She went on to criticise world leaders, saying too much responsibility was being placed on children to raise awareness of the climate crisis.
Thunberg said that the Covid-19 crisis had shown that world leaders were incapable of dealing with two emergencies at once, and said that climate change should be treated with urgency.
Thunberg appeared by video link at the Venice film festival where the film, I Am Greta, has been screened.
The Swedish activist Greta Thunberg has called for more action to be taken to address the climate crisis, which she says has slipped dangerously off the political agenda.