“It’s a possibility, however small,” said Tianle Yuan, a senior research scientist at the University of Maryland, Baltimore County. He explained that the record warmth could instead merely reflect a temporary fluctuation on top of the long-term warming trend spurred by human-caused climate change.

Some climate researchers suspect that a drastic reduction in air pollution from ships has allowed more sunlight to radiate into oceans, a conclusion others vigorously criticize. Meteorologists also say a weakening of Atlantic winds may be encouraging warming; normally these winds help cool waters and carry sun-blocking plumes of Saharan dust.

Scientists nonetheless agree on this: Conditions are ever ripening for extreme heat waves, droughts, floods and storms, all of which have proven links to ocean warming.

That means more record-breaking conditions and events are to be expected, said Michael Mann, a climatologist at the University of Pennsylvania. That inevitability “underscores reasons for concern and the urgency of climate action,” he said.

The trend has developed over just the past few months, with its duration and intensity elevating scientists’ concern in recent days.

By that time, temperatures averaged across Earth’s oceans, excluding polar regions, had surged two-tenths of a degree Celsius above observations at the same point last year — and nearly a full degree above the average from 1982 to 2011.

In the Pacific Ocean, warming temperatures are to be expected during El Niño — its impacts on weather around the world stem from warmer-than-normal surface waters along the equatorial Pacific. But the extreme warmth extends beyond the Pacific. Record warmth is also occurring in the equatorial and northern Atlantic — and in the tropics, where hurricanes form.

“This is totally bonkers and people who look at this stuff routinely can’t believe their eyes,” Brian McNoldy, a hurricane researcher at the University of Miami, wrote on Twitter. “Something very weird is happening.”

One theory drawing attention — and disagreement — ties back to a regulation imposed on the maritime shipping industry in 2020. The International Maritime Organization required ships to use fuel with drastically reduced sulfur content, in an effort to reduce sulfate air pollution that harms human health.

Those pollutants tend to reflect sunlight back into space, preventing it from reaching Earth’s surface — heavy air pollution is the reason India, for example, is among the slowest-warming places on the planet.

“We tweak things here and there, and it gets messier somewhere else,” DiNezio said.

Other scientists argue there’s no data to show that the pollution reductions are to blame for such dramatic ocean warming, however.

The only peer-reviewed research exploring it, a paper published in 2009, found a minimal link between the pollution and ocean temperatures, Mann said — with an effect on the order of 0.05 degrees Celsius, a small fraction of the warming observed lately.

Weather patterns and the influence of El Niño are also proving conducive to ocean warming — something many climate scientists are stressing as evidence that the trends, while cause for some concern, are not reason for panic.

Those winds were unusually weak this spring, potentially part of a feedback loop that is discouraging the trade winds from developing.

“When you start to warm the eastern Atlantic, that tends to load the dice for weaker winds feeding back into the tropical Atlantic,” said Phil Klotzbach, a Colorado State University research scientist focused on hurricanes.

Those conditions are occurring against the backdrop of El Niño, known for planetary warming, as well as the influence of steadily increasing greenhouse gases in the atmosphere. So it makes sense that temporary changes in wind and weather patterns could have a bigger influence on ocean temperatures than the same conditions might have in the past, scientists said.

“You have natural variability, and you have climate change on top of it,” Klotzbach said.

Mann criticized those sharing alarmist and sometimes out-of-context charts and suggesting they are proof of some imminent cataclysm.

“This is no better than when climate change deniers exploited natural climate variability a decade ago,” he said in an email, referring to data that suggested a slowdown in global warming from about 1998 to 2012.

Instead, he said, “the truth is bad enough”: Steady warming from decades of greenhouse gas emissions has made conditions like those occurring now in Earth’s oceans all the more probable.

And regardless of the cause, the effects could be dramatic, Yuan said.

“No matter what the cause is, it’s going to affect weather in both North America and Europe,” he said. “We know that.”

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