Swedish teen climate activist Greta Thunberg is scheduled to set sail from the British city of Plymouth to attend a series of climate summits and protests in the United States.
Thunberg, 16, who refuses to fly because of the CO2 that aviation emits, will be travelling from Wednesday on the Malizia, a racing yacht captained by German sailor Boris Herrmann and Pierre Casiraghi of Monaco.
Thunberg plans to attend the UN Climate Action Summit in New York on September 23 on the sidelines of the UN General Assembly, as well as climate protests planned for September 20 and 27.
The teen has galvanised young people across Europe and beyond with her activism since she began a weekly school strike outside the Swedish parliament a year ago.
It has snowballed into a global movement demanding action on climate change under the "Fridays For Future" slogan.
Her father Svante Thunberg and filmmaker Nathan Grossman were also to join the voyage, which is dependent on weather conditions.
She will also visit Canada and Mexico before joining the annual UN climate change conference hosted by Chile in December.
Herrmann has said he considered his role in Thunberg's trip a big responsibility. It will be her first-ever sailing trip.
All electricity on board the Malizia is generated from solar panels and underwater turbines.
Conditions on the yacht are spartan. Herrmann says the ship has no toilets on board, and only thin, tube-like bunks for beds.
Australian Associated Press