Global Coral Bleaching Crisis ‘Spreads’ After Hottest Year

The coral reefs of the world continue to face an unprecedented threat as mass bleaching occurs on a previously unrecorded scale, driven by extreme ocean heat. Over 80% of the world’s coral reefs have now been affected, leaving many vibrant ecosystems strikingly pale and fragile.

Coral bleaching is primarily caused by prolonged heat stress, which leads to the expulsion of colorful algae residing within coral tissues. These algae are crucial for the coral’s survival as they provide them with vital nutrients. Without these algae, corals cannot maintain their vitality.

In the wake of the planet’s fourth mass bleaching incident, which was first identified last year, slowing down seems unlikely according to the latest research focusing on reef health. This recent event has now been recognized as the most extensive ever recorded. As of March 2025, 84% of coral reefs across the Indian Ocean, Atlantic Ocean, and Pacific Ocean have been under conditions conducive to bleaching.

The previous year broke records, becoming the warmest since the onset of industrialization, with temperatures surpassing 1.5 degrees Celsius above pre-industrial levels. This extreme warming has led to unmatched ocean temperatures and has tripled the historic number of marine heatwaves globally.

“The scale of the current thermal stress is overwhelming,” noted a marine scientist analyzing Caribbean reefs. “Coral formations thought to have been resilient to past heat events have experienced partial deaths this year.”

This widespread bleaching event follows earlier ones in 1998, 2010, and 2014-17, during which 21%, 37%, and 68% of reefs respectively encountered bleaching-level heat.

Marine biologists had alerted the global community early in the previous year that reefs were on the brink of a mass bleaching event, exacerbated by anthropogenic climate dynamics and the El Niño phenomenon, leading to unusually high temperatures across equatorial and Pacific waters. The brief period of La Niña conditions toward the end of 2024, which typically has a cooling effect, brought some optimism for coral recovery but was short-lived.

The bleaching process continued its advance despite these hopes, with regions like the Solomon Islands and Papua New Guinea now joining an alarming list of 82 nations enduring bleaching-level thermal conditions in their waters.

Understanding the full aftermath of coral mortality globally will require extensive research and years of study. Nevertheless, significant coral losses have already been documented in regions such as the Caribbean, the Red Sea, and Australia’s Great Barrier Reef.

As the temperatures continue to soar, the sprawling reefs face a dire prognosis without significant changes in ocean stewardship and climate mitigation strategies. Efforts to monitor, protect, and restore these vital ecosystems must now be prioritized more than ever.