As world leaders gather at the United Nations this week, they face no shortage of divisive issues: An ongoing global pandemic, economic strife on numerous continents, and conflict and human rights concerns from Afghanistan to Haiti.

But with only six weeks left until a crucial global climate summit in Scotland, presidents and prime ministers also face pressure to set aside these diplomatic tensions and act quickly and collectively to slow the warming of the planet — something they have struggled to do in the past.

“We have reached a tipping point on the need for climate action,” U.N. Secretary-General António Guterres warned Thursday, in one of his latest pleas for unity and urgency. “The disruption to our climate and our planet is already worse than we thought, and it is moving faster than predicted. … We must act now to prevent further irreversible damage.”

This week’s U.N. General Assembly marks one of the last high-profile opportunities for countries to publicly commit to more ambitious, concrete action to cut greenhouse gas emissions ahead of November’s climate summit in Glasgow. So far, such promises from some of the world’s biggest economies have failed to materialize, despite a full-court press from the Biden administration, the European Union and other advocates.

A U.N. report published Friday warned that while scores of countries have outlined new climate plans this year, if other nations — including China and India — fail to pursue bolder plans, greenhouse gas emissions could actually increase by 16 percent by the end of the decade. That could place the planet on a path to warm by 2.7 degrees Celsius (4.9 Fahrenheit) by the end of the century.

People who never considered themselves at risk from climate change are waking up to floods and fires. (Monica Rodman/The Washington Post)

The world already has warmed more than 1 degree Celsius compared to preindustrial times, and scientists say that each fraction of additional warming will bring worsening catastrophes, from more frequent flooding to more intense wildfires and heat waves.

On Monday, Guterres and U.K. Prime Minister Boris Johnson are scheduled to host a closed-door gathering — part in person, part virtual — of several dozen national leaders, including a mix of the world’s largest and most powerful nations alongside poorer countries hit hardest by climate change.

Psychological research shows that climate change can alter an individual's mental health both directly and indirectly, impacting how we respond to this crisis. (John Farrell/The Washington Post)

It is the latest effort to nudge large emitters to embrace more aggressive climate action. Such promises are essential if the world is to have any chance of meeting the most ambitious aim of the Paris climate accord: Limiting the increase in global warming to 1.5 degrees Celsius (3.6 Fahrenheit) compared to preindustrial levels.

The gathering is also aimed at getting richer, developed countries to make good on long-unfulfilled promises to provide billions of dollars in financing to help cash-strapped, vulnerable nations adapt to the effects of climate change and build greener economies. The failure to do that has led to animosity and distrust.

“They have to send some messages that we can still hang together,” Laurence Tubiana, chief executive of the European Climate Foundation, said of the need for countries to separate trade wars, national security squabbles and other fights from the need to join forces on climate change.

“It’s a common threat,” said Tubiana, a key architect of the 2015 Paris agreement. “Climate change ignores power politics. It doesn’t care how many armies you have, how many weapons you have. … We saw in the pandemic when we don’t organize collectively how damaging it is. Climate is just much worse.”

The landmark 2015 Paris agreement, supported by nearly every nation in the world, was designed with the expectation that countries would ramp up their voluntary commitments to cut greenhouse gas emissions over time. The planned summit in Glasgow, delayed a year by the pandemic, has long been where nations are expected to show up with bolder, tangible commitments five years on from Paris.

There are signs that shift is happening, albeit in fits and starts.

Scores of countries have already announced more aggressive targets, even if they aren’t yet as aggressive as scientists say is necessary. That includes the United States, which under President Biden has committed to cut emissions at least in half by the end of the decade.

The administration has joined forces this year with the European Union and the United Kingdom, home to even more stringent climate targets, to try to compel the world’s largest emitter, China, and other major economies to embrace near-term ambitious goals to put the world on a better trajectory.

