Are record warm oceans reason to fret? Scientists are divided.

A steady and remarkable rise in average global ocean temperatures this year is now outpacing anything seen in four decades of satellite observations, causing many scientists to blare alarm over the risks and realities of climate change. But even those typically aligned on climate science can’t agree on what, exactly, triggered such rapid warming and how alarmed they should be.

They say there is so far no evidence the planet has passed some climatic tipping point - though it is also too soon to rule that out.

“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.

Regardless of what is behind the spike in ocean temperatures, scientists are on edge about it. On Twitter, viral posts sounding alarm bells have triggered heated debates about the potential causes and whether the rise is reason to panic.

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.

Whether air pollution and windblown sand have anything to do with the oceans’ rapid warming, it is occurring after years of gradual and accelerating heating, and just at the onset of the El Niño pattern, which is known to supercharge global warming and extreme weather.

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.

Unprecedented warmth developed quickly

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

The first signs of unusual ocean warming appeared in March, raising eyebrows among climate scientists. At the time, forecasts suggested El Niño might soon develop, bringing its own warming influence, but it wasn’t until last week that the National Oceanic and Atmospheric Administration declared that the ocean-atmosphere pattern had actually come to fruition.

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.

Average global ocean temperatures hit a record high in May, a second consecutive month of unprecedented ocean warmth, according to data NOAA released Wednesday.

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, including 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.”

Could cleaner air be encouraging warming?

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.

A team of researchers at the NASA Goddard Space Flight Center, including Yuan, found last year that the change did significantly reduce the concentration of those pollutants over parts of the northern Atlantic and Pacific, between busy trade routes from Asia to North America and North America to Europe.

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.

Yuan and other scientists say it’s possible that the disappearance of that cooling effect is behind at least some of the rapid warming, and that a stubborn La Niña - the cooling climate pattern that dominated the past three years - masked the change until now.

“I don’t know how big the effect is. I hope it’s small. I hope all this data is deceiving me,” said Leon Simons, a climate researcher in the Netherlands. “I don’t think so.”

It could be an example of the unintended consequences of human influence on a complex climate system, said Pedro DiNezio, an associate professor at the University of Colorado.

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

Other scientists argue there is no data to blame the pollution reductions 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.

The possible role of weather patterns in boosting temperatures

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

Shifts in atmospheric circulation have translated to the disappearance of an area of high pressure that often sits over the eastern North Atlantic, sending strong trade winds from western Africa toward North America. The winds encourage warm surface waters to evaporate and cool, and also typically carry sand from the Sahara Desert over the Atlantic. Much like the sulfate air pollution, the sand serves to block sunlight and reflect it back into space, preventing some warming of the waters below.

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.

The weak winds may also be affecting what is known as the North Atlantic gyre, a circulation of currents that usually sends cooler waters west of the Azores down into the tropics.

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 graphs 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 around 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.”