PLYMOUTH, UNITED KINGDOM - A year after starting a school strike that made her a figurehead for the fight against global warming, Greta Thunberg believes her uncompromising message is getting through -- even if action remains thin on the ground.

The 16-year-old Swede, who sets sail for New York on Wednesday to deliver her demand for climate action to North America, has been a target of abuse but sees that as proof she is having an effect.

"The debate is shifting. I feel like people are taking this more urgently, people are starting to be more aware, slowly," she told AFP on board the 60-foot yacht taking her across the Atlantic.

However, she admits this still needs to be matched by action, warning: "When you see the big picture almost nothing positive is happening."

Since she made headlines by skipping school to protest outside the Swedish parliament in August last year, Thunberg has met political and business leaders across Europe.

Now she is heading to the United States to attend a UN climate summit in New York in September -- and as she refuses to fly, she's been offered a lift on a racing yacht.

Malizia II will be skippered by Pierre Casiraghi, a member of the Monaco royal family, and German sailor Boris Herrmann.

The facilities are basic -- the toilet is a bucket, there is no kitchen -- but it has solar panels and underwater turbines that allow it to operate without producing carbon emissions.

Thunberg -- who has never sailed before this week -- will be onboard for two weeks, along with her father Svante and a filmmaker.

"It just shows how impossible it is to live sustainably today -- it's absurd that you have to sail across the Atlantic Ocean like this to get there with no emissions," Thunberg said in the English port of Plymouth.

"But I feel like since I'm one of the few people in the world who can actually do this I want to take that opportunity to do it."

She has no plans to meet with President Donald Trump in the US, saying: "I can't say anything that he hasn't already heard." -AFP