Climate change is blamed for the sea temperature rises that result in coral bleaching, and the consequences are clear. The recent El Niño-induced mass coral bleaching at the Great Barrier Reef threatens not only natural habitat but also the ecosystem's world heritage status, scientists have warned.

An aerial survey has revealed that the northern region of the world’s biggest reef system is undergoing the worst coral bleaching, affecting about 500 coral reefs spanning from Papua New