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Environment, Science

Global science confirms the beginning of global coral bleaching event.

CMC 3 mins read

16 April 2024


According to NOAA scientists and colleagues, the world is currently experiencing another devastating global mass coral bleaching event. This is the fourth global bleaching event on record and the second in the last ten years.  

Bleaching-level heat stress, as remotely monitored and predicted by NOAA’s Coral Reef Watch (CRW), has been — and continues to be — extensive across the Atlantic, Pacific and Indian Ocean basins. CRW's heat-stress monitoring is based on sea surface temperature data, spanning 1985 to the present, from a blend of NOAA and partner satellites.


"From February 2023 to April 2024, significant coral bleaching has been documented in both the Northern and Southern Hemispheres of each major ocean basin," said Dr Derek Manzello, NOAA CRW coordinator.  Even the world’s most extensive continuous reef system – Australia’s Great Barrier Reef – has experienced unprecedented warming, with many corals dying.


Professor Ove Hoegh-Guldberg from the University of Queensland is also very concerned.


“Recent visits to sites in the southern and northern sections of the Great Barrier Reef reveal a common story:  The reef is now experiencing its fifth mass bleaching and mortality event in just nine years.”


Like many organisations on the ground, there is serious concern that conditions have changed, and coral reefs in places such as the Great Barrier Reef may rapidly disappear over the coming decade. 


Professor Hoegh-Guldberg said, “Reports are coming in thick and fast, making it clear that this is no ‘ordinary event’. It was the most widespread event on the Great Barrier Reef ever. And if that’s not enough, it is also the first time we have seen thermal stress values (Degree Heating Values, or DHW) reach a value of 16 or more. This means this is also the most intensive heat stress event on record.”


The situation is dire and is developing rapidly.

Since early 2023, mass bleaching of coral reefs has been confirmed throughout the tropics, including in 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.

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

“As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,” Manzello said. “When these events are sufficiently severe or prolonged, they can cause coral mortality, which hurts the people who depend on the coral reefs for their livelihoods.”


Coral bleaching, especially on a widespread scale, impacts economies, livelihoods, food security, but it does not necessarily mean corals will die. If the stress driving the bleaching diminishes, corals may recover, and reefs can continue providing the ecosystem services that people depend on.

“Climate model predictions for coral reefs have been suggesting for years that bleaching impacts would increase in frequency and magnitude as the ocean warms,” said Jennifer Koss, director of NOAA’s Coral Reef Conservation Program (CRCP).  


Because of this, the NOAA CRCP incorporated resilience-based management practices and increased the emphasis on coral restoration in its 2018 strategic plan, and funded a National Academies of Sciences’ study, which led to the publication of the 2019 Interventions to Increase the Resilience of Coral Reefs.  


Koss said, “We are on the frontlines of coral reef research, management and restoration and are actively and aggressively implementing the recommendations of the 2019 Interventions Report.”  


This global event requires global action. The International Coral Reef Initiative (ICRI), which NOAA co-chairs and its international members are broadly sharing and already applying resilience-based management actions and lessons learned from the 2023 marine heatwaves in Florida and the Caribbean. ICRI and its members are helping to advance coral interventions and restoration in the face of climate change by funding scientific research on best management practices and implementing its Plan of Action.


NOAA’s Coral Reef Conservation Program is a partnership across multiple NOAA offices and programs that brings together expertise for a multidisciplinary approach to understanding and conserving coral reef ecosystems.


Media contacts:

Professor Ove Hoegh-Guldberg,

Sean Kennedy, - +61 447 121 478

Contact details:

Sean Kennedy, - +61 447 121 378


Professor Ove Hoegh-Guldberg,

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