Coral Bleaching Crisis Worsens Following Hottest Year Yet

According to scientific experts, over 80% of the world’s coral reefs have been severely affected by extensive bleaching events triggered by record-high ocean temperatures. This has caused many vibrant reefs to appear ghostly white.

Coral bleaching occurs when corals experience unusual increases in water temperature, prompting them to expel the colorful algae that reside within their tissues. These algae provide essential nutrients, and without them, corals are unable to survive.

The fourth global mass bleaching event, which scientists identified a year ago, shows no signs of abating, as reported by the International Coral Reef Initiative and the U.S. National Oceanic and Atmospheric Administration, who monitor reef health.

This event has escalated to the most extensive on record, with 84% of reef areas—from the Indian Ocean to the Atlantic and Pacific—experiencing intense heat stress, leading to expectations of bleaching as of March 2025.

Last year recorded the highest temperatures ever, surpassing pre-industrial levels by more than 1.5 degrees Celsius, which contributed to unprecedented ocean temperatures and a triple surge in marine heatwaves globally.

Melanie McField, a marine scientist in the Caribbean, stated, “The scale and reach of the heat stress are alarming. Some reefs previously considered to be resilient have suffered partial mortality in 2024.”

“The sight of bleaching is always unsettling—like a silent snowfall has blanketed the reef,” she added.

In the past, mass bleaching events in 1998, 2010, and 2014-2017 affected 21%, 37%, and 68% of reefs to varying degrees of heat stress, respectively.

Marine biologists had warned early last year that a mass bleaching crisis was imminent due to months of record-high ocean temperatures driven by human-induced climate change and the El Niño phenomenon, which typically raises ocean temperatures around the equator and Pacific.

A weak La Niña pattern in December 2024 offered hope for a coral recovery by cooling ocean temperatures, but this respite only lasted for three months.

Unfortunately, the bleaching continues to expand, according to Derek Manzello, coordinator of NOAA’s Coral Reef Watch. Recently, the Solomon Islands and Papua New Guinea joined the ranks of 82 countries and territories experiencing bleaching-level heat stress.

It will take researchers years to fully assess the global impact of coral reef mortality, but significant losses have already been witnessed in various areas, including parts of the Caribbean, the Red Sea, and Australia’s Great Barrier Reef.