Coral reefs no longer have time to recover, scientists warn of irreversible ocean changes

Coral reefs around the world are experiencing mass bleaching events with growing frequency, and the gaps between them have shrunk so much that reefs no longer have enough time to recover, according to a new international study. Researchers analyzed more than 40 years of data collected from nearly 37,000 coral reef sites across 120 countries and territories.

From decades to just a few years

In the past, major bleaching events could be separated by several decades. Now, the data show, they recur on average every five to six years. The main driver of bleaching is excessively high ocean water temperature: heat causes corals to expel the colorful algae living in their tissue that supply them with nutrients. As a result, corals turn pale and become far more vulnerable to disease. A bleached coral is not yet dead, but recovery requires both a drop in water temperature and sufficient time.

A rapid decline

The situation has worsened sharply in recent years. Between 2020 and 2024, the global amount of hard coral was 9.5% lower than historical norms. A bleaching event that began in 2023 turned out to be the most widespread ever recorded, affecting 77% of the world's coral reef areas. Scientists describe the process as a step-by-step decline — after each severe bleaching event, some corals manage to partially recover, but the next heat wave arrives before reefs can return to their previous state. With ocean temperatures still running high, another widespread bleaching event is possible as early as this year.

Why it matters

The loss of coral reefs would mean far more than a loss of natural beauty. Reefs provide habitat for roughly a quarter of all marine species, help protect coastlines, and supply food and livelihoods to millions of people worldwide. Scientists stress that rapidly cutting emissions, along with curbing local threats such as overfishing and excessive coastal development, could still help limit the damage already done to corals.