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.

Also absent was France's Emmanuel Macron, India's Narendra Modi and Britain's Rishi Sunak, who has been the focus of intense criticism after he announced a watering down of the UK's policies to reach net zero emissions. "Their absence is illustrative of the point we aren't taking seriously the magnitude of the task right now," said Kelly Sims Gallagher, dean of the Fletcher School at Tufts University and a former White House adviser. "If we were serious, all of them would be at the table today. It's concerning."

The summit itself contained some fiery denunciations of the fossil fuel industry, a stark contrast to previous diplomatic niceties that muted such criticism in previous UN forums. There was applause in the room when Gavin Newsom, the governor of California, said that "this climate crisis is a fossil fuel crisis".

"It's not complicated. It's the burning of oil. It's the burning of gas. It's the burning of coal. And we need to call that out," Newsom said. "For decades and decades, the oil industry has been playing each and every one of us in this room for fools. They have been buying off politicians. Their deceit and denial going back decades, have created the conditions that persist here today."

Gabriel Boric, the president of Chile said that "we need to leave fossil fuels behind" and criticized "greenwashing" by large businesses, while Kausea Natano, prime minister of Tuvalu, a Pacific island nation at acute risk from sea level rise, called for a fossil fuel non-proliferation treaty. "The longer we remain addicted to fossil fuels, the longer we commit ourselves to mutual decline," he said.

Some other developing and small island state leaders also lamented the lack of progress by wealthy nations to deliver $100bn in promised climate aid and the difficulties in securing financing at reasonable rates in order to build out the infrastructure needed to adapt to a world with fiercer storms, heatwaves and floods.

"We are in the final stages of the actions needed to preserve this planet and regrettably I don't think everyone is getting it," said Mia Mottley, prime minister of Barbados.

"It's painful to continue to see that you are asking us to increase borrowing to build resilient infrastructure for something we didn't do, and at the same time you want to also ensure you have a loss and damage fund that doesn't have the adequate means for grant funding to help countries rebuild. It's unconscionable and almost a crime against humanity."

Guterres admitted that the summit alone was not likely to significantly alter the trajectory of the climate crisis but some measures were announced in New York, such as the US being one of a host of countries to sign a treaty to protect the world's oceans. Michael Bloomberg, the billionaire former mayor of New York, meanwhile pledged another $500m to an effort to shut down coal and gas plants in the US.

But there remains a yawning gap in terms of what is needed to avert disastrous climate change, with little optimism the upcoming Cop28 climate summit in Dubai in November will remedy this.

"The small steps countries offered are welcome, but they're like trying to put out an inferno with a leaking hose," said David Waskow, director of the International Climate Initiative at the World Resources Institute. "There is simply a huge mismatch between the depth of actions governments and businesses are taking and the transformative shifts that are needed to address the climate crisis."