France, April 23 -- An unprecedented coral bleaching episode has spread to 84 percent of the world's reefs in an unfolding human-caused crisis that could kill off swathes of the essential ecosystems, scientists warned Wednesday.

Since it began in early 2023, the global coral bleaching event has mushroomed into the biggest and most intense on record, with reefs across the Pacific, Indian and Atlantic oceans affected.

Coral turns ghostly white under heat stress and the world's oceans have warmed over the last two years to historic highs, driven by humanity's release of planet-warming greenhouse gases.

Reefs can rebound from the trauma but scientists told AFP the window for recovery was getting shorter as ocean temperatures remained highe...