After three weeks of sailing across the Atlantic Ocean to attend the United Nations Climate Change Conference in Spain, teen climate activist Greta Thunberg arrived Tuesday in neighboring Portugal, where she was welcomed by an enthusiastic crowd of supporters.\u0022We\u0026#039;ve all been on quite an adventure,\u0022 the 16-year-old Swede told reporters in Lisbon shortly after her arrival. Thunberg has gained global recognition for her solitary protests for climate action outside the Swedish Parliament last year, which led to an international youth-led school strike movement known as Fridays for Future.Climate change activist Greta Thunberg arrived in Lisbon, Portugal, on Tuesday after a 3-week journey across the Atlantic. Thunberg will head to a UN climate change conference in Madrid, Spain. pic.twitter.com/yDpcTPMBzs— NBC News (@NBCNews) December 3, 2019In August, Thunberg—who refuses to travel by plane—sailed from the United Kingdom to the United States for a U.N. summit in New York City. She also toured North America, addressing members of the U.S. Congress, joining major protests, and meeting with climate activists. After the U.N. conference, COP 25, was moved from Chile to Spain, she turned to social media to find a low-carbon way to get to Madrid.Thunberg\u0026#039;s call for travel assistance was answered by the owners and crew of La Vagabonde, a white 48-foot catamaran that uses solar panels and hydro-generators for power. The teenager and her father Svante joined professional sailor Nikki Henderson as well as yacht owners Riley Whitelum and Elayna Carausu and their baby for the three-week journey.\u0022I\u0026#039;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.\u0022—Greta Thunberg, climate activist\u0022I am not traveling like this because I want everyone to do so,\u0022 Thunberg explained to reporters Tuesday. \u0022I\u0026#039;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.\u0022The Associated Press reported that Thunberg will spend several days in the Portuguese capital before she heads to COP 25, where representatives from governments across the globe are discussing efforts to battle the climate crisis, including national commitments under the 2015 Paris agreement.At the conference, Thunberg said, \u0022we will continue the fight there to make sure that within those walls the voices of the people are being heard.\u0022\u0022I think people are underestimating the force of angry kids,\u0022 she added. \u0022If they want us to stop being angry, then maybe they should stop making us angry.\u0022Ahead of the conference, which kicked off Monday and is scheduled to run through Dec. 13, youth leaders organized a worldwide climate strike on Friday to pressure the COP 25 attendees to pursue more ambitious policies. Another global strike is planned for this coming Friday.Chilean Environment Minister Carolina Schmidt—who is still serving as president of COP 25, despite the relocation—said Tuesday that she hopes Thunberg will motivate those attending the conference to back bolder climate commitments.Schmidt told the AP that Thunberg \u0022has been a leader that has been able to move and open hearts for many young people and many people all over the world.\u0022\u0022We need that tremendous force in order to increase climate action,\u0022 the minister told Reuters television. \u0022We need Greta in here with all that force.\u0022Bolstering arguments from both activists and policymakers that the international community needs to step up its efforts to address the climate crisis, the World Meteorological Organization on Tuesday released a new report which warned that inadequate efforts to curb planet-warming emissions could lead to a global temperature rise of 5°C by the end of the century.