Swedish teen activist Greta Thunberg said on Tuesday that US President Donald Trump’s climate change denialism was “so extreme” that it had helped galvanise the movement to halt long term planetary warming.

She spoke in an interview with AFP on the eve of her departure from North America, where she has spent almost three months.

“He’s so extreme and he says so extreme things, so I think people wake up by that, in a way,” the 16-year-old said on board a sailboat preparing to depart from the East Coast town of Hampton, Virginia for Europe early on Wednesday.

“I thought when he got elected, now people will finally, now people must finally wake up,” she continued.

“Because it feels like if we just continue like now, nothing’s going to happen. So maybe he is helping.”

A young Australian couple volunteered to aid her in her return journey.

Elayna Carausu, 26, and Riley Whitelum 35, who live on a catamaran with their 11-month-old boy and document their adventures on social media, responded to Greta’s appeal for help with an environmentally friendly return trip to Europe.

They had originally planned to spend the winter in the US but will now carry Greta and her father Svante Thunberg on their 14m catamaran La Vagabonde.

After months of campaigning in the US and Canada, including an appearance at a key UN climate summit in September, which was the reason for her visit, she offered a lukewarm assessment on the impact.

“It depends,” she said, in her usual matter-of-fact way of speaking. “In one way, lots of things have changed, and lots of things have moved in the right direction, but also in a sense we have gone a few more months without real action being taken and without people realising the emergency we are in,” said the high-schooler, who will return to education next year.

The trip itself should last two to three weeks, depending on weather conditions. The young couple and their son Lenny, who has his own Instagram account, and the Thunbergs will be joined by professional British sailor Nikki Henderson, who was called on to lend a hand.

Their destination is Portugal, some 5,500km away, in order to participate in the COP 25 UN climate summit in Madrid, Spain from December 2-13.

“If I get to the COP 25 in time then I will participate in that, because I have received an invitation to do so,” she said. “And then I will go home, I think.”