Murrumu of Walubara, right, snorkels with his son, Thoyo of Walubara, at the Great Barrier Reef in Australia last year. Surveys conducted by Brook Mitchell / The New York Times

Earlier this year, scientists warned that the Great Barrier Reef could be on the brink of its most widespread bleaching event ever recorded. That fear has been realized.

Surveys conducted by scientists at Australia’s James Cook University and the Great Barrier Reef Marine Park Authority show that a summer of extreme heat has caused the reef, which is a World Heritage Site, to suffer a mass bleaching of unprecedented scale. Corals from the far north to the southern tip of the 1,400 mile-long ecosystem are experiencing severe impacts.

It was also one of the reef’s worst mass bleaching episodes in terms of intensity, second only to 2016, which killed half of all shallow-water corals on the northern Great Barrier Reef.

Unlike the summer of 2016, when an intense marine heat wave coincided with one of the strongest El Niño events on record, this past summer brought a bleaching […]