With the planet in the grips of its highest temperatures in more than 100,000 years, scientists with the United Nations weather agency have crunched the numbers and come to a stark conclusion: More record-hot years are all but inevitable.

In the next five years, there’s a nearly 90 percent chance Earth will set yet another record for its warmest year, surpassing the scorching highs experienced in 2023, the World Meteorological Organization said in a report Wednesday.

The chances are almost as great that, in at least one of these five calendar years, the average global temperature will be 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, higher than it was at the dawn of the industrial age. That’s the level of warming that countries set out to avoid under the 2015 Paris Agreement.

“The target of limiting long-term global warming to 1.5 degrees Celsius is hanging by a thread,” the United Nations secretary general, António Guterres, said in a speech in New York City on Wednesday. He called for urgent action in a number of areas, including slashing carbon dioxide emissions and adopting renewable energy, helping poor countries finance their climate plans, and clamping down on the fossil fuel industry.

On the last subject, Mr. Guterres reiterated past exhortations to end taxpayer subsidies for oil and gas. But he also turned his attention to a new target: He urged governments to ban advertising by fossil-fuel companies, comparing oil and coal producers to the tobacco industry, which faces advertising restrictions worldwide. And he urged the news media and tech companies to stop displaying their ads.

“Fossil fuels are not only poisoning our planet; they’re toxic for your brand,” Mr. Guterres said, referring to advertising and public-relations agencies. “I call on these companies to stop acting as enablers to planetary destruction.”

Several publications, including the The Guardian newspaper, have stopped accepting fossil fuel advertising. The New York Times accepts ads from oil and gas companies with some restrictions, including prohibiting sponsorship of its climate newsletter and climate events, a company spokesman said. The Times also doesn’t allow fossil fuel companies to buy all of the ad spots on individual episodes of its podcast “The Daily.”

Earth’s latest streak of record-shattering warmth began in the middle of last year and has not let up as another summer approaches in the Northern Hemisphere.

Last month was the planet’s warmest May on the books, the European Union’s Copernicus Climate Change Service announced on Wednesday. That made it the 12th-straight month in which the average temperature worldwide exceeded all past records for the time of year. Across that 12-month stretch, the mercury was 1.63 degrees Celsius warmer on average than it was during preindustrial times, according to Copernicus.

The Paris Agreement says the 1.5-degree target is a “long-term” goal. Technically speaking, this means the world will have failed to uphold the pact only if temperatures exceed the threshold for many years, even decades, not just a single year.

“Temporary breaches do not mean that the 1.5 goal is permanently lost,” Ko Barrett, the deputy secretary-general of the World Meteorological Organization, said at a news conference. Still, what now seems clear, she added, is that such breaches are going to be more and more common.

The effects of the abnormal warmth have been felt across the globe. In India and other parts of South Asia, temperatures have climbed well past 110 degrees Fahrenheit in recent weeks, pushing many people to the brink. Millions of Americans in California, Nevada and Arizona are experiencing their first intense heat wave of the season this week.

Recent flooding in Brazil caused widespread death and destruction, and could become the country’s costliest disaster on record. The torrential, multiday rains that caused the deluges were made twice as likely by extra heat energy added to the atmosphere by human activity, scientists said this week.

Throughout the world’s oceans, coral reefs are suffering the most widespread bleaching ever observed, in large part because of how hot the water has been. The National Oceanic and Atmospheric Administration expects this year’s Atlantic hurricane season to be exceptionally stormy, with 17 to 25 named tropical cyclones. Record ocean temperatures, which provide the thermodynamic fuel for storms to form and intensify, are a major factor.

As global warming continues, “this string of hottest months will be remembered as comparatively cold,” said Carlo Buontempo, Copernicus’ director. By quickly cutting emissions of greenhouse gases, Earth might be able to cool back down to today’s temperatures by century’s end, he said.

There’s at least one reason to believe some temporary relief is on its way. El Niño, the natural climate phenomenon, is fading. During periodic El Niño events, tremendous amounts of heat are redistributed in the Pacific Ocean, leading to shifts in global weather patterns that typically cause the planet as a whole to be warmer. This contributed at least in part to 2023’s record temperatures.

Other contributors might stick around for longer. In a study published last week, a team of scientists led by Tianle Yuan, a geophysicist at the University of Maryland, Baltimore County, estimated that the planet could be experiencing additional warming right now for a counterintuitive reason: recent regulations that slashed air pollution from ships.

The burning of fuel oil releases planet-warming carbon dioxide, but it also releases sulfur compounds that can have a modest opposing effect. Once they’re in the atmosphere, these compounds transform into particles that help cool the globe, either by reflecting sunlight back to space or encouraging more clouds to form.

These pollutants still harm human health and ecosystems, which is why the International Maritime Organization set new limits on sulfur emissions from ships starting in 2020. But, in doing so, the agency might inadvertently have helped make Earth somewhat warmer today than it would otherwise have been, Dr. Yuan and his colleagues estimated.

To scientists, the foremost driver of warming remains clear: Atmospheric levels of carbon dioxide, methane and nitrous oxide, the three most important human-caused heat-trapping gases, have continued their steady upward climb. At current rates of emissions, it might only be five or so more years before humans have altered the atmosphere’s chemistry so significantly that it becomes all but impossible to stop warming from surpassing 1.5 degrees Celsius, scientists have estimated.