TAMPA, Fla (WFLA) — “I have never been so worried for the future of Florida’s reefs.” This is the reaction of coral scientist Bill Precht to the record hot ocean temperatures surrounding South Florida right now.

Precht is a coral reef scientist based in Miami who’s been studying coral reefs for the past 45 years. WFLA’s Chief Meteorologist and Climate Specialist Jeff Berardelli spoke to Precht on Monday.

“Based on what I have seen throughout my career – and what I am seeing unfold so far this summer — if greater than 90% of what’s left gets whacked – there will essentially be nothing left,” Precht said, “This is the scary reality. This is not science fiction.”

Average coral cover on most Florida Keys reefs has dropped from between 30-50% before 1975, to less than 3% now. Precht says this is due to coral disease, coral bleaching events, hurricanes, and cold water impacts during the winter. What’s left has been significantly weakened.

“Right now, I’d say the corals in the Florida Keys are as vulnerable as they have ever been to catastrophic levels of bleaching and bleaching-related mortality,” Precht warns.

Coral thrives in a fairly narrow range of water temperatures which, Precht says, rarely exceeded 84 degrees a century ago. Now, due to man-made climate heating, regularly rise into the upper 80s.

But right now water temperatures are even higher, averaging around 90F, with some pockets as high as 95, or an outlandish 97. Even for a hot place like South Florida in July, this is “off the charts”.

This graph below from NOAA Coral Reef Watch shows sea surface temperatures in the Florida Keys since 1985. The black line shows the average regional water temperature for 2023, which right now is around 90 degrees Fahrenheit (32 degrees C), far above the average of 84F.

WFLA Chief Meteorologist and Climate Specialist Jeff Berardelli spoke to the Coordinator of NOAA Coral Reef Watch, Dr. Derek Manzello. He says this chart “illustrates that the sea surface temperatures are hotter than they have ever been in the satellite record for this early in the year.” In fact, it’s about as hot as has ever been measured any time of the year.

Image: NOAA Coral Reef Watch

But it’s not just hot water that has Manzello and Precht so concerned. It’s that the record heat is happening so early in the summer and we are still several weeks away from the typical peak heating.

“We are a full month ahead of what is the normal ‘bleaching season’, Manzello explains.  “What this means is, unless significant cooling takes place (e.g., repeat passage of hurricanes or tropical storms), the corals of the Florida Keys may be looking at upwards of 3 consecutive months of thermally-stressful conditions, which would be unprecedented. Most previous bleaching events lasted about 4-6 weeks.”

And that’s the problem. It’s not just the heat, it is the ‘relentless’ heat that can take a deadly toll – the accumulated heat stress. When corals get stressed by warm water, they turn white (bleach) as they expel the colorful algae living in their tissues. If the heat lasts long enough the coral can die. That’s why Precht says this summer may be the “death knell” for South Florida coral.

University of Miami Researcher Brian McNoldy keeps a close track of South Florida weather metrics. He does not recall ever seeing anything like this.

This marine heatwave surrounding Florida is due to a very unusual recent weather pattern on top of the long-term trend of human-caused climate heating.

Over the past few decades, water temperatures have increased by an average of a couple of degrees (Fahrenheit) in the Atlantic Basin due to human-caused greenhouse warming. That’s because nearly 90% of excess heat from climate change is stored in the ocean. Globally major ocean heatwaves have become 20 times more common.

This trend in heating, coupled with reduced atmospheric pollution which allows more sunlight in, has steadily heated the water over the past few decades. Thus the baseline temperature has increased.

On top of that, in the short term, Florida’s weather pattern has been very unusual since late spring. Typically high pressure builds in from the Atlantic during the rainy season, spreading breezy east to southeast winds across the state. But the Atlantic high pressure has failed to nose into Florida this summer, leading to weak winds and stagnation across South Florida.

Generally, this weaker high pressure, and the weaker winds associated with it, are prevalent across the Atlantic Basin this summer.

Without winds to churn up the water column, South Florida water temperatures have continued to rise. The map below shows where water temperatures exceed 90 degrees Fahrenheit in magenta shading. While 90 is not abnormal for summer in the shallows off the beaches of the Tampa Bay Area, it is extreme for the Florida Keys which are adjacent to very deep, cooler waters.

Image: WFLA. Sea surface temperatures July 10th 2023. Areas in Magenta are above 90 degrees Fahrenheit.

In Central Florida and the Tampa Bay area, the prevailing pattern has brought consistent light westerly winds for a rare, if not unprecedented, several weeks since the rainy season has begun. For Florida’s West Coast, this has led to low cloud cover and very little rainfall, heating sea surface temperatures.

When asked if the reefs off the Tampa Bay area (which are deeper than many in the Keys) may suffer this year, Precht said, “I do believe some of the hardbottom ecosystems on Florida’s West Coast may see coral bleaching as well this summer.”

Over the next ten days, not much is expected to change weatherwise across the state. Thus the hot water is forecast to persist. And unless a prolonged stormy or windy pattern evolves or a tropical system moves through over the coming weeks, not much will change. The following Twitter thread explains the mechanisms at play in detail.

Putting this into a larger perspective, the Atlantic Ocean and global ocean temperatures have been far above record levels for months now. This is partly due to El Niño, a natural cyclical warming of the eastern Tropical Pacific waters, which releases excess heat into the climate system.

Image: WFLA Sea Surface Temperature Anomalies July 10th 2023

As a result of this developing strong El Niño, on top of global warming, global surface temperatures reached record heights not seen in 120,000 years last week.

As we head further into summer, and Northern Hemisphere oceans reach their peak heating, NOAA forecasts that 50% of global oceans will experience marine heatwave conditions by September. That area is made two times larger than it would have otherwise been before humans started warming the Earth.

As a result of the record warm oceans, NOAA’s coral bleaching forecast in the Caribbean this summer is extensive, with most places near 100%.

“Throughout my entire career, I have been an eternal optimist, believing that corals, and coral reefs could be protected and restored from the onslaughts of man,” Precht explains. “However, the recent maladies facing most reefs around the world, including those in Florida, have not been associated with local sources of stress or pollution, but have been directly caused by or associated with global warming and global climate change.” 

“No form of management or protection can prevent reefs from being impacted by increases in sea surface temperatures associated with the burning of fossil fuels,” Precht says with regret.   “Local management actions can do little to stop a coral bleaching event, or a coral disease outbreak, or the impacts of a catastrophic hurricane that has grown larger because of climate change.”