To avoid travelling by air, Thunberg is making her trans-Atlantic trip on board the 60-ft yacht, the Malizia II, fitted with solar panels and underwater turbines that produce electricity onboard, with the aim of making the journey zero-carbon.

“I might feel a bit seasick and it’s not going to be comfortable but that I can live with,” Thunberg told BBC TV in Plymouth, southwest England, from where she is due to leave on Wednesday 14th, August.

“If it’s really hard then I just have to think it’s only for two weeks then I can go back to as usual,” said the 16-year-old who will be accompanied by her father, Svante, and a cameraman on the journey.

Earlier this month, the boat’s skipper told Reuters the teenage activist, who has become a figurehead for young environmental protesters, faced a challenging voyage on board the yacht which is designed for speed rather than luxury.

Image: Andreas Lindlahr, Courtesy of Team Malizia

There are no showers or toilets - those on board have to use a blue bucket.

“Greta taking on this challenge of sailing across on a race boat with zero comfort really shows her commitment to the cause and how far she’s willing to push herself,” skipper Boris Herrmann told Reuters.

He said they will try to make the journey as smooth as possible.

“By stopping flying you not only reduce your own carbon footprint but also that sends a signal to other people around you that the climate crisis is a real thing,” Thunberg said.

When she arrives, she will join the U.N. Climate Action Summit in New York in September and the COP 25 climate change conference in Santiago, Chile in December.

“Me speaking to the U.N. is not going to change the situation but if that can help to create awareness ... then I think that together we can try to ... make a change,” Thunberg said on a visit to a German anti-coal protest camp on Friday.