How much coral was damaged by ocean heat?

A global bleaching crisis with large-scale ecological and economic stakes

Recent assessments show that extreme ocean temperatures have inflicted damage on coral reefs worldwide, with roughly half of the planet’s reef ecosystems hit hard during past heat waves. A separate, even more severe bleaching event is unfolding now, amplifying the threat to reef structure, biodiversity and the human communities that depend on them.

What happened and why it matters

• Heat stress: Prolonged, record-high sea surface temperatures disrupt the symbiosis between corals and the algae that supply them energy, causing the corals to expel their symbionts and turn white — a process known as bleaching. Repeated or prolonged bleaching can lead to widespread coral death.
• Ecosystem impacts: Reefs provide habitat, support fisheries and protect coastlines. Large-scale bleaching reduces fish populations, undermines livelihoods, and weakens natural coastal defenses against storms and erosion.
• Economic value: Coral ecosystems underpin substantial economic activity from tourism, fishing and coastal protection. Losses in reef health translate into direct and indirect costs for millions of people.

Looking ahead

Scientists warn that without rapid reductions in greenhouse-gas emissions and stronger local management to reduce pollution and overfishing, recovery windows for damaged reefs will narrow. Interventions being tested include assisted reef restoration, protecting refugia with naturally cooler conditions, and reducing local stressors to give corals a better chance to survive episodic heat. The picture is urgent: reefs are now experiencing repeated heat shocks that limit recovery time and increase the risk of long-term collapse across many regions.