As seas get hotter, South Florida gets slammed by an ocean heat wave

An ocean heat wave in waters around Florida has scientists worried about cascading disasters, from fueling hurricanes and coral bleaching to exacerbating record heat on land.

Ocean temperatures have soared five degrees above normal since early July. This warming has been ignited by an El Nino weather pattern that's collided with human-caused climate change.

"It's bonkers. I don't know how else to put it," said Ben Kirtman, an atmospheric scientist with the University of Miami Rosenstiel School. "Normally when you break records, you break records by a tenth of a degree, maybe a quarter of a degree. ... Here, we're breaking it by five degrees."

If scientists were to model the chances for such a spike in temperature, he said, it would amount to one in 250,000 years.

"It's out of bounds from what we've seen," Kirtman said.

Summertime seas around South Florida typically average about 88 degrees. But beginning in July, ocean monitors stationed along the coast began recording temperatures hovering in the low 90s. In Florida Bay, the wide shallow bay between the Florida Keys and the Gulf of Mexico, temperatures climbed above 98 degrees.

More ocean heat waves coming

South Florida's ocean heat wave arrived as global ocean temperatures have steadily climbed since April. That prompted forecasters at the National Oceanic and Atmospheric Administration to predict that half the planet's oceans could undergo heat waves by September.

In its last assessment of the warming planet, the United Nations Intergovernmental Panel on Climate Change found the Earth has heated up 2 degrees Fahrenheit in the past two centuries. Scientists warned that marine heat waves, like the one inflaming waters around Florida, would become more commonplace. That increasing heat, the IPCC said, could likely push some sea life "to the limits of their resilience."

South Florida is already seeing some impacts. Warmer ocean waters reduce oxygen levels and that could impact fish populations. Three years ago a rare fish kill spread across waters off Miami as rising temperatures sucked oxygen from Biscayne Bay. Warming waters could also endanger spawning grounds for Atlantic bluefin tuna in the northern Gulf of Mexico, one of only two places where these tuna spawn. Hotter seas around Florida could also warm trade winds that help cool the state. That could exacerbate record heat already occurring on land.

This summer's warming coincided with an emerging El Nino, a weather pattern that increases water temperatures in the Pacific and warms up the planet. But Kirtman said El Nino likely amplified temperatures already starting to creep upward.

"Certainly part of that warming is coming from El Nino, which is emerging. But usually there are cool spots associated with El Nino. We're not seeing any cool spots," he said.

That raises the question of what exactly is happening this year, Kirtman said.

"Is this just a ratcheting up of climate change, and then things are going to plateau for a little while and then there'll be another ratchet up?" he said. "We don't know."

Scientists brace for coral bleaching

Corals are among the most precarious sea life struggling with climate change. Reefs around Florida and the Caribbean have struggled mightily over recent decades as increased pollution and disease have left them crippled. That has weakened their ability to function as a powerful barrier to hurricane storm surges.

In 2014, an outbreak of stony coral disease that started off Miami spread up and down Florida's reef and into the Caribbean. Florida's reef is the only barrier reef in the waters of the continental U.S. The disease knocked out foundation-building boulder coral on reefs that had already lost about 80% of their corals since the 1970s. The loss of those mounding coral that help bulk up reefs prompted scientists from across the country to form an emergency response to try to stop the spread and diagnose a cure.

The ocean heat wave now has scientists bracing for widespread coral bleaching.

"It's not as if it's just warming up here in Florida," said Andrew Baker, a coral researcher at the University of Miami's Rosenstiel School. He's been looking for ways to make coral more resilient to hazards from climate change. "This is clearly kind of a Caribbean region-wide thing. And that's why people are starting to think that it probably has some legs and is likely to be with us for a while."

Warm summer waters typically trigger outbreaks of bleaching, when coral expel the algae they need to survive. But Baker said that warming typically occurs later in the season.

"That's really why people are scared, because we have potentially another six or eight weeks of continued seasonal warming that's going to add on top of this heat wave," he said. "That's really where the danger lies."

Baker is now working with the U.S. Department of Defense to develop more heat tolerant coral as part of a reef resilience project that could total more than $28 million. The project set a 2027 deadline to breed coral able to withstand a five-degree Fahrenheit rise in ocean temperatures.

"But now this summer we have temperatures that are already five or six degrees Fahrenheit warmer than the normal temperatures should be right now. So nature is outpacing even some of our most ambitious goals," he said.

In the next few weeks, Baker said scientists will decide whether they want to move some coral into labs in advance of summer spawning, when corals release millions of eggs and sperm to produce babies. Heat stress can hamper that spawning. By moving them to labs, researchers can collect the babies and then release them back into the ocean. Researchers in his lab plan to inspect coral near Miami this week. In August they will look at a site in the Keys where more heat tolerant coral have already been planted.

"Even if we were to do that with just a couple of dozen corals, that would produce hundreds of thousands, if not millions of baby corals that might help restore the reef that wouldn't otherwise be there," Baker said.

Oceans store heat

Even if scientists succeed in breeding more resilient coral, Baker said that would only buy a little more time for the world's reefs.

"Quite honestly, with the scale of the problem and the magnitude of the reef, these are all sort of drops in the bucket," he said. "Here's the thing that scientists have been saying is going to happen to reefs more and more often if we fail to do nothing. And what we really need to pay attention to is the root causes of climate change."

Those root causes include pumping the planet full of heat trapping carbon dioxide, mainly from the use of fossil fuels. As the planet has warmed, 90% of that heat has been trapped in the world's ocean. The last 10 years have been the ocean's hottest decade on record, with 2022 recording the highest global temperature.

That's not only bad news for ocean life like coral and shellfish struggling with increased ocean acidification from all the extra carbon, but also climate weather patterns and sea rise.