"She is making a statement that you don't always have to take the easy way", said Belgian climate activist, Lander Wanters. "And eventually we will be going to COP25 and we will continue the fight there to make sure that within those walls, the voices of the people are being heard".
She along with British navigator Nikki Henderson and the Australian family who own the vessel were expected to arrive in Portugal's capital Lisbon this morning after a voyage of more than 5,500km.
Ms Thunberg rose to prominence after she started spending her Fridays outside Sweden's parliament in August 2018, holding a sign reading "school strike for climate".
Thunberg set sail from NY after touring North America, raising awareness about climate change.
The 16-year-old climate activist has spent more than 2 weeks crossing the ocean on a catamaran from NY, confirming her commitment to a low-emission lifestyle.
Her trip contrasted with the many air miles flown by most of the United Nations meeting's 25,000 attendees.
In September, Thunberg addressed the U.N. General Assembly in NY to berate world leaders, accusing them of having "stolen my dreams and my childhood".
The yacht, named La Vagabonde, leaves little or no carbon footprint when its sails are up, using solar panels and hydro-generators for electricity.
Portuguese President Marcelo Rebelo de Sousa said it was a "great pleasure" to have her in Lisbon but did not feel it was his place to personally greet the activist.
She said: 'This year, we have seen accelerating climate change impacts, including increased droughts, storms and heatwaves, with dire consequences for poverty eradication, human health, migration and inequality.
"This is all wrong", Thunberg stated as she addressed the assembly.
The World Meteorological Organization said Tuesday that preliminary temperature data show the years from 2015 to 2019 and from 2010 to 2019 "are, respectively, nearly certain to be the warmest five-year period and decade on record".
Meanwhile, a report by the United Nations weather agency released on the sidelines of the climate talks found that the current decade is likely to set a new ten-year temperature record.
"Since the 1980s, each successive decade has been warmer than the last", the agency said.
The World Meteorological Organisation (WMO) launched a report at the summit on Tuesday (local time) that found the past decade was nearly certain to have been the hottest on record.
Thunberg's arrival in Lisbon coincides with the release of a bleak report by the Geneva-based World Meteorological Organization.