The COP31 conference is being held in the Turkish resort city of Antalya following a year of deadly climate-related disasters, including heat waves and floods, and another energy shock caused by the Iran war.
"It's a hypocrisy every year that the host countries are given an opportunity to whitewash themselves and we know that these negotiations are filled with lobbyists, paid by the very destructive industries which are benefiting from our extremely violent status quo," Thunberg said as she arrived.
"Our political and economic systems that have become incompatible with human nature."
COP31 co-hosts Turkey and Australia are promoting renewable energy and rooftop solar installations, but both still rely heavily on fossil fuels, especially coal, to generate electricity. Previous hosts, including Brazil, the United Arab Emirates and Azerbaijan, are major oil producers.
Climate change is "threatening everything", Thunberg said, warning that "everything and everyone we love is at stake".
"We should act to protect and benefit people rather than constantly sacrificing the global majority and the very planet we are all living on, for a fortunate few to keep making unimaginable profits and maintaining geopolitical power," she said.
This is the first climate summit Thunberg has attended since the 2021 talks in Glasgow, Scotland, where she dismissed world leaders' promises as "blah, blah, blah".
She rose to prominence in 2018 when, aged 15, she began a solitary " School Strike for Climate " outside the Swedish Parliament. In 2022, she published The Climate Book, outlining actions to address the climate crisis.
A key goal for Turkey is global electrification: shifting sectors such as transportation, buildings and heavy industry away from fossil fuels and toward electricity. Turkey wants electricity, preferably generated from renewable sources such as solar and wind, to account for 35 per cent of global energy consumption by 2035, up from 23 per cent today.
"We have to take the victories we have, of course, because we are so desperate in this situation that we have to take all the positive signs we can get to save as much as we can still save," said Thunberg, who is expected to spend several days at COP31.
The UN talks in Antalya run until November 20.
