Global Coral Bleaching Event Now Largest on Record, NOAA Says

At least 74 countries have been experiencing mass bleaching of coral reefs since early 2023 in response to rising ocean temperatures. 

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The current mass coral bleaching event affecting dozens of countries worldwide is now the largest event ever recorded, scientists have confirmed.

The National Oceanic and Atmospheric Administration (NOAA) in April declared that the world was undergoing its fourth global bleaching event, the second in the past ten years. At the time, at least 53 countries had been experiencing mass bleaching. The number has since gone up to 72.

This is the largest mass bleaching event on record, the US agency told Reuters last week. Satellite images revealed that a staggering 77% of the world’s coral reefs have been affected by bleaching across all the regions where warm-water corals live: the Pacific, Atlantic, and Indian Oceans in both the Northern and Southern Hemispheres.

“This event is still increasing in spatial extent and we’ve broken the previous record by more than 11% in about half the amount of time,” said NOAA Coral Reef Watch coordinator Derek Manzello. “This could potentially have serious ramifications for the ultimate response of these reefs to these bleaching events.”

Coral bleaching occurs as a heat stress response from rising ocean temperatures, which drives algae away from coral reefs, causing reefs to lose their vibrant colours. While a bleaching event is not directly linked to corals’ death, more frequent and intense heat stresses make corals more vulnerable to diseases, slowing down their recovery and limiting their ability to spawn.

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

Disappearing Ecosystems

Coral reefs are extremely important ecosystems that exist in more than 100 countries and territories and support at least 25% of marine species; they are integral to sustaining Earth’s vast and interconnected web of marine biodiversity and provide ecosystem services valued up to $9.9 trillion annually. They are sometimes referred to as “rainforests of the sea” for their ability to act as carbon sinks by absorbing the excess carbon dioxide in the water. 

Unfortunately, reefs are disappearing at an alarming pace. According to the most recent report by the Global Coral Reef Monitoring Network (GCRMN), the world has lost approximately 14% of corals since 2009. 

While coral bleaching can be a natural process that occurs due to rising oceans temperatures in the summer months or during natural weather phenomena such as El Niño, a rise in marine heatwaves linked to human activities has led to more frequent and larger bleaching events globally.

One of the best examples of coral bleaching is the Great Barrier Reef, the world’s largest and longest reef system located off the coast of Queensland, Australia; it covers about 350,000 square kilometres – an area that is larger than the UK and Ireland combined. The stunning coral reef system has already suffered six mass bleaching events in 1998, 2002, 2016, 2017, 2020, and 2024. The events in 2016 and 2017 were so severe that they led to the death of 50% of the iconic reef.

Aside from Australia, coral death has been particularly pronounced in regions such as South Asia, the Pacific, East Asia, the Western Indian Ocean, The Gulf, and Gulf of Oman.

“News of the largest coral bleaching event ever recorded is a devastating warning of what lies ahead,” said Kathryn Matthews, Chief Scientist at Oceana, a non-profit ocean conservation organization. “Without urgent action, we face not only the loss of these vital marine habitats but also the livelihoods and resources they provide for communities worldwide.”

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