'Should Be a Global Wake-Up Call': Coral Reefs Suffer Fourth Mass Bleaching Event

Scientists said Monday that the world's coral reefs are facing a fourth global bleaching event as the fossil fuel-driven climate emergency pushes ocean temperatures to record highs, imperiling the critical underwater ecosystems that sustain thousands of species.

The National Oceanic and Atmospheric Administration (NOAA) and the International Coral Reef Initiative (ICRI)—which NOAA co-chairs—said they documented coral bleaching in the northern and southern hemispheres of every major ocean basin on Earth between February 2023 and April of this year. It could be the worst global bleaching event on record.

"Since early 2023, mass bleaching of coral reefs has been confirmed throughout the tropics including Florida in the U.S.; the Caribbean; Brazil; the eastern Tropical Pacific (including Mexico, El Salvador, Costa Rica, Panama, and Colombia); Australia's Great Barrier Reef; large areas of the South Pacific (including Fiji, Vanuatu, Tuvalu, Kiribati, the Samoas, and French Polynesia); the Red Sea (including the Gulf of Aqaba); the Persian Gulf; and the Gulf of Aden," the organizations said in a statement.

"NOAA has received confirmation of widespread bleaching across other parts of the Indian Ocean basin as well, including in Tanzania, Kenya, Mauritius, the Seychelles, Tromelin, Mayotte, and off the western coast of Indonesia," they added.

"More than half the reefs on the planet have basically experienced bleaching-level heat stress in the last year."

Derek Manzello, coordinator of NOAA's Coral Reef Watch, said that "as the world's oceans continue to warm, coral bleaching is becoming more frequent."

Excessively warm water causes corals to expel algae from their tissues, causing the organisms to turn white. While they can recover, such bleaching is evidence that corals are under significant stress and at risk of death.

The latest global bleaching event is the second in the last 10 years and "should be a global wake-up call," Manzello toldThe Washington Post.

"More than half the reefs on the planet have basically experienced bleaching-level heat stress in the last year," said Manzello.

NOAA and ICRI's statement comes as scientists around the world are voicing growing alarm over high ocean temperatures. Research released last month showed that global ocean surface temperatures had broken records every day of the year up to that point, underscoring the need to aggressively rein in fossil fuel production and use.

"Temperatures are off the charts," Emily Darling, director of coral reefs at the Wildlife Conservation Society, said Monday. "While many corals are suffering from extreme heat stress and bleaching, some locations and species show different types of natural resilience. Finding and conserving these priority coral reefs are critical to any global strategy to safeguard the planet's oceans and blue economies."

"The announcement of the fourth global bleaching event is an urgent call to do two things: reduce greenhouse gas emissions and work together to prioritize resilient coral reefs for conservation," Darling added.