U.N. General Assembly: U.N. Live Updates: General Assembly Opens Amid War and Global Turmoil

But many problems are yet to be solved.

In the Gaza Strip, a cease-fire with Hamas remains elusive after more than 11 months of fighting. The escalating cross-border volleys of missiles by Israel and Hezbollah poses the threat of a multifront war in the Middle East. The war between Russia and Ukraine is dragging into its third year with no end in sight.

Aides say Mr. Biden, who arrived in New York on Monday evening, will also use his speech to address the climate crisis and the environment; the need to strengthen systems for providing humanitarian assistance to strife-torn corners of the world; and the implications of new technologies such as artificial intelligence.

The speech will also be a farewell of sorts. Mr. Biden believes deeply in the power of personal relationships as an instrument of diplomacy, and aides say he is likely to have a number of one-on-one meetings with fellow world leaders on the sidelines of the summit. His address is not expected to be a political one, but it does occur in a political context, at a moment of great uncertainty about America’s future role in the world.

The speeches begin at 9 a.m. Eastern, with Secretary General António Guterres giving the first, followed by President Luiz Inácio Lula da Silva of Brazil — whose leader has been the first to speak at the session since the U.N.’s founding — and then Mr. Biden. The New York Times will stream Mr. Biden’s address live.

Here’s what else to know:

• A proposal for Ukraine: The U.N. Security Council will convene a session Tuesday on Ukraine, a last-minute addition after Ukrainian diplomats raised concerns that their war might be falling off the agenda with so much attention fixed on the Middle East. President Volodymyr Zelensky of Ukraine is expected to share a new peace proposal and an appeal for more military support to launch strikes deeper into Russia, Security Council diplomats said. He is scheduled to address the 193-member General Assembly on Wednesday.

• Secretary general’s address: Mr. Guterres is expected to urge modernization of U.N. institutions like the Security Council and the World Bank. “Our world is going through a time of turbulence and a period of transition,” Mr. Guterres said on Sunday at a conference he hosted ahead of the General Assembly. “But we cannot wait for perfect conditions. We must take the first decisive steps toward updating and reforming international cooperation to make it more networked, fair and inclusive — now.”

• Who else is speaking: Other speakers on Tuesday include President Masoud Pezeshkian of Iran; President Recep Tayyip Erdogan of Turkey; King Abdullah II of Jordan; and the leaders of Qatar, Poland and Argentina.

• Who won’t be there: The recent escalation of attacks between Israel and Hezbollah, the armed Iranian-backed Lebanese group, prompted Prime Minister Najib Mikati of Lebanon to cancel his appearance. Israel’s prime minister, Benjamin Netanyahu, delayed his trip until Wednesday. He is scheduled to speak on Thursday.

With his recent public messaging, Mr. Zelensky is well on his way to succeeding with what is likely his most achievable goal for his U.S. visit: trying to regain attention for a war that in its third year has been overshadowed by the conflict in Gaza.

“One of his main goals is to try to put the Ukraine war back on the global agenda” and the minds of policymakers in Washington and in Europe, said Max Bergmann, the director of the Europe, Russia and Eurasia program at the Center for Strategic and International Studies.

He said Mr. Zelensky also wants to convince developing countries that have been neutral on the war to support Ukraine, a prospect that seems unlikely, given that they haven’t publicly backed Ukraine so far. “He sees an opportunity at the U.N. to put some international pressure on Russia as well,” Mr. Bergmann added.

This week, Mr. Zelensky will be pushing for all possible military aid, a shift in international thinking that says Russia cannot be defeated and long-term security guarantees to ensure support for Ukraine if Donald J. Trump, who has long been skeptical of U.S. involvement in the war, is elected in November.

In a speech Sunday, Mr. Zelensky foreshadowed his victory plan to end hostilities.

Mr. Zelensky said he would ask for “weapons to defend our independence and our people; diplomacy to consolidate partners and force Russia into peace; and justice so that Russia is held accountable for this war and feels its consequences.”

This visit comes at a crucial point in the war, with Ukraine on the defensive, despite a bold incursion into Russia’s Kursk territory this summer. Russian troops have made significant inroads in the east of the country, destroying Ukrainian villages as they churn forward, foot by foot, now occupying more than 18 percent of the country. Russia has more ammunition, more troops and more potential troops than Ukraine.

