United Nations – An emotional Greta Thunberg tore into world leaders at a UN climate summit on Monday, accusing them of betraying her generation by failing to tackle greenhouse gas emissions, as announcements by major economies fell far short of expectations.The Swedish teen's impassioned speech, in which she repeated the words "How dare you" four times, was the defining moment of the meeting, called by UN chief Antonio Guterres to reinvigorate the faltering Paris climate agreement.Ahead of the conference, the United Nations issued a release saying 66 countries vowed to achieve carbon neutrality by 2050, along with 10 regions, 102 cities, and scores of businesses.But pre-summit predictions of new, headline-grabbing commitments, particularly by the likes of China and India, failed to match reality, angering environmental groups.The world's top scientists believe long-term temperature rise must be limited to 1.5 degrees Celsius over pre-industrial levels to prevent runaway warming with catastrophic effects.But rather than peaking, the level of emissions being released into the atmosphere are at an all-time high, triggering global weather hazards from heatwaves to intense hurricanes and raging wildfires.New data released on Monday showed the 2019 Arctic sea ice minimum is ranked at second-lowest in the 41-year satellite record, effectively tied with 2007 and 2016.Unanimous disappointment"I shouldn't be up here. I should be back at school on the other side of the ocean," said Thunberg, 16, who has become the global face of a growing youth movement against climate inaction that mobilised millions in a worldwide strike on Friday."You come to us young people for hope. How dare you?" she thundered, her voice at times breaking with emotion.Matters did not improve much as a succession of national leaders took to the podium saying they understood the gravity of the situation but then failing to announce concrete plans.Indian Prime Minister Narendra Modi did not say explicitly whether his country would enhance its commitments made under the Paris agreement – though he did say it was working on more than doubling its renewable energy capacity.There was also no new announcement by China, the world's biggest emitter. Senior foreign policy official Wang Yi spoke instead about the need for multilateralism, taking a veiled swipe at US President Donald Trump for pulling out of the Paris accord on taking office."The withdrawal of certain parties will not shake the collective will of the international community," he said.Environmental and campaign groups reacted with almost unanimous disappointment."I think Greta's impassioned cry for sanity and for actually listening and acting based on the science was ignored," Greenpeace International chief Jennifer Morgan told AFP.Trump surpriseFewer than half of the 136 heads of government or state in New York this week to attend the UN General Assembly attended on Monday.Trump, who announced his intent to withdraw the US from the Paris agreement and has heaped scorn on climate science, had been expected to skip the event but made a brief unscheduled appearance, spending a few minutes in the hall, where he applauded Modi's speech and then left.Among those absent were President Jair Bolsonaro of Brazil, 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.Laurence Tubiana, one of the architects of the Paris agreement, told AFP at the summit that Chinese lack of action was linked to its internal politics as it prepares its next five-year-plan.But she said that she saw progress too."The big win is these groups of countries who are for net zero by 2050," she said."The next step is to have them explain how they do that and what they do immediately."Increased urgencyEarlier, opening the summit, Secretary-General Antonio 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 $500m in extra funds were pledged by major donors.Macron also lauded Russia, which ratified the Paris agreement on Monday, and said Europe must do more, repeating a vow to close coal-fired plants by 2022.Germany's Chancellor Angela Merkel, repeated recently announced pledges including $55bn for a new innovation and technology package and net zero emissions by 2050.British Prime Minister Boris Johnson announced the UK would double its climate change funding through an overseas development programme to $14.4bn over five years.In his closing comments, Guterres emphasised the positives, highlighting the growing action from the corporate sector, commitments from countries to plant more than 11 billion trees.But he added: "We need more concrete plans, more ambition from more countries and more businesses, saying the next critical landmark would come at a conference in Santiago in December.