Environmental activist Greta Tonberg inaugurated the United Nations Climate Action Summit on Friday, with strong criticism of world leaders for failing to take strong action to combat climate change, telling them: "You stole my dreams."

Days after millions of young people took to the streets in cities around the world to demand urgent action on climate change, world leaders met to attend the annual meetings of the UN General Assembly, in a bid to give new impetus to stalled efforts to reduce carbon emissions.

"The generations that have polluted the world the most are their campaign and generation the burden of the extreme effects of climate change," said 16-year-old Tonberg, clearly influenced by the opening speech of the summit. "The whole thing is wrong. I shouldn't have been here. I have to go back to school on the other side of the ocean as all of you come to us with hope, how dare you?" "You stole my dreams and my childhood with your empty words," she said, saying the plans the leaders would unveil would not be enough to respond to global warming.

Tonberg began to miss school on Fridays a year ago to protest outside the Swedish parliament, creating a global climate movement known as "Fridays for the Future." US President Donald Trump briefly appeared at the summit with Vice President Mike Pence and Secretary of State Mike Pompeo. He made no comments, but listened to German Chancellor Angela Merkel and Indian Prime Minister Narendra Modi. Trump is a climate change denier and has retracted all relevant US legislation to combat it. Former New York Mayor Michael Bloomberg, now the UN special envoy for climate action, criticized Trump's flashy appearance before speaking, amid laughter: "We hope our deliberations will be useful to you as you shape climate policy."

Merkel announced that Germany would double its contributions to a UN fund to support developing countries to combat climate change, to 4 billion euros from the current 2 billion dollars.