Humanity has

Humanity has "opened the gates to hell" by allowing the climate crisis to worsen, the secretary general of the United Nations has warned at a climate summit of leaders that saw angry denunciations of the fossil fuel industry but was undercut by the absence of many of the biggest carbon-emitting countries.

António Guterres opened the UN climate ambition summit, held in New York on Wednesday, with a lacerating attack on wealthy countries and the fossil fuel industry for their ponderous response to the climate crisis.

The UN secretary general said the world is "decades behind" in the transition to clean energy. "We must make up time lost to foot-dragging, arm-twisting and the naked greed of entrenched interests raking in billions from fossil fuels," Guterres said, adding that some fossil fuel companies had embarked upon a "shameful" attempt to stymie the transition.

Wealthy countries need to get their planet-heating emissions to net zero as close as possible to 2040, Guterres said, a task that a recent UN analysis found is well off track, as well as deliver promised climate funding to poorer, vulnerable nations that has so far been lacking.

"Many of the poorest nations have every right to be angry, angry that they are suffering most from a climate crisis they did nothing to create, angry that promised finance hasn't materialized and angry that their borrowing costs are sky high," he said.

Guterres said that "humanity has opened the gates of hell" by unleashing worsening heatwaves, floods and wildfires seen around the world and that a "dangerous and unstable" future of 2.8C global heating, compared with the pre-industrial era, was awaiting without radical action. "The future of humanity is in our hands," he said. "We must turn up the tempo, turn plans into action and turn the tide."

Leaders from more than 100 countries were asked to take part in the climate ambition summit, with invites extended to those the UN deemed "to have new, improved ambition on climate". In a sobering indication of the shortfall in the required effort to avoid disastrous climate change, most of the world's biggest carbon emitters were absent, including Joe Biden, president of the US, and Xi Jinping, president of China - leaders of the two largest polluters.