Teenage climate change activist Greta Thunberg on Monday opened the United Nations Climate Action Summit with an angry condemnation of world leaders for failing to take strong measures to combat climate change — "How dare you," she said.

Days after millions of young people took to the streets worldwide to demand emergency action on climate change, leaders gathered for the annual United Nations General Assembly aiming to inject fresh momentum into stalling efforts to curb carbon emissions.

A visibly emotional Thunberg, 16, said in stern remarks at the opening of the summit that the generations that have polluted the most have burdened her and her generation with the extreme impacts of climate change.