‘Literally off the charts’: global coral reef heat stress monitor forced to add new alerts as temperatures rise

Last year in the northern hemisphere summer, large areas of coral reef across several countries experienced heat stress well beyond the highest existing rating. Photograph: Joseph Prezioso/AFP/Getty Images

The world’s main system for warning about heat stress on the planet’s coral reefs has been forced to add three new alert categories to represent ever-increasing temperature extremes.

The changes introduced by the US government’s Coral Reef Watch program come after reefs across the Americas were hit by unprecedented levels of heat stress last year that bleached and killed corals en masse.