Video report by ITV News Science Editor Tom Clarke
Climate change activist Greta Thunberg has set sail to cross the Atlantic in a carbon-neutral yacht.
The 16-year-old has been invited to attend UN summits on global warming in New York and Chile.
Before she set off from Plymouth, Greta admitted the voyage would be "challenging for everyone on the boat", adding "that is what you have to expect".
The trip on the high-tech racing yacht Malizia II will take around two weeks, and the vessel itself has no refrigerator, kitchen or toilet.
The 60ft yacht is fitted with solar panels and underwater turbines which generates zero-carbon electricity on board. Greta decided against travelling by plane to reduce her carbon footprint and impact on the environment.
Speaking about the lack of toilet on board the boat, Greta said: "We will have to do it in a bucket but it's fine.
"We have a small heating and we boil our water in freeze-dry bags and eat that, and that is quite good.
"I don't need fancy food."
The vessel is captained by Boris Herrmann, and Greta will also be accompanied on the two-week journey by a filmmaker, her father Svante and Pierre Casiraghi, the grandson of Monaco's late Prince Rainier III and American actress Grace Kelly.
The teenager shot to prominence in 2018 when she started to boycott school on Fridays outside the Swedish parliament.
Her boycott continues to this day, where she still hasn't attended school on a Friday.
Greta is taking a sabbatical year from school and will join large-scale climate demonstrations and speak at the UN Climate Summit, hosted by secretary-general Antonio Guterres in New York in September.
She is also planning on visiting Canada and Mexico before travelling to this year's UN climate conference, where she will make her journeys by train and bus.