World's reefs under threat as coral bleaching intensifies

More than 80% of the world's coral reefs have suffered from severe mass bleaching due to unprecedented ocean temperatures, according to scientific authorities.

This phenomenon, characterised by corals expelling the vibrant algae crucial for their survival, has resulted in many reefs losing their once-vibrant colours, leaving them ghostly pale.

The ongoing fourth mass bleaching event, confirmed by the International Coral Reef Initiative and the United States National Oceanic and Atmospheric Administration, shows alarming signs of persistence.

As of March 2025, a staggering 84% of reef areas across the Indian, Atlantic, and Pacific Oceans have experienced intense heat stress, making it the most extensive bleaching event on record.

Last year was the hottest on record and the first to reach over 1.5 degrees Celsius warmer than pre-industrial times, contributing to unprecedented ocean temperatures and triple the previous record number of marine heatwaves around the world.

"The magnitude and extent of the heat stress is shocking," said Melanie McField, a marine scientist working in the Caribbean. "Some reefs that had thus far escaped major heat stress and we thought to be somewhat resilient, succumbed to partial mortalities in 2024."

"Bleaching is always eerie - as if a silent snowfall has descended on the reef," she added.

Previous events in 1998, 2010, and 2014-17 saw 21%, 37% and 68% of reefs subjected to bleaching-level heat stress respectively.

Marine biologists had warned early last year the world's reefs were on the verge of a mass bleaching following months of record-breaking ocean heat fuelled by human-induced climate change and the El Nino climate pattern, which yields unusually warm ocean temperatures along the equator and in the Pacific.

In December 2024, a weak La Nina pattern, which typically brings cooler ocean temperatures, gave scientists hope that corals might recover, but it only lasted three months.

Instead, the bleaching has continued to spread, said the NOAA Coral Reef Watch coordinator Derek Manzello. The Solomon Islands and Papua New Guinea were recently added to the list of 82 countries and territories registering bleaching-level heat stress in their waters.

It will take scientists years to understand the global extent of coral reef death, but they say they have already observed widespread mortality in parts of the Caribbean, Red Sea, and along Australia's Great Barrier Reef.