want you to listen to the scientists. And I want you to unite behind the science. And then I want you to take real action."

UN report: World's oceans and mountains are in big trouble from climate change

Greta rallies at climate protests

Thunberg had been traveling across the United States and Canada, appearing on “The Daily Show With Trevor Noah” in New York, protesting alongside Sioux leaders in North Dakota, bike riding in Santa Monica, Calif., with Arnold Schwarzenegger, and joining school strikes every Friday, The New York Times reported.

During a speech in Iowa City, Thunberg hammered the absurdity of it taking teenagers to make public figures take action locally and internationally.

"We teenagers and children shouldn't have to take the responsibility, but right now the world leaders keep acting like children and someone needs to be the adult in the room," Thunberg said. "The world is waking up. We are the change, and change is coming whether they like it or not."

Climate change: Meet 15 other young climate activists taking on world leaders

While in Canada, Thunberg participated in climate protests in Montreal, Edmonton and Vancouver. The protest in Montreal was one of the largest in the city's history, according to Global News. When she looks back on her time in the U.S. and Canada, Thunberg said, the things that stick out the most include a glacier in Canada’s Jasper National Park that is destined to disappear “no matter what we do.”

A visit to the Standing Rock Indian Reservation, where there have been protests over a pipeline, also left an impact.

Climate change: Over 11,000 scientists around the world declare a 'climate emergency'

And now, Greta sails back to Europe

Before it was canceled due to mass protests, Thunberg had also planned to attend the COP25 Climate Change Conference in Santiago, Chile, in December, the BBC reported.

"I was on my way to Mexico to continue my overland trip from the Climate Action Summit in New York to Chile. So I reached out on social media to ask if anyone could help me find transport back to Europe," Thunberg said Tuesday.

The trip could take two to four weeks, in conditions that could be challenging. November is considered offseason for sailing across the Atlantic.

"Of course finding a boat ready to sail back across the North Atlantic in late November is not easy," she said. "But it’s amazing to see how many people there are who are willing to help, like Riley, Elayna and Nikki (Henderson). By sailing, I once again want to highlight the fact that it’s basically impossible to live sustainable in today’s societies."

Though she said she may not make COP25 in time,"it doesn’t really matter if I get there in time or not. There are countless other activists who will speak there and deliver the same message as I would.

"And it’s not like my voice is irreplaceable," Thunberg said. "I’m really looking forward to this sailing trip and getting back on the ocean. This is an amazing opportunity and I am extremely grateful to have the privilege of experiencing these kinds of things."

Contributing: Ryan W. Miller and Savannah Behrmann, USA TODAY; Zachary Oren Smith and Aimee Breaux, The Iowa City Press-Citizen; The Associated Press

This article originally appeared on USA TODAY: Greta Thunberg: Climate activist sails to Spain aboard La Vagabonde