Coral reefs have always lived near the edge. Now, thanks to global warming, life there is five times more precarious.

Forty years ago, the world’s coral reefs faced a known risk: every 25 or 30 years, ocean temperatures would rise to intolerable levels.

Corals would minimise the risk of death by everting the algae with which they lived in symbiotic partnership: that is, the reef animals would avoid death by getting rid of the algae, deliberately weakening themselves.

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