Swedish climate activist Greta Thunberg has arrived in Portugal after sailing across the Atlantic in a catamaran for the past three weeks.

The 16-year-old originally sailed to the United States to attend UN climate talks this past August — travelling by sea as she avoids air travel due to carbon emissions that harm the environment.

Sailing out of Hampton, Virginia on Wednesday 13 November, Thunberg, as RTÉ News reports, joined navigator Nikki Henderson — the youngest ever skipper in the Clipper Race — on the 14m La Vagabonde along with its owners, an Australian family who document their adventures sailing around the world on YouTube.

La Vagabonde docked in Lisbon shortly before 2pm local time and later tonight (Tuesday 3 December) Thunberg will travel onwards to a UN climate summit in Madrid.

It's been 15 days since 16-year-old climate activist Greta Thunberg hitched a ride on a sail-powered yacht from Europe to the U.S. for the U.N. Climate Action Summit taking place in New York in mid-September. As Afloat previously reported, Thunberg has vowed to avoid air travel, due to environment-harming carbon emissions. The Malizia II docked this afternoon at 4:00 EDT at Coney Island in Brooklyn so its passengers could clear customs and immigration and then proceeded to North Cove Marina at the southern tip of Manhattan, just a stone's throw from Wall Street.

The Swedish teenager crossed the Atlantic on Boris Herrmann and Pierre Casiraghi’s Monaco-based 60ft Mono60, Malizia II, which has previously competed in the Rolex Fastnet Race.

Despite a light drizzle, a crowd of more than 200 gathered at North Cove to welcome Thunberg. The young activist has gained an adoring following in the last few months as she's worked, with great success, to highlight the urgency of the climate situation, which she says is most accurately described as a "crisis." She has 1.2 million followers on Twitter and 1.1 million friends on Facebook, and her Facebook post announcing her arrival in New York has drawn more than 2,000 comments, nearly all celebratory.

Young climate activist Greta Thunberg is taking to the high seas as she plans a zero-carbon journey from Europe to a UN climate summit in New York this September.

As RTÉ News reports, the 16-year-old Swede intends to cross the Atlantic on Boris Herrmann and Pierre Casiraghi’s Monaco-based 60ft Mono60, Malizia II, which has previously competed in the Rolex Fastnet Race.

The foiling vessel is equipped with solar panels and underwater turbines to generate energy at sea.

It will also bear the slogan ‘#Fridays for future’ inspired by Thunberg’s regular Friday protests against climate inaction at the Swedish parliament.

Thunberg refuses to fly due to the negative impact of commercial aviation on the environment.

RTÉ News has more on the story HERE.