Greta Thunberg, the 16-year-old Swedish environmental activist who launched a school strike in 2018 that culminated into an international movement, has been sailing for the past three weeks again.

This latest voyage across the Atlantic comes months after Thunberg's emotional speech at the United Nation's Climate Action Summit in September, where she lashed out at world leaders' for letting the younger generation down in their climate inaction.

It's not just talk, of course.

Thunberg arrived at the Summit in New York back in September via a high-tech, zero-emissions sailboat as she refused to take a plane due to the high carbon emission caused by traditional aviation methods.

Sailing expedition

She was supposed to continue sailing from New York to Chile to attend the 2019 United Nations Climate Change Conference (COP 25), but the venue subsequently changed to Madrid, Spain, due to the Chilean social unrest.

This unanticipated change affected the voyage of Thunberg causing her to take to social media to appeal for help.

As #COP25 has officially been moved from Santiago to Madrid I’ll need some help.
It turns out I’ve traveled half around the world, the wrong way:)
Now I need to find a way to cross the Atlantic in November... If anyone could help me find transport I would be so grateful.
-> https://t.co/vFQQcLTh2U

— Greta Thunberg (@GretaThunberg) November 1, 2019

Fortunately, she managed to hitch a ride to Madrid with two Australian YouTubers, who had been sailing around the world for the past five years.

After three weeks at sea, Thunberg arrived at Lisbon, Portugal on Dec. 3, 2019, where she had a press conference at the port sharing her thoughts from ruminating for the past few weeks at sea.

Sustainable lifestyle should be made easier today

Thunberg said that the voyage is meant to send a message that "it is impossible to live sustainably today", but not to ask everyone to travel in the same way.

This is why the sustainable lifestyle should be made easier today as relying on people to sail across the ocean like this is "absurd".

She added that "people are underestimating the force of angry kids", which drew a round of cheers and applause from youth activists and crew members at the scene.

To not make the young people angry, Thunberg said that the people in power should listen to scientists.

The children, however, are incapable of presenting plans so they are banding together in support of the science.

Thunberg urged everyone to work together to secure the future living conditions for future generations in light of the climate emergency.

Around 25,000 people from 200 countries are expected to attend the COP25 climate change conference in Madrid this week.

In attendance will be heads of state and government, business leaders, scientists and activists.

The Madrid meeting is the last gathering of the COP group before 2020.

The year 2020 is when the Paris agreement comes into effect.

In 2015, nations signed a deal where they agreed that global emissions of greenhouse gases must peak in 2020 at the latest, and then start coming down -- or the world will face disastrous and irreversible damage.

Here's a snippet of the press conference at Lisbon:

Top photos from Getty Images