In a meeting with journalists Friday in Kyiv, Mr. Zelensky said he planned to use his visit to ask for more weapons and permission to strike inside Russia. All summer, Ukraine has pleaded to use Western-supplied long-range missiles to strike targets deep in Russia. Western leaders have been reluctant, fearful that could lead to an escalation with Russia, a nuclear power.

Analysts said they believe that Western leaders may relent and grant at least limited permission to use those weapons, especially after the Kursk offensive, which, despite using Western-supplied equipment inside Russian territory, didn’t lead to an escalation of the war.

Mr. Zelensky is also expected to argue that Ukraine should be invited into the North Atlantic Treaty Organization, and to try to build an amicable relationship with the next U.S. president in the hopes that they will not just match Mr. Biden’s commitment to Ukraine but increase it.

Mr. Zelensky plans to meet Thursday with Vice President Kamala Harris, the Democratic candidate for president. He then hopes to meet Thursday or Friday with Mr. Trump, who has said that he will “probably” meet with the Ukrainian president. A spokesman for Mr. Trump said on Monday that he had nothing to announce.

Analysts said it’s unlikely that Ukraine will be invited into NATO at this point, or that Western countries will commit more resources to the war.

Ian Bremmer, the president and founder of the Eurasia Group, a political risk consulting organization, said Mr. Zelensky “probably already received the peak of the economic and military support that he can get from the West.” He added that it was tough to defend the existing levels of spending, given fiscal and political challenges. “Nobody thinks that a victory plan is going to move the needle, particularly at this point.”

But all around Mr. Biden, there are problems yet to be solved. In Gaza, a cease-fire between Israel and Hamas remains elusive after 11 months of fighting. The escalating volley of missiles across the Israel-Lebanon border poses the threat of a multifront war in the Middle East. The war between Russia and Ukraine is dragging deep into its third year with no end in sight.

“America’s back, all right — he can make that case — but with severe limitations on its capacity to lead,” said Aaron David Miller, a longtime Middle East peace negotiator who has advised presidents of both parties. “Biden’s administration is a cautionary tale, I think, of just how complicated and surprising the international environment is, and the limitations of American power.”

White House officials, speaking anonymously on Monday evening to preview Mr. Biden’s remarks, offered few specifics. They said he would use his speech to talk about an array of issues, including about the climate crisis and the environment; the need to strengthen systems for providing humanitarian assistance to strife-torn areas like Gaza, Ukraine and Sudan; and the implications of new technologies such as artificial intelligence.

Mr. Biden, who arrived in New York on Monday evening, will also meet on Tuesday with the secretary general of the United Nations, António Guterres, to discuss efforts between the U.N. and the United States to advance peace, safeguard human rights and help countries develop. And he will host a meeting of a coalition to address the global opioid crisis.

Aides say Mr. Biden is likely to have a number of one-on-one meetings with fellow world leaders on the sidelines of the summit, a key tool for a president who has long believed deeply in the power of personal relationships as an instrument of diplomacy. On Wednesday, White House officials said, Mr. Biden will meet with the new president of Vietnam. On Wednesday evening, he will host world leaders and senior U.N. officials for a reception at the Metropolitan Museum of Art.

But the speech to his fellow world leaders on Tuesday morning will be the centerpiece of his U.N. visit, and will be a farewell of sorts. Mr. Biden has spent more than 50 years on the world stage — as a senator, including a stint as the chairman of the Foreign Relations Committee, as vice president and as president.

“This is somebody who, for decades, has felt like he was operating at the highest levels, talking with leaders all over the world, defending and advancing American interests,” said Jon B. Alterman, the director of the Middle East program at the Center for Strategic and International Studies in Washington. “This is the valedictory for that.”

Mr. Biden’s speech is not expected to be a political one, but it does occur in a political context, at a moment of great uncertainty about America’s future role in the world. If Vice President Kamala Harris wins the presidential election in November, her foreign policy is likely to mirror Mr. Biden’s own view of American engagement in the world. If former President Donald J. Trump wins, it will mark a return to his isolationist stance; Mr. Trump has little use for global institutions like the United Nations.

With that in mind, White House officials said, Mr. Biden will also use the speech to make the case for strengthening the United Nations and for overhauling and expanding the U.N. Security Council. Still, there is only so much the president can do in the four months he has left in office.

“As he looks out at this world, what he sees is — take your pick — either migraine headaches or root canal operations,” said Mr. Miller, the Middle East peace negotiator. “There’s not a single problem out there that has comprehensive solutions, so it’s all about managing a world that is not transformable — and I think that is a far cry from where he was in January of 2021, and the expectations that the world had for Joe Biden.”

