UNITED NATIONS — Just days after angry youth protests demanding swift action to fight climate change, the United Nations climate summit opened Monday, where dozens of presidents, prime ministers and corporate executives will try to show that they are stepping up action to reduce planet-warming emissions.
No sooner had it begun than the teenage Swedish climate activist Greta Thunberg, her voice quavering like it rarely does, lit into them, excoriating world leaders for their “business as usual” approach to bringing down greenhouse gas emissions at a time when temperatures are swiftly rising. “The eyes of all future generations are upon you,” she said, reading from prepared remarks. “If you choose to fail us, I say we will never forgive you.”
India’s prime minister, Narendra Modi, said his country would increase its share of renewable energy by 2022, without making any promises to reduce its dependence on coal. Chancellor Angela Merkel of Germany promoted a new plan worth $60 billion over 10 years to speed a transition to clean power. Britain, Norway, Costa Rica and 12 other countries will promise to achieve net-zero emissions by 2050. And by the end of the day, expect to see a signal of how much other countries are willing to do in the face of inaction by the United States, which is responsible for the largest share of greenhouse gas emissions since the industrial age.
Late morning, President Trump unexpectedly dropped into the General Assembly hall with Vice President Mike Pence. Michael R. Bloomberg, the former New York City mayor, welcomed Mr. Trump’s presence at the United Nations and drew applause when he addressed the president directly by saying, “Hopefully our discussions here will be useful for you when you formulate climate policy.”
In this body of nations, some of the most notable pledges are expected to come from cities and private companies, including banks, large asset funds, and shipping firms. All eyes were on whether China, currently the world’s largest emitter of greenhouses gases, would signal higher ambition. A special representative of Chinese President Xi Jinping was scheduled to speak later in the morning.
The gap between the incremental promises being made in the hall and the dramatic effects of climate change could not be more stark.
The world is getting hotter, faster, the World Meteorological Organization concluded in its latest report Sunday, with the five-year period between 2014 and 2019 the warmest on record. Emissions of carbon dioxide, a major contributor to global warming when it is pumped into the atmosphere, are at all-time highs. The seas are rising rapidly. The average global temperature is 1.1 degrees Celsius higher than what it was in the mid-19th century, and at the current pace, average global temperatures will be 3 degrees Celsius higher by the end of the century.
“I will not be there, but my granddaughters will, and your grandchildren, too,” the United Nations secretary general, António Guterres, told those assembled inside the General Assembly hall. “I refuse to be an accomplice in the destruction of their one and only home.”
The president of Chile, Sebastián Piñera, said 30 countries had pledged to reach net-zero emissions by 2050. The pledges are seen as critical to reinforcing the Paris Agreement, a pact among nations to jointly fight climate change, at a time when the United States government has said it will withdraw from the agreement and has all but abandoned the global effort to reduce greenhouse gases and help the world’s most vulnerable countries cope with the consequences of a warming world.
Mr. Guterres’ most direct call went to those countries that use money from their taxpayers to subsidize fossil fuel projects that, as he put it, “boost hurricanes, spread tropical diseases and heighten conflict.”
“We are in a deep climate hole. To get out, we must first stop digging,” he said. “Is it common sense to build ever more coal plants that are choking our future? Is it common sense to reward pollution that kills millions with dirty air and makes it dangerous for people in cities around the world to sometimes even venture out of their homes?”
President Trump had planned to be in New York on Monday but hadn’t been expected to attend Monday’s summit. Instead, the administration sent a State Department official who did not request a speaking slot. The administration has rolled back efforts to cut emissions from automobile tailpipes, coal plants and oil and gas wells. Several United States governors were present and expected to announce stepped-up goals on reducing their own emissions.
Other major emitters not speaking at the Monday summit are Australia, Saudi Arabia, Japan and Brazil. The Secretary General had said that only those who were ready to announce concrete new steps would be given speaking time.
Their absence underscored a growing global tension over the push to phase out coal, oil and gas.
The pledges being delivered against the United Nation’s green marbled backdrop stood in sharp contrast to the anger that spilled onto the streets Friday, when masses of children and young people protested around the world demanding a swift pivot away from the world’s fossil fuel-based economy. On Monday, young people blocked traffic in Washington to demand a swift pivot away from the world’s fossil fuel-based economy.
“Friday landed a big emotional punch,” said Rachel Kyte, a special representative on sustainable energy for the United Nations secretary general.
“From this summit, we need to ratchet up action and ambition and get to a point where every country has got a plan that makes sense and is consistent,” she said. “We’re not there yet.”
Scientists have warned that severe droughts, escalating wildfires and rising seas fueled by climate change threaten to tear apart ecosystems and economies, undermining decades of progress in global health and poverty reduction.
“Speeches don’t match the moment,” President Sauli Niinisto of Finland said. “If we all don’t do more, more people will suffer.”
Some analysts said they hoped Chinese leaders at the meeting would announce that their country’s emissions will peak earlier than they had pledged under the Paris Agreement, though others said that was unlikely. Though China today produces more greenhouse gas emissions than any other country, but it is on track to meet the relatively modest goals it set for itself under the Paris climate agreement.
“China is going to do a really good job of saying all the right things but we will have a very difficult time identifying the actions that are going to support that,” said Taiya Smith, director of the China program for the Climate Leadership Council, a conservative group that has called for carbon-tax policies.
In part, she and others said, that’s a reflection of the overwhelming focus in China on trade relations with the United States, fears about China’s own slowing economy and the failure of the United States, the world’s biggest emitter in historical terms, to act or push other nations to do more under the current administration.
“It’s very unlikely that China will move unless it has to,” Ms. Smith said, adding that, with the United States effectively out of the picture, “All they have to do is show up and they’re the world leader.”
Yet without more ambitious efforts by the United States, China and other big countries to eliminate greenhouse gases, the average temperature globally is on track to rise a dangerous 3 degrees Celsius or more from preindustrial times. According to the United Nations Environment Program, the world’s 20 largest economies, which account for 80 percent of global greenhouse gas emissions, “are not yet taking on transformative climate commitments at the necessary breadth and scale.”
Scientists and policymakers have said that even holding warming to a less-dangerous 1.5 degrees would entail a significant transformation of the global energy system, costing trillions of dollars.
But the cost of doing nothing is also staggeringly high.
Studies show that if emissions continue to rise at their current pace, the number of people needing humanitarian aid as a result of natural disasters could double by 2050. And a sweeping report from 13 United States federal agencies last year warned that failing to rein in warming could shave 10 percent off the country’s economy by century’s end.
For more news on climate and the environment, follow @NYTClimate on Twitter.