96% of coral reefs predicted to be critically endangered by 2075

Already, 24% of the world's shallow coral reefs are critically endangered. In October, the International Union for Conservation of Nature (IUCN) released its first global assessment of coral reef ecosystems. More than 250 experts studied shallow-water reefs in 127 tropical and subtropical regions, from Australia's Great Barrier Reef to the Coral Triangle in Southeast Asia. When the report added projected heat stress from climate change, it predicted that 96% of reefs will be critically endangered by 2075.

Heat stress drives decline

Heat stress from climate change is the most consistent threat driving reef decline worldwide. It causes coral bleaching, which happens when corals push out the algae living in their tissue. Those algae make most of the corals' food through photosynthesis. Without them, corals grow weak, become more open to disease, and can die.

Coral reefs cover less than 1% of the ocean floor, yet they support about 25% of marine life. Sarah Bedolfe, a senior marine scientist at the NGO Oceana who was not part of the assessment, said that if reefs collapse, the world could lose food, livelihoods and a lifeline for coastal communities.

Marcos Valderrábano, IUCN programme manager, said the biggest lever is cutting emissions and demanding urgent climate action. He added that corals also need better health to recover from heat waves. That means cutting pollution on reefs, protecting the corals that remain, and choosing sustainably caught seafood, since overfishing of parrotfish and grouper makes recovery harder. “None of this replaces emissions cuts,” he said.

The assessment says there is still time to head off complete ecological collapse of corals. Bedolfe said reefs are already declining, but their fate is not sealed. She said governments can ease pressure now by tackling overfishing and pollution, and by urgently cutting the greenhouse gas emissions that drive ocean warming.