She has often considered moving but then changed her mind once the chaos subsided. “It’s just one week, but it’s a very intense week,” Ms. Flores, 52, said.

The 79th session of the General Assembly will convene on Tuesday, and for the rest of the week Manhattan’s East Side will host more than 100 heads of state and dignitaries. That role is more of a headache than an honor for many New Yorkers who live or work in the neighborhood.

The city’s Department of Transportation designated the week as one of the year’s worst for traffic congestion. Street closures, security protocols and protests will snarl vehicles up and down Manhattan. At a news conference on Friday, Philip Rivera, the chief of the Police Department’s Transportation Bureau, urged commuters to find other ways to get around, like walking, biking or taking public transportation.

Chief Rivera said road closures began earlier than usual this year to accommodate Summit of the Future, one of several events that are part of the U.N.’s “High-Level Week.” The summit, where leaders discussed sustainable development goals, ran from Sunday to Monday.

Allison Arthur May, 50, lives on East 44th Street, one of several that will be closed to traffic between First and Second Avenues until the General Assembly concludes, according to the police.

Ms. Arthur May said she typically used Citi Bike but that even that could be tricky during High-Level Week, when she has to navigate unusual traffic patterns and quick-moving motorcades.

“Heads of state don’t follow any traffic rules,” she said.

For people who have no choice but to drive, like Ibrar Tipu, a taxi driver, the road closures and gridlock in Manhattan will be an unavoidable pain. Even late last week, he said, traffic was growing worse in the area — and drivers were behaving aggressively.

“I have seen at least eight or nine accidents over the last month,” he said.

World leaders began arriving in New York over the weekend, before the most closely watched part of the week, the general debate, which begins Tuesday and concludes next Monday.

President Biden will be among the first speakers to address the assembly on Tuesday. He will participate in the proceedings Monday through Wednesday, according to the White House.

Beyond the U.N. headquarters, organizations are planning events across New York to coincide with High-Level Week. Bloomberg Philanthropies, for one, will hold its Global Business Forum on Tuesday at the Plaza Hotel. Climate Group, an international nonprofit, will host events over several days as part of its annual Climate Week.

Though some parts of High-Level Week stay the same each year, Ms. Flores said the level of security could vary depending on the political situation.

“This year I expect to be insane,” she said.

John Chell, the Police Department’s chief of patrol, said at the Friday news conference that the department was anticipating significant protests this year. Since last October, Mr. Chell said, the department has responded to more than 4,000 demonstrations, many of them protesting Israel’s military offensive in Gaza.

“That changes the dynamic of the U.N. General Assembly,” Chief Chell said. “But we’ve been handling this every day, about 12 protests a day. We will keep people safe.”

New York’s interim police commissioner, Thomas G. Donlon, said at the news conference that the department was working with federal and international agencies, including the Secret Service and the Diplomatic Security Service, to make sure the week ran smoothly.

For New Yorkers who work at businesses near the United Nations building, the week isn’t all bad. Business booms, though the rush can be stressful.

Azmat Reheat, the owner of a nearby drugstore, said dignitaries and their aides visit in search of essentials, like vitamins, bobby pins, slippers and facial products.

“Everybody stops by,” he said. “Every kind of person on earth. It gets busy.”

Juana Rivera, who works at a dry cleaner a few blocks away from United Nations Plaza, said the conference meant fast turnarounds, many more deliveries and late hours.

“I’m not exactly looking forward to it, but it’s good for business,” she said.

The one exception to the rush will be the area’s food trucks. Ahmed Mostaque, who has run a halal cart in the neighborhood for almost 15 years, said that business had ramped up before Saturday but that the carts were then required to clear out for the next 10 days. Another cart worker, Ahmed Badawi, said that while profits might suffer, he didn’t mind being forced to take time off.

“It’s crazy now,” he said. “But soon, I’ll get to sleep.”

Mr. Biden even held on to hope for the transformative peace deal for the Middle East that he thought was within grasp a year ago, believing it could survive even as the war between Hamas and Israel tore at its foundations.

Now, Mr. Biden’s aides say, the president is beginning to acknowledge that he is simply running out of time. With only four months left in office, the chances of a cease-fire and hostage deal with Hamas look dimmer than at any time since Mr. Biden laid out a plan at the beginning of the summer. And the risk of a wider war has never looked greater.

