More than three-quarters of the world’s reefs have been subjected to catastrophic mass bleaching, stimulated by record ocean temperatures, which has turned many of the once-colored reefs into ghostly pale tones, scientific authorities said Wednesday.
Bleaching is caused by abnormalities in water temperature, causing the corals to discharge colorful algae to live in the tissues. Corals will not survive without the help of algae feeding nutrients into the corals.
According to the International Coral Reef Initiative and data from the National Oceanic and Atmospheric Administration, this is the fourth world’s massive bleaching event announced a year ago, showing little signs of slowing down.
Instead, it has become the most extensive on record, with 84% of the reefs (from the Indian Ocean to the Atlantic Ocean to the Pacific) suffering severe heat stress for the duration of March 2025 to March 2025.
Last year was the hottest person on record, the first to reach 1.5 degrees Celsius over 1.5 degrees Celsius from the pre-industry period, which led to unprecedented ocean temperatures and three times the number of ocean heat waves recorded in the last century.
“The magnitude and extent of thermal stress is alarming,” said Melanie McField, an ocean scientist working in the Caribbean. “Some reefs have escaped severe thermal stress so far, and we think they are somewhat resilient to some extent, succumbing to partial death in 2024.”
“Bleaching is always creepy – as if the quiet snowfall is falling on the reefs,” she added.
In 1998, 2010 and 2014-17 events were 21%, 37% and 68% of reefs suffered from bleaching grade heat stress, respectively.
Marine biologists warned early last year that coral reefs in the world are on the verge of massive bleaching, which produce unusually warm ocean temperatures along the equator and the Pacific region, due to the climate change caused by humans and the climate patterns of El Nino.
In December 2024, a weak La Nina model usually brings colder ocean temperatures, making scientists hope that the corals will recover, but lasted only three months.
Instead, bleaching continues to spread, said Derek Manzello, coordinator of NOAA Coral Reef Watch. The Solomon Islands and Papua New Guinea were recently added to 82 countries and regions, registering bleach-grade heat stress in their waters.
To understand the global scope of coral reef deaths, scientists will take several years, but they say they have observed widespread mortality rates in parts of the Caribbean, the Red Sea and Australia’s Great Barrier Reef.
