Lisbon (Portugal), Dec 3 (AP) Climate activist Greta Thunberg arrived in Portugal on Tuesday after a three-week voyage across the Atlantic Ocean, telling cheering supporters that the journey had "energised" her for the fight against climate change.

The Swedish teen, whose one-woman protests outside the Swedish parliament helped inspire a global youth movement, sailed into the port of Lisbon after making a last-minute dash back from the United States to attend this year's UN climate conference.

Thunberg has been steadfast in her refusal to fly because of the amount of greenhouse gases emitted by planes, a stance that put her planned appearance at the meeting in doubt when the venue was moved from Chile to Spain a month ago.

"We've all been on quite an adventure," Thunberg told reporters shortly after stepping off the catamaran La Vagabonde, on which she'd hitched a ride back home to Europe.

"It feels good to be back."

Thunberg's appearances at past climate meetings have won her plaudits from some leaders — and criticism from others who've taken offense at the angry tone of her speeches.

"I think people are underestimating the force of angry kids," Thunberg said.

"If they want us to stop being angry, then maybe they should stop making us angry."

The 16-year-old said she planned to spend several days in the Portuguese capital before heading to Madrid, where delegates from nearly 200 countries are discussing how to tackle global warming.

"We will continue the fight there to make sure that within those walls the voices of the people are being heard," she said.

The white 48-foot (15-meter) yacht carrying Thunberg, her father Svante, an Australian family and professional sailor Nikki Henderson sailed into Lisbon amid blue skies, with a small flotilla of boats escorting it to harbour.

Her trip contrasted with the many air miles flown by most of the UN meeting's 25,000 attendees.

Thunberg wanted a low-carbon form of transport to get to the climate meeting, which was switched at short notice to Spain from Chile due to unrest there.

The yacht leaves little or no carbon footprint when its sails are up, using solar panels and hydro-generators for electricity.

"I am not traveling like this because I want everyone to do so," said Thunberg. "I'm doing this to sort of send the message that it is impossible to live sustainable today, and that needs to change. It needs to become much easier."

She said bringing her critical message to political leaders can feel awkward.

"I feel strange when I get applauded by people in power ... because it's obvious that it's them I'm criticising but they can't show that in front of the cameras," she said.

"It's quite funny sometimes."

Looking ahead to next year's presidential election in the United States, Thunberg said: "I just hope that someone wins that can think on the long term, not just the short term."

Chile's Environment Minister Carolina Schmidt, saluted Thunberg's role speaking out about the threat of climate change.

"She has been a leader that has been able to move and open hearts for many young people and many people all over the world," Schmidt told The Associated Press at the summit in Madrid.

"We need that tremendous force in order to increase climate action," she said.

Near to the conference, some 20 activists cut off traffic in central Madrid and staged a brief theatrical performance to protest climate change.

Members of the international group called Extinction Rebellion held up a banner in Russian that read: "Climate Crisis. To speak the truth. To take action immediately."

Some activists jumped into a nearby fountain while others threw them life jackets. They chanted: "What Do We Want? Climate Justice."

Others dressed in red robes with their faces whitened to symbolise the human species' peril danced briefly before police moved in to end the protest.

Meanwhile, the UN weather agency released a new report showing that the current decade is likely to set a new 10-year temperature record, providing mounting evidence that the world is getting ever hotter.

Preliminary temperature measurements show the years from 2015 to 2019 and from 2010 to 2019 "are, respectively, almost certain to be the warmest five-year period and decade on record," the World Meteorological Organization said.

"Since the 1980s, each successive decade has been warmer than the last," the agency said.

While full-year figures aren't released until next March, 2019 is also expected to be the second or third warmest year since measurements began, with 2016 still holding the all-time temperature record, it said.

This year was hotter than average in most parts of the world, including the Arctic. "In contrast a large area of North America has been colder than the recent average," the UN said.

The World Meteorological Organization's annual report, which brings together data from numerous national weather agencies and research organizations, also highlighted the impacts of climate change including declining sea ice and rising sea levels, which reached their highest level this year since high-precision measurements began in 1993. (AP)

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