In public, at least, administration officials insist they have not given up. They say they simply cannot move ahead while missiles are bringing death and destruction to northern Israel and southern Lebanon. And they are clinging to the hope that even this level of missile and rocket exchanges between Israel and Hezbollah will not turn into the regional war they have been trying to stave off.

“We could pick any moment, any set of rockets launched by Hezbollah, any set of strikes by Israel, and say, ‘Is this an escalation? Is that an escalation?’” Jake Sullivan, Mr. Biden’s national security adviser, insisted over the weekend. He spoke just hours after Israel killed a Hezbollah leader wanted for his role in two 1983 bombings in Beirut that killed over 350 people, most of them U.S. service members.

“I think it’s not a particularly useful exercise,” Mr. Sullivan continued. “For us, the most useful exercise is to try to drive both parties to a place where we get an agreed and durable outcome that can end the cycle and keep us from ending up in the larger war.”

In many ways, Mr. Sullivan cannot afford to take a different view, at least in public. There is no utility in declaring that Mr. Biden’s plans are shattered for now. While Mr. Sullivan insisted on Saturday that “I do still believe there is a path to get there,” a “winding path, a frustrating path,” many around him think the clock is running out on the president’s plan. In fact, they note, the United States has not even been able to present the “bridging plan” to a final cease-fire — something it said three weeks ago was imminent — because there is no chance either Mr. Netanyahu or Yahya Sinwar, the Hamas leader, will consider it at this time.

“Well, at the moment, we don’t feel like we are in a position, if we put something down today, to get both sides to say yes to it,” Mr. Sullivan said — an understatement, to say the least.

Mr. Biden’s best hope now, in his final months in office, is that his successor will embrace a transformative deal in which Saudi Arabia recognizes Israel, and Israel agrees to the two-state solution that would give Palestinians a true home and a place in the international community.

In private, though, many members of Mr. Biden’s national security team make little effort these days to hide their exasperation with the prime minister. They talk more openly now about the president’s shouting matches in phone calls with Mr. Netanyahu, or Secretary of State Antony J. Blinken’s frustrating visits to Jerusalem in which he got private assurances from the prime minister, only to watch Mr. Netanyahu contradict them hours later.

They now wonder aloud whether the prime minister kept throwing new conditions into cease-fire negotiations in hopes of keeping his fragile coalition together, or to stay in office and out of court.

And while they say he has every right to attack Hezbollah, which has become a “state within a state” in Lebanon, they also say it was telling that the White House announced no phone calls between the president and the prime minister as beepers exploded in the pockets of Hezbollah members and missiles flew. It seemed a sign of how little they had to say to each other.

Dennis B. Ross, the longtime Middle East negotiator, said in an interview on Monday that part of the problem was that Mr. Biden and Mr. Netanyahu had never seen eye-to-eye about their ultimate goals — Mr. Netanyahu’s certainty that he can eradicate every existential threat to his country and Mr. Biden’s determination to bring about the peace deal that has eluded every American president since Richard Nixon.

“Statecraft is all about aligning objectives and means,” said Mr. Ross, now a distinguished fellow at the Washington Institute. “And I don’t see the objectives or the means to achieve them in what Israel is doing now.” Mr. Ross said that Israel’s calculation was that it could force Hezbollah’s longtime leader, Hassan Nasrallah, and his Iranian backers to recognize they will pay a huge price for continuing to attack northern Israel until there is an accommodation with Hamas in Gaza.

Israeli officials counter that their objectives are straightforward: to mount a missile campaign that will wipe out Hezbollah’s command-and-control operations and its stores of weapons. And since last week, when Israel announced that the center of the conflict was moving north, to Lebanon, that process has been a methodical one.

The explosion of pagers and walkie-talkies last week was a start, aimed at not only maiming members of Hezbollah, which the United States designated as a foreign terrorist organization decades ago, but also at making them fearful of communicating with one another. It was a plan that was years in the making, involving front companies that got deeply into Hezbollah’s supply chain. The fact that Israel’s leadership chose to execute it last week was a sign that its broader campaign was about to begin. (Israel has neither confirmed nor denied any role in the explosions.)

Now that campaign has begun. Israeli special forces dropped into Syria, blowing up a facility that is believed to be manufacturing missiles — and supplying Hezbollah. And in Lebanon, Israeli missiles appear to be directed at underground storage tunnels, basements, anyplace where Israeli intelligence believes that tens or hundreds of thousands of weapons are hidden. The number of secondary explosions visible in some video of the attacks suggests that at least some of that intelligence was accurate, American and Israeli officials say.

