“It feels like we have passed some kind of social tipping point where people are starting to realise that we cannot keep looking away from these things,” the 17-year-old said in an interview with the BBC.
“We cannot keep sweeping these things under the carpet, these injustices.” Thunberg's interview aired as global capitals braced for another weekend of anti-racism protests triggered by the death of African American George Floyd at the hands of a white policeman.
British protesters have toppled the statue of a 17th century slave trader and the Church of England and the Bank of England have expressed remorse for profiting from the sale of Africans to the Americas.
A statue of a southern general who defended slavery during the US Civil War was pulled down and set on fire by protesters in Washington on Friday.
Thunberg said “people are starting to find their voice, to sort of understand that they can actually have an impact”.
She also described being stunned by the depth of US poverty she discovered while travelling with her father in an electric car they borrowed from the former California governor and actor Arnold Schwarzenegger.
“It was very shocking to hear people talk about that they can't afford to put food on the table,” she said.
US demonstrations this weekend follow the Juneteenth holiday on Friday that commemorates the emancipation of those who had been enslaved there.
Hundreds gathered in London's Hyde Park and marched past landmarks such as Buckingham Palace and Big Ben on Saturday while police watched from a distance.
The mood was more festive and crowds much smaller and than at demonstrations during which dozens were arrested in London over the previous two weekends.
“This protest makes me feel hopeful but it also concerns me,” a marcher who identified herself as Tash told Britain's Press Association.
“We're in a pandemic and I don't want it to just be a hashtag and a trend,” the 23-year-old said.
“It is hopeful because people are finally listening but are they just listening because they have the time and they are bored?” she asked.
A few hundred people also took a knee to honour Floyd on a central square in the Scottish capital Edinburgh.