Greta Thunberg has arrived in Portugal after a three-week voyage across the Atlantic Ocean, telling cheering supporters the journey had “energised” her in the fight against climate change.

The Swedish teenager, whose solo protests outside the Swedish parliament helped inspire a global youth movement, sailed into Lisbon on a voyage from the US to attend this year’s UN climate conference.

She has been steadfast in her refusal to fly because of the amount of greenhouse gas 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,” she told reporters shortly after stepping off the catamaran La Vagabonde, on which she had hitched a ride back to Europe. “It feels good to be back.”

Her appearances at past climate meetings have won her plaudits from some leaders — and criticism from others who have taken offence at the angry tone of her speeches.

“I think people are underestimating the force of angry kids,” Greta 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 48ft yacht carrying Greta, her father Svante, an Australian family and professional sailor Nikki Henderson sailed into Lisbon under 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.

Greta wanted a low-carbon form of transport to get to the climate meeting, which was switched at short notice 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 travelling like this because I want everyone to do so,” said Greta. “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.”

Greta Thunberg arrives in Lisbon
Greta Thunberg arrives in Lisbon (Pedro Rocha/AP)

Chile’s environment minister Carolina Schmidt, saluted her 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,” Ms Schmidt said at the summit in Madrid.

“We need that tremendous force in order to increase climate action.”

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

Preliminary 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 Organisation said.

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

While full-year figures are not released until March, 2019 is also expected to be the second or third warmest year since measurements began, with 2016 still holding the all-time 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 Organisation’s annual report, which brings together data from numerous national weather agencies and research organisations, 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.