The scope and scale of the operation suggest that Mr. Netanyahu is no longer satisfied with carrying out periodic brush-backs of Hezbollah’s power. In his view, Oct. 7 changed everything and the time has come to solve the problem once and for all — both in Gaza and in Lebanon.

But it is hard to imagine that Mr. Netanyahu will be able to eliminate Hezbollah, just as he has been unable to eliminate Hamas. And it is harder still to imagine that Mr. Netanyahu will spend much time worrying about crossing Mr. Biden. He knows that if former President Donald J. Trump is elected, he will have a far freer hand to prosecute the war against Hamas and Hezbollah the way he sees fit.

“Israelis, especially the right wing of Netanyahu’s coalition, are determined to solve this, and they think they left this all to fester too long,” said Steven A. Cook of the Council on Foreign Relations, who just returned from a trip to talk with Israeli officials. “And they think they got bad advice from the U.S.”

Mr. Biden, for his part, he noted, “never really used his leverage over Netanyahu,” a reference to the president’s power to cut off specific kinds of military aid if the prime minister ignored his counsel. “And you don’t have leverage unless you are willing to use it.”

But the truth is that Mr. Biden will speak at a time of deep uncertainty about the future of America’s role in the world, including the war in Ukraine, escalating conflicts in the Middle East and growing economic competition with China.

Mr. Biden has vowed to continue pursuing a cease-fire that could end the fighting in Gaza, and his national security aides are feverishly working to forestall a broader war with Hezbollah in Lebanon. In Ukraine, Mr. Biden still faces urgent decisions, including whether to allow the use of American long-range weapons to strike deep into Russia.

And yet, there is a sense of precariousness when it comes to America’s longer-term intentions. Vice President Kamala Harris largely embraces Mr. Biden’s view of the importance of strategic alliances, though her specific policy views are still coming into focus as she campaigns on a compressed timeline. Former President Donald J. Trump promises a return to his “America First” brand of isolationism, while boasting about his own diplomatic skills.

The world leaders are gathering at the U.N. as multiple global crises are colliding with American politics in a way that could reshape how the United States confronts the world’s most difficult problems.

“For a world that is currently watching a war in Ukraine and a war in Gaza and the potential eruption of a war in Lebanon, where the United States is on this issue is both profoundly important and profoundly beyond their control,” said Jon B. Alterman, the director of the Middle East program at the Center for Strategic and International Studies in Washington.

Mr. Alterman said that for leaders of other nations, figuring out where America is headed after November’s elections “is one of the most important parts of their strategic calculus.”

To do that, many leaders are scrambling to meet with all three of America’s current or would-be leaders — Mr. Biden, Ms. Harris and Mr. Trump — during, or after, their visit to New York for the General Assembly this week.

The vice president had a closed-door meeting with Sheikh Mohammed bin Zayed, the president of the United Arab Emirates, at the White House on Monday afternoon, just hours after a similar meeting between the Emirati leader and Mr. Biden. Officials said Mr. Biden and Ms. Harris each was expected to raise the deepening violence in Israel and the Emirates’ involvement in the conflict in Sudan.

President Volodymyr Zelensky of Ukraine is set to meet with Mr. Biden in the Oval Office on Thursday, one day after he addresses the United Nations. Later on Thursday, Mr. Zelensky will meet separately at the White House with Ms. Harris — an indication that he is eager to bolster his own one-on-one relationship with her in case she wins the presidency in November.

After that meeting, aides say the White House has no plans for further engagement between Ms. Harris and foreign leaders or travel by the vice president outside the United States before Election Day, as she focuses all of her energies on the campaign trail.

There has been speculation about a possible Trump-Zelensky meeting as well, though a spokesman for the former president said on Monday that he had nothing to announce.

Mr. Trump has made no secret of his recent meetings with a steady stream of world leaders at his Mar-a-Lago estate in Palm Beach, Fla. On Sunday, he posted about a meeting with the emir and the prime minister of Qatar, who have been deeply involved in trying to negotiate peace between Israel and Hamas.

The emir “has proven to be a great and powerful leader of his country, advancing on all levels at record speed,” Mr. Trump wrote on social media after the meeting. “He is someone also who strongly wants peace in the Middle East, and all over the world. We had a great relationship during my years in the White House, and it will be even stronger this time around!”

