UNITED NATIONS — Carnage in Syria, the chasm between Israelis and Palestinians, climate change and terrorism rank among the heavy issues that 193 United Nations member states will ponder during the 71st UN General Assembly, which revs up Tuesday with speeches by heads of the world’s nations.

The gathering in Manhattan, which experts and diplomats view as an annual renewal of focus on the world’s problems, will be the last that President Barack Obama and UN Secretary-General Ban Ki-moon will attend during their eight- and 10-year tenures in office, respectively.

Last week, Ban opened the General Assembly at a prayer service where he stated wistfully that both the service and session have “deeper meaning” as he counts down his days as leader of the world body. He steps down Dec. 31.

“The opening of the General Assembly is itself a profound act of faith,” he said. “Faith in humanity, faith in our shared future, faith in our conviction that together, we are stronger.”

Leaders meet amid signs of hope and despair around the globe.

  • North Korea boasts ever more sophisticated weapons testing, launching a ballistic missile this month that skimmed Japan’s shores and conducting a nuclear test a few days later.
  • A fragile cessation of hostilities last week took hold in Syria, the site of a civil war that has claimed more than 300,000 lives, spawned a humanitarian crisis and fueled the exodus of millions of refugees into Jordan, Turkey, Lebanon and Europe.
  • Islamic State, al-Qaida, Boko Haram and others continue to foster and practice terrorism on several continents.
  • The world continues to get warmer as nations are slow to ratify the Paris agreement designed to slow climate change.
  • Yemen, Burundi, Libya, Nigeria, Somalia, South Sudan and others grapple with internecine and external strife.

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“This challenging environment also provides a window of opportunity as Obama and Ban Ki-moon prepare to leave office,” said Katie Laatikainen, a professor of political science at Adelphi University in Garden City, who said the agreement on climate change is perhaps the best bet for international cooperation.

“There is great incentive to move this forward, and while there is a great deal of gloom and doom elsewhere in the multilateral landscape, this would be a momentous achievement completed in record time,” she said. “For both Obama and Ban Ki-moon, entry into force of the Paris agreement would be a successful bookend to the beginning of their tenures in office.”

Indeed, Ban said last week during a news conference that he is most proud of his role in the landmark agreement signed by 200 nations in December. He also was pleased to have presided over the implementation last year of the Sustainable Development Goals, a set of 17 aims designed to “end poverty, protect the planet and ensure prosperity for all.”

Those principles form the theme of the General Debate.

Phyllis Bennis, a UN expert who is director of the New Internationalism Project at the Institute for Policy Studies in Washington, said the General Assembly, where each nation has a single vote, “has historically been a very important venue for major shifts in global policy.”

But debates over solving problems like that of Syria’s refugee crisis must center on solutions, she said.

“The problem is that you have a group of global officials trying to put a Band-Aid on a massive bleeding wound that needs not only a tourniquet but something to stop what’s pumping the blood,” she said, referring to the war itself as the cause of the refugee and humanitarian crisis in Syria.

The yearly gathering also affords a unique opportunity for presidents, prime ministers and other leaders to make headway, because face-to-face meetings occur — if only because top decision-makers and their advisers are in the same building talking in real time, not in far-flung capitals communicating through envoys at the UN.

Obama is expected to spend as many as four days in New York, potentially rubbing elbows with his counterparts in the nations that can best tackle the world’s problems.

Monday’s special high-level session on refugees and migrants, for example, will precede the General Debate by a day, as last year the climate change talks did, with the agreement in Paris coming a few months later.

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Presidents and prime ministers could sit in for their ambassadors at the UN Security Council or the General Assembly chambers — as they did in tackling the Ebola crisis two years ago — to take on Syria’s obstacles, discuss antimicrobial resistance or spark renewed talks between Palestinians and Israelis.

“We’re at a critical moment and need immediate action on climate change,” said Peter DeBartolo, director of the Levermore Global Scholars program at Adelphi. “While the United Nations was initially founded to ‘save succeeding generations from the scourge of war’ and this still continues to be one of its primary purposes, last December’s agreement in Paris shows us that the global community now also understands that it must unite today to save succeeding generations from the scourge of possible ecological collapse, as well.”