TAMPA, Fla. (WFLA) — The summer of 2023 featured the most extreme and persistent marine heatwave ever recorded in South Florida and the Florida Keys.
Sea surface temperatures lingered in the low 90s and marine heatwave conditions lasted for more than 20 weeks, more than doubling the former record.
As a result, most of the already thin coral cover in the Florida Keys bleached, and a large percentage of that died.
Now a new study in Journal Science, co-authored by researchers at NOAA and the University of Queensland, finds that “climate change and its impact on coral reefs have reached unchartered territory.”
The report reveals alarming changes in the upper ocean’s conditions, ecosystems and communities, and finds that these changes, which trace back to the early 1980s when mass coral bleaching was first observed, strongly correlate with rising sea surface temperatures and climate cycles such as the El Nino Southern Oscillation (ENSO).
In the Florida Keys, water temperatures have risen 3 degrees Fahrenheit over the last 50 years, raising the base maximum summer temperatures from 84 degrees, which is tolerable for coral, to a deadly 87 degrees in recent years.
Corals are very sensitive to changes in water temperature. Bleaching occurs when corals stress due to warmer than normal water, turning the tissue white. If the warmth persists, it can often lead to death.
Bleaching events in the Florida Keys used to be very rare a few decades ago, but over the past decade, bleaching has occurred just about every year as water temperatures consistently reach or exceed tolerable levels.
This summer was by far the worst ever experienced, horrifying coral scientists, and it wasn’t just in South Florida. Global sea surface temperatures far exceeded previous records and those records are still being broken today.
In this week’s Climate Classroom, we are interviewing Derek Manzello, Ph.D., coordinator of NOAA’s Coral Reef Watch program in College Park, Maryland. He co-authored a recent study in Journal Science.
In response to this summer’s unprecedented event, Manzello said:
“Nearly all coral reef regions in the wider Caribbean, including Florida, were exposed to more than double the amount of heat stress that is expected to elicit mortality. The full ecological impacts of this event will not be fully realized for months to years, but preliminary reports have been alarming, as high levels of mortality in staghorn and elkhorn corals have already been reported in Florida, Puerto Rico and Mexico.”
But the impacts this year are not restricted to our part of the world. Due to a combination of human-caused climate heating and a strong El Nino, the heat is spreading.
“The trouble now is that impacts appear to be rolling into a vast, record-breaking global event,” warned William Skirving, Ph.D., a senior scientist at NOAA’s Coral Reef Watch.
Dr. Derek Manzello told WFLA’s Chief Meteorologist and Climate Specialist Jeff Berardelli that the 2023-2024 year is on the cusp of becoming a global event.
“We are more than likely just days to weeks away from this bleaching event officially becoming a global event. The SW Indian Ocean (as well as the SW Pacific) are heating up rapidly now. Bleaching level heat stress is already occurring near the Seychelles, Mauritius and Madagascar, thus it’s likely we are going to start receiving reports of bleaching very soon — when we receive reports from the Indian Ocean, then this event has officially gone global in scale.”
The authors of the report warn that the only way to stop tropical reefs from disappearing off the face of the Earth in a few decades is to stop the cause of this warming.
“These trends will worsen unless greenhouse gas (GHG) emissions decrease, with coral-dominated ecosystems likely to face substantial losses, leading to long-term damage to ecosystems and people across Earth’s tropical regions.”