During his time in office, Mr. Trump regularly questioned the need for decades-old alliances like NATO and abandoned newer ones, like the Paris climate accords and the Trans-Pacific Partnership.

Now, leaders in Europe, Asia and Africa are reading the tea leaves to see whether they can divine which future is likely to come to pass.

Will it be Ms. Harris’s interpretation of what Mr. Biden has called the “collective hope” of a world working together? Or will it be a return to bombastic threats from Mr. Trump, such as when he told the U.N. that he may “have no choice but to totally destroy North Korea”?

The stakes are high.

With Ukraine’s war against Russia entering its third year, Europe is actively confronting questions about its own security and whether it should wean itself from a longstanding reliance on American power as a guarantee against Russian aggression. Another Trump presidency is likely to force that debate to accelerate.

Mr. Biden is set to participate in a Security Council meeting on Ukraine on Tuesday that will include Mr. Zelensky. It will be a moment to underscore how successfully Mr. Biden has rallied much of the world to Ukraine’s side after Russia’s invasion in 2022.

In the Middle East, Mr. Biden’s steadfast support for Israel has left him more isolated among his global counterparts.

His diplomatic efforts have failed to bring an end to hostilities after the Hamas attacks in October that killed more than 1,200 people and left hundreds in captivity in Gaza. A recent escalation of violence between Israel and Hezbollah in Lebanon — including Israeli missiles attacks and exploding pagers that injured thousands of Hezbollah fighters — has prompted fears of a wider war.

John F. Kirby, the national security spokesman at the White House, said the president’s speech at the U.N. will outline “his vision for how the world should come together to solve these big problems and defend fundamental principles, such as the U.N. Charter.”

For the leaders in the audience, the question will be whether that vision is one that will continue after Jan. 20, Mr. Alterman said.

“The general attitude toward, ‘How does the world work and what role should the U.S. play in the world?’” he said, “strikes me as similar between Harris and Biden and fundamentally different between Biden and Trump.”

The push comes as Ukraine is slowly losing ground to mass Russian assaults in the eastern Donbas region and Russia continues to pound Ukraine’s civilian infrastructure, including electricity and heating plants, from a safe distance as winter is approaching.

Mr. Biden has been reluctant to give permission, careful as he has been since Russia invaded Ukraine in February 2022 not to escalate the war and risk a direct conflict between Moscow and the NATO alliance. President Vladimir V. Putin of Russia already blames NATO for the war and has made threats of retaliation, including frequent veiled references to his nuclear arsenal. But he has not retaliated militarily against the West even as NATO countries have gradually increased the quantity and quality of their arms supplies to Kyiv.

Finland’s new president, Alexander Stubb, joined the chorus for longer-range weapons in an interview with The New York Times, while Jens Stoltenberg, in his last days as NATO secretary general, has all but done the same, while noting diplomatically that each country must decide for itself.

Mr. Stubb, who will speak for all the Nordic countries at the U.N. General Assembly, was blunt.

“I call upon our allies in the global West, including the United States, to allow Ukraine to fight without one hand tied behind its back and to lift those restrictions,” he said in a wide-ranging interview on Thursday from Helsinki. “We need to continue to support Ukraine, starting with finance, starting with ammunition, starting with vehicles, and also with allowing Ukraine to use weapons as itself pleases, as long as it’s in self-defense and within the framework of international rules.”

Mr. Stoltenberg has been unusually outspoken as he prepares to leave office at the end of the month. “I fully understand the desire from Ukraine to have as few restrictions as possible,” he said in an interview with Christiane Amanpour of CNN. “There are less restrictions now than just some months ago,” he said, “and that’s the right thing to do,” because “this is a war of aggression” and “according to international law, self-defense is legal.”

Ukraine, he said, “has the right for self-defense and that includes striking legitimate military targets on the territory of the aggressor, Russia.” And NATO countries, he went on, “have the right to provide the weapons that they are using to do so without us becoming a party to the conflict.”

Both Mr. Stubb and Mr. Stoltenberg noted that various allied “red lines” had already been crossed, with the provision to Ukraine of Leopard II battle tanks, Storm Shadow and Scalp cruise missiles, longer-range artillery and even American-made F-16 fighter jets. All were subject to fierce debates over whether they would prompt Mr. Putin to escalate the fight and even use nuclear weapons.

The new prime minister of Britain, Keir Starmer, has also pushed Mr. Biden to allow the use of these longer-range weapons, like Storm Shadow and Scalp, its French version, to hit bases farther into Russia from where Mr. Putin launches attacks.

