Ms Thunberg has been highly critical of the Cop26 talks that are beginning their second and final week, with countries under pressure to increase action to cut emissions to avoid dangerous warming and provide finance for poorer nations to cope with climate impacts.
The 18-year-old activist, who inspired the youth climate strike movement with her one-person school protest starting in 2018, was not invited to formally address the Cop26 conference.
She told young protesters at a march on Friday that the UN talks were “now a global north greenwash festival, a two-week long celebration of business as usual and blah blah blah” and branded it a failure.
It is understood she left Glasgow at the weekend and travelled by train back to Stockholm.
Ms Thunberg was off school last week due to the autumn break and had decided to attend only the first week of the Cop26 conference to avoid missing too many days of school.
During her time in Glasgow she met a number of leading figures, attended several rallies and spent time with First Minister Nicola Sturgeon.
She turned the air blue at a rally in the city’s Festival Park across the River Clyde in Govan.
Addressing a mainly youthful audience while the summit continues at the SEC, said: “Inside COP they are just politicians and people in power pretending to take our future seriously. We say, ‘No more blah blah blah, no more exploitation of people and nature and the planet.”
“No more whatever the f*** they’re doing inside there’.”