A tearful address by Greta Thunberg dominated the UN's Climate Action Summit on Monday, where the teenager accused world leaders of betraying her generation by failing to tackle greenhouse gas emissions and asked them "How dare you?"
The Swedish climate activist's remarks came after calls from UN Secretary General Antonio Guterres to reinvigorate the faltering Paris Climate Accord, which 66 countries have responded to with vows to achieve carbon neutrality by 2050.
The summit, the UN's headline event at the opening of the world body's 74th General Assembly, comes as mankind is releasing more emissions into the atmosphere than at any point in history, triggering global weather hazards from heatwaves to intense hurricanes, raging wildfires and acidifying oceans.
Yet the gap between carbon reduction targets demanded by scientists to avert catastrophe and actions thus far taken is only widening.
“I shouldn't be up here. I should be back at school on the other side of the ocean,” said Ms Thunberg, 16, who has become the face of a global growing youth movement against climate inaction that mobilised an estimated four million protesters in a worldwide strike on Friday.
“You come to us young people for hope. How dare you?” she said, her voice breaking with emotion.
“We are in the beginning of a mass extinction, and all you can talk about is the money and fairy tales of eternal economic growth. How dare you?”
In a surprise turn of events, US President Donald Trump, a climate-science sceptic, made a brief unscheduled appearance at the summit, which he had been expected to avoid entirely.
Having repeatedly expressed doubt about the overwhelming scientific consensus on man-made causes of global warming, Mr Trump spent 10 minutes in the hall, where former New York mayor Michael Bloomberg addressed the president and suggested he might learn something.
“Hopefully our discussion will be useful to you when you formulate climate policy,” Mr Bloomberg said, announcing that he was donating millions to an initiative to help persuade countries against building coal-fired power plants, an energy source Mr Trump has lauded.
Mr Trump applauded a speech by Indian Prime Minister Narendra Modi, whose solar initiatives have been welcomed by the UN, and then left.
The UN estimates that the world needs to increase its current efforts five-fold to contain climate change. Countries announced commitments to carbon reduction targets under the Paris Agreement of 2015, and are now expected to update their "nationally determined contributions" by 2020.
Opening the summit, Mr Guterres said: "The climate emergency is a race we are losing, but it is a race we can win."
French President Emmanuel Macron invited his counterparts from Chile, Colombia and Bolivia to a meeting where $500 million (Dh1.8bn) in extra funds were pledged by the World Bank, Inter-American Development Bank, and non-profit Conservation International to protect the world's rainforests.
But fewer than half the 136 heads of government or state in New York this week to attend the UN General Assembly were present.
Among those who stayed away were Brazil's President Jair Bolsonaro, under whose leadership the Amazon rainforest is continuing to burn at record rates, and Australian Prime Minister Scott Morrison whose government has pursued an aggressively pro-coal agenda.
China, the world's biggest carbon emitter by far but also a leader in renewables, was represented by Foreign Minister Wang Yi who called on developed countries to lead by example in reducing emissions — but also said China was respecting its climate change promises.
In his speech, Mr Macron made a clear reference to Ms Thunberg and the other young speakers who preceded him. “No official can remain deaf to this demand for intergenerational justice,” he said.
“We need this youth to help us change things … and put more pressure on those who do not want to move.”
He also praised Russia, which ratified the Paris Agreement on Monday, and said Europe must do more, repeating a vow to close coal-fired plants by 2022.
German Chancellor Angela Merkel, who has been criticised by activists for not doing enough, said it was her government's responsibility to “take everyone along with them”, including those who doubt climate change.
Mr Guterres has asked countries to bring “concrete, realistic plans” to enhance the commitments made in Paris towards the goal of limiting long-term warming to less than 2°C Celsius — and ideally 1.5°C — over pre-industrial levels by the year 2100.
These are deemed important to avoid hitting a number of so-called "tipping points", such as the melting of polar permafrost, that could trigger irreversible warming and fundamentally alter weather events and ecosystems.
But officials have been careful to manage expectations and say Monday's summit is also a run-up event to the 2020 UN climate summit that Britain will host in Glasgow.