Adm. Rob Bauer, chairman of the NATO Military Committee, said last week that attacks deep inside Russia were legal, because “to weaken the enemy that attacks you, you not only fight the arrows that come your way but also attack the archer.” Still, he said, nations providing weapons can demand “certain limitations” in their use, “because they feel responsible for those weapons.”

Mr. Stubb, whose country joined NATO only in response to the war and shares a long border with Russia, has few illusions about what he considers NATO’s need to stand up to Russian aggression in Ukraine. “Russia is an imperial power that has expansion in its DNA,” he said.

“So what we need to do is to convince Putin that there’s no point for him to continue this war, and I think Putin needs to lose both the war and the peace, because the only thing that he understands is power,” Mr. Stubb said.

“The key is to allow Ukraine to fight this war without any kind of restrictions, and everything after that is secondary,” Mr. Stubb said. “The more we allow Ukraine to act, the sooner we will achieve peace negotiations.” Then the West must provide Kyiv with security guarantees leading to membership in both NATO and the European Union, he said.

Mr. Stoltenberg agreed. “By giving Ukraine more weapons, we can make Putin realize he cannot get what he wants by force and make it so costly that he will have to accept Ukraine has a sovereign, democratic right to persist as a sovereign, democratic country,” he said in a speech last week in Brussels to the German Marshall Fund. “The paradox is that the more weapons for Ukraine we are able to deliver, the more likely it is that we can reach a peace and end to the war. And the more credible our long-term military support, the sooner the war will end.”

Given raging global conflicts, including in the Middle East and Africa, the United Nations must re-engage in true peacekeeping, Mr. Stubb said. To that end, in New York, he said he would propose an expansion of the U.N. Security Council to include five new permanent members, one from Latin America, two from Asia and two from Africa, coupled with 10 rotating members and an elimination of the single-country veto, “which makes the Security Council dysfunctional,” he said. He would also propose that a member country “in blatant violation of the U.N. Charter and international law, such as Russia is right now in Ukraine,” should be suspended by a vote of the General Assembly.

Serious changes to the Security Council have proved impossible in the past, given the veto, he concedes, but he insists that the crisis demands new thinking. The veto might be replaced by weighted voting, he said, but it was crucial to include members of the so-called Global South, developing countries largely left out of post-1945 international institutions.

Those countries may see hypocrisy in the criticism of Russia and the support for Israel in Gaza, he said. “But my argument to our friends in the Global South, who are sometimes justifiably expressing doubts about Western double standards, is to say that this war in Ukraine sets the scene for how other nation-states can behave in the rest of the world,” he said. “If we now allow Russian imperialism to take place, we will see this happening elsewhere in the world, and that’s why I think this is a key struggle for all of us.”

In that agreement, the 2015 Paris accord, they promised to act and acknowledged a bare truth: Climate change threatens all of us, and we owe it to each other to slow it down. Countries agreed to nudge each other to raise their climate ambitions every few years, and the industrialized nations of the world — which had prospered from the burning of coal, oil and gas — said they would help the rest of the world prosper without burning down the planet.

Turns out, geopolitics can be as unpredictable as the weather.

Three big things have shifted since the climate accord that, together, have sunk the prospects of global climate cooperation to a low point. China has raced ahead of every other country, including the United States, to dominate the global clean-energy supply chain, fueling serious economic and political strains that undermine incentives to cooperate. Rich countries have failed to keep their financial promises to help poor countries shift away from fossil fuels. A widening gyre of war — from Ukraine to Gaza and now, in Lebanon — has become an impediment to global climate consensus.

“Major emitting countries are much less likely to work cooperatively on climate due to geopolitical tensions and concerns about supply-chain security than they were in 2015,” said Kelly Sims Gallagher, a former White House adviser who is now dean of The Fletcher School at Tufts University.

Then there’s the biggest, most consequential uncertainty of all: the coming U.S. elections.

China’s Transformation

China is the world’s largest producer of solar panels. Also wind turbines. Also batteries for electric vehicles. It manufactures more electric cars, buses and motorcycles than any other country.

It also processes the vast majority of the world’s cobalt and lithium, essential components in the batteries that will help electrify everything from trucks to factories to advanced weaponry.

In short, it holds the keys to the treasure chest of the renewable-energy transition, even as, paradoxically, it burns more coal than any other country. That makes China the biggest emitter of greenhouse gases at the moment, while the United States is the biggest emitter in history.

China’s dominance of clean-energy goods has sparked a protectionist backlash few would have expected when the Paris accord was signed in 2015 — with the U.S. and China as two of its most important backers. Today, however, Western countries, fearing that they will fall even farther behind, have imposed nearly insurmountable tariffs on China’s electric vehicles. And they have sought to eliminate Chinese-processed metals from their own factories.

That has added a new stumbling block to climate diplomacy between the world’s biggest emitters. It’s not helped by rising tensions between Washington and Beijing. The two sides are still talking, but they’re not agreeing on much. The global energy transition is getting bogged down as they quarrel.

“There’s no question that geopolitics are more challenging than they were when the Paris Agreement was struck,” said Ani Dasgupta, president of the World Resources Institute.

But he took pains to note that many countries continue to push the world’s powerful to come together, and with some success. “The biggest change, and a welcome one, we have seen since Paris is the rise of climate leadership from the Global South,” he said, referring to low-income nations that often feel disproportionate effects from global warming.

The Money Problem

Money has bedeviled climate diplomacy for decades. There has been intense disagreement over who should pay, and how much.

A handful of countries — the United States, most of Europe, Canada, Australia and Japan — are responsible for most of the greenhouse gas emissions that have caused the planet to heat up over the past century. But each of those countries, in their own way, argues that they alone can’t foot the bill for a global fix.

They also argue that China in particular, now the world’s second biggest economy and its biggest polluter, should also pony up money to aid low-income countries.

The one explicit acknowledgment of this obligation has been the creation of a formal Loss and Damage Fund to help poor countries cope with climate disasters made worse by the greenhouse gases emitted by wealthy nations. A little over $700 million has been pledged, a drop in the bucket of what it costs even one country to recover from one climate disaster. (The European Commission allocated $10 billion this week to help Central European countries respond to the latest floods.)

Recently, a few courts have begun to take up cases that strive to penalize the industry or require fossil fuel companies to help pay the cost of fighting climate change. But even if the plaintiffs were to prevail, any decisions would likely be years in the future.

Meanwhile, the costs of climate change have piled up for low-income countries, many of which are also heavily indebted. On average, African nations are losing 5 percent of their economies because of floods, droughts and heat, according to the World Meteorological Organization. Many are spending up to a 10th of their budgets managing extreme weather disasters.

“For developing nations, especially those on the front lines of climate disasters, this is not just an injustice, it’s a betrayal of trust and humanity,” said Harjeet Singh, global engagement director at an activist group called the Fossil Fuel Non-Proliferation Treaty Initiative.

With War, Shifting Alliances

The Russian invasion of Ukraine has lifted energy security to the top of the agenda for big world powers. That has both strengthened the argument to shift to renewable energy — but also shifted the focus of many world leaders from emphasizing a transition away from oil and gas to making sure they have enough of it for their energy needs.

It has also buoyed the fortunes of oil and gas producers worldwide. At the same time, food and fuel costs have risen worldwide, and with it, hunger.

If the war in Ukraine scrambled the economics of the energy transition, then the war in Gaza scrambled its politics, driving up distrust and realigning geopolitical allegiances. Western hegemony over global trade, including of fossil fuels, has faded.

Both China and India, as well as Turkey and Iran, two sets of rivals, have made deft energy deals with President Vladimir V. Putin of Russia, allowing Russian oil and gas to enjoy new markets as Europe weans itself from Russian energy. The United States has, in turn, sought to counter that new dynamic by exporting more of its own oil and gas than ever.

This week at the United Nations, there are likely to be some pointed reminders to world leaders, particularly from the 20 largest economies, known as the G20, to rally around climate action.

The United Nations’ top climate official, Simon Stiell, whose grandmother’s home on the Caribbean island of Grenada was destroyed by Hurricane Beryl earlier this year, said as much in a recent speech. “It would be entirely incorrect for any world leader, especially in the G20, to think, ‘Although this is all incredibly sad, ultimately it’s not my problem,’” he said.

The wildest wild card in all of this is what happens in November, when Americans go to the polls.

In his first term as president, Donald Trump pulled the United States out of the global climate accord. Should he return to the White House, he has promised to do so again.

As Tim Benton, a fellow at Chatham House, a London-based research organization, wrote recently, “a new Trump administration promises only — directly and indirectly — to frustrate ambitious, effective climate policies in the U.S. and abroad.”