She refuses to fly due to carbon emissions.
Greta Thunberg set sail for New York on Wednesday, heading for a UN summit on a zero-emissions yacht.
The two-week crossing will likely not be without danger as she traverses the Atlantic during hurricane season in the yacht.
She's making the trip to add her high-profile voice to two appeals for great emissions cuts; the Climate Action Summit in New York on 23 September and the the UN climate conference in Santiago in early December.
The 16-year-old who has inspired a whole generation of young activists, refuses to fly due to the carbon emissions produced by planes.
She has become a magnet for criticisms that are likely only to intensify when she arrives in the US for next month’s UN climate summit in New York.
The teenager said of climate sceptics: "There's always going to be people who don't understand or accept the united science, and I will just ignore them, as I'm only acting and communicating on the science."
She said she thought people's mindsets were changing "even if it's not enough, and not fast enough, that's something, it's not for nothing".
The yacht is skippered Pierre Casiraghi, vice president of the Monaco Yacht Club and a member of the principality’s ruling family, and German round-the-world sailor Boris Herrmann.
