A flight to New York would've taken just eight hours, but Greta Thunberg wanted to prove a point on her two-week journey across the ocean. The teenage activist is sailing across the Atlantic as part of her campaign to highlight the need for action on climate change, and her voyage is almost complete.

Thunberg set sail from England two weeks ago aboard a zero-emissions yacht. When she arrives, the 16-year-old will be attending two climate summits at the United Nations and wants to raise awareness about environmental issues. Thunberg refused to fly to New York because of the carbon footprint of traveling by plane. Instead, she chose to sail about 3,000 miles.

Earlier Wednesday morning she tweeted that she can see the lights of New York, but won't actually touch shore until later this afternoon.

Land!! The lights of Long Island and New York City ahead. pic.twitter.com/OtDyQOWtF5 — Greta Thunberg (@GretaThunberg) August 28, 2019

"What I am concerned about is whether we will do something or not, whether the people in power will react and act with necessary force," Thunberg said before setting sail.

Gale-force winds meant it wasn't plain sailing to get to the United States. The 60-foot racing yacht, powered by underwater turbines and solar panels, was hit by heavy seas, but Thunberg made it across the Atlantic without raising carbon emissions.

Conditions on board included no showers and little privacy, but that didn't stop Thunberg from celebrating the one-year anniversary of the start of her climate change movement.

She began striking alone outside the Swedish parliament last August, and soon students around the world began walking out of school too, demanding action from their governments.

Thunberg became the unlikely leader of a global youth movement. She's been called "the voice of the planet," and has even been nominated for the Nobel Peace Prize.

"I want you to act as if the house is on fire, because it is," Thunberg said while addressing the World Economic Forum at Davos in January.

Earlier this month, she told CBS News that it's time to see if leaders in the U.S. and globally are really listening.

"They say they're listening to us, and now it is up to them to prove if they have listened," Thunberg said.

While she's here in the U.S., Greta will attend two global climate strikes in addition to the U.N. summits. It's still unclear how she plans to eventually travel back home.