STOCKHOLM: Teen climate activist Greta Thunberg was back protesting outside the Swedish parliament on Friday, the three-year anniversary of her first school strike which grew into a global, youth-led protest movement.

Thunberg's grassroot initiative caught on around the world, with millions rallying at weekly "Fridays for Future" protests to call on world leaders to listen to scientists about, and act to stop, climate change, and in 2019 the Time magazine named her person of the year.

Thunberg, who took a sabbatical from school in 2019 before starting high school, told Reuters on Friday her movement was far from achieving its goals.

"In one way of course I haven't achieved anything," she told Reuters. "In another way I have made lots of friends within the movement and we have been able to organise mass protests and it feels like more people are starting to wake up and demand change."

Her first protest outside parliament in August 2018 at the age of 15 "felt quite lonely," she said. "But it also felt very good to be actually doing something."

Thunberg was joined on Friday in Stockholm by several fellow activists who travelled from Europe to mark the day.

"We decided to unite today ... to strike together, to plan, to look at what's up next," said activist Luisa Neubauer, 25, from Germany, where general elections are scheduled for Sept. 26. 

"I'm also here in the midst of the German election campaign, so that's a big thing. Germany is a huge player, we have a huge responsibility, and right now all players are failing to live up to that responsibility," Neubauer said.

A recent U.N. climate panel report said global warming was dangerously close to spiralling out of control.

During her sabbatical year, which she took to advocate her cause full-time, Thunberg gave a speech to world leaders at a U.N. Climate Action Summit.