The world's coral reefs suffer a global mass bleaching

The world's coral reefs suffered a global mass bleaching event this year, as record-breaking ocean temperatures triggered widespread coral bleaching across reefs in every major ocean, in only the fourth such planet-wide event ever recorded.

Scientists confirmed that bleaching had been documented across a vast swath of the world's reefs, from the Great Barrier Reef and the wider Pacific to the Caribbean, the Indian Ocean and the Red Sea, as marine heat waves of unprecedented intensity and extent stressed corals around the globe.

Coral bleaching occurs when heat-stressed corals expel the symbiotic algae that nourish them and give them colour, turning white and, if the stress persists, dying. A global bleaching event, affecting reefs across multiple ocean basins, is a sign of the extraordinary scale of the ocean warming under way.

Coral reefs are among the most biodiverse ecosystems on the planet, supporting a quarter of all marine species and underpinning the food security and livelihoods of hundreds of millions of people, as well as protecting coastlines from storms. Their decline is both an ecological catastrophe and a human one.

Scientists warned that reefs are among the ecosystems most immediately threatened by climate change, and that even the more optimistic warming scenarios could see the vast majority of coral reefs lost. The global bleaching event was a dire warning of the toll that a warming ocean is taking beneath the waves, and of the urgent need to curb the emissions driving it before the world's reefs are pushed past the point of no return.