The World’s Fourth Mass Coral Bleaching Event Is Underway—and It Could Become the Worst One Yet

The impacted reefs represent 54 percent of the planet’s total, and that figure is currently increasing by 1 percent each week, NOAA scientists say

Bleached white corals in the Great Barrier Reef
Bleached corals in the Great Barrier Reef during a previous mass bleaching event. Brett Monroe Garner via Getty Images

Reefs and coastlines around the world are losing their color, as the fourth global coral bleaching event in recorded history is now underway, the National Oceanic and Atmospheric Administration’s (NOAA) Coral Reef Watch announced this week. The event further endangers the world’s already at-risk corals and the communities that live with them.

On the heels of ten consecutive record-breaking months of global air temperature, ocean heat is hitting alarming extremes in 2024. And when it comes to sea surface temperature, not a single day this year has been cooler compared to the 2023 calendar, which easily broke records.

Among the most vulnerable organisms to this change are the world’s corals. When faced with heat stress, they expel the colorful, photosynthetic algae they need to survive, turning a ghostly white in a process known as bleaching. In this state, corals are more vulnerable to starvation, disease and death, though bleaching can be undone if environmental extremes quickly return to normal.

The grave concern today: conditions are getting worse, experts say.

“I do get depressed sometimes, because the feeling is like, ‘My God, this is happening,’” Ove Hoegh-Guldberg, a climatologist at the University of Queensland in Australia, tells the New York Times Catrin Einhorn. “Now we’re at the point where we’re in the disaster movie.”

Since February 2023, more than 54 percent of the world’s coral reefs have experienced heat-induced bleaching—and this figure is currently increasing by about 1 percent each week, as Derek Manzello, coordinator of NOAA’s Coral Reef Watch, tells the New York Times.

The previous three mass coral bleachings occurred in 1998, 2010 and between 2014 and 2017. During these events, respectively, 20 percent, 35 percent and 56 percent of the world’s reefs were affected, writes the Guardian’s Graham Readfearn. If current trends continue, the new bleaching event could become the largest ever.

Coral bleaching has been documented across at least 53 countries and territories in the Pacific, Atlantic and Indian oceans and across both hemispheres. Some of the world’s largest and most precious reefs are being hit the hardest. For the first time ever, all three areas of the Great Barrier Reef Marine Park—for which this is the fifth mass bleaching event since 2016—are experiencing high levels of bleaching simultaneously, reports BBC News Georgina Rannard. And scientists at coastlines in Florida, the Caribbean, Costa Rica, Tanzania, Kenya, the Red Sea, the Persian Gulf and Indonesia—among many other places—are observing corals lose their color.

“A realistic interpretation is that we have crossed the tipping point for coral reefs,” David Obura, an ecologist who leads CORDIO East Africa, a coral reef research and conservation organization, tells Reuters Gloria Dickie and Alison Withers. “They’re going into a decline that we cannot stop, unless we really stop carbon dioxide emissions.”

A white coral in the foreground, with a healthy brown coral behind it.
A bleached coral, with a healthier coral behind it. Currently, corals in at least 53 countries and territories have experienced mass bleaching since February 2023. Wikimedia Commons under CC BY 3.0

The decline of reefs constitutes not only an environmental and cultural loss, but a financial one as well. Coral reefs help drive a $2.7 trillion global economy by supporting tourism, fisheries and coastal protections against storms. Reefs’ disappearance would have profound effects on tens of millions of people who rely on the ecosystems for their livelihoods.

Since 1950, Earth has lost half of its coral reefs. And if global air temperatures reach 2 degrees Celsius (3.6 degrees Fahrenheit) of warming compared to pre-industrial levels, scientists project a 99 percent decline in the world’s coral. Under a high-emissions scenario, this point is expected to be reached by 2050 or sooner.

“If given a chance, coral are actually resilient and can recover,” Emma Camp, a marine biologist at the University of Technology Sydney, tells BBC News. “But as bleaching becomes more frequent and stronger in intensity, we’re really narrowing that window.”

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