On Friday, the United States and the European Union also agreed to a “global methane pledge” that would slash emissions of the potent greenhouse gas by nearly a third by 2030 compared to 2020 levels. The United Kingdom and signed onto the initiative, as did Argentina, Mexico, Indonesia and several other nations. The hope is that still more countries will follow.

Yet serious questions remain.

“The window is rapidly closing for major emitters like China to make new commitments that will really matter in bending down global emissions,” Paul Bledsoe, a former Clinton White House climate adviser, now with the Progressive Policy Institute, said in an email. “Despite new pledges by the U.S. and E.U., unless other nations begin to step up well ahead of Glasgow, the entire international community risks being blamed for inadequate action.”

Since the Paris agreement, the world has changed in profound ways, both in climate diplomacy and in climate science, where it has become only more clear that humans’ greenhouse gas emissions are feeding intense fires, floods, heat waves and other extreme weather events that are claiming lives and costing fortunes.

In 2014, President Barack Obama and Chinese leader Xi Jinping sealed a deal to limit greenhouse gas emissions a full year ahead of the gathering in Paris, making that global accord possible.

The run-up to the U.N. summit in Glasgow has proven vastly different.

A year ago, there were no advance negotiations, in part because President Donald Trump, who called climate change a hoax and played it down as a threat, made the United States the only nation to formally withdraw from the Paris accord. Also, much of the world was shut down because of the novel coronavirus.

“The ability to come together has really been upended by covid,” said Pete Ogden, president of the U.N. Foundation and former senior director for energy at the Domestic Policy Council and National Security Council.

The Biden administration, meanwhile, has been trying to make up for lost time.

On his first day in office, Biden rejoined the international climate treaty. He dispatched former secretary of state John F. Kerry to crisscross the globe in an effort to forge the most ambitious climate deal possible. He pushed fellow leaders to match their rhetoric with action at a spring White House summit and at the Group of Seven meeting in June. And he is working to get Congress to approve a $3.5 trillion spending package that would include far-reaching climate actions, which is critical for the United States to make progress toward its 2030 emissions target.

On Friday, Biden again convened a virtual meeting of major economies to make a pitch for bolder promises. “The time to act is really narrowing,” he told the group.

Now, with the success of this fall’s climate summit hanging in the balance, experts see the U.N. assembly this week as one of the last likely venues for needle-moving commitments.

“I think it’s important that there be major announcements about taking steps forward,” said David Sandalow, a veteran of the Clinton and Obama administrations and now a fellow at Columbia University’s Center on Global Energy Policy. “That needs to include action on the part of the major emitters but also from major institutions, financial groups and others.”

This week’s U.N. gathering also provides a rare chance ahead of Glasgow for leaders of rich nations and smaller, poorer nations to address a relationship harmed by broken promises, said Jennifer Morgan, executive director of Greenpeace International. One central promise was that developed nations would provide $100 billion annually to help developing countries build greener economies and deal with climate-fueled catastrophes. It has never been fully funded.

“Right now, I don’t think there’s a lot of trust in developing countries that climate change is a collective thing we’re going to solve together, because it isn’t happening on covid,” Morgan said. “Developed countries do need to come forward and build that trust, and we are not there yet.”

But that will only come by giving credence to the concerns of those on the front lines of climate change.

“The smaller and vulnerable countries, the small islands, Africa — for them it is life and death every day now,” she said. “They are the voice in the room that brings that humanity about what’s at stake and how important it is to have this collaboration. It’s not some faraway issue.”

As he has before, Guterres on Thursday implored leaders to act with resolve and set aside other political differences.

He noted that the world remains “far from meeting the goals” of the Paris agreement, that the past five years are among the hottest on record and that fossil-fuel emissions are rebounding to pre-pandemic levels. Greenhouse gas concentrations are hitting highs, and extreme weather events have become more common and costlier.

“These changes are just the beginning of worse to come,” Guterres warned, again pleading with nations for real commitments, not just speeches.

“Nothing less will do,” he added. “We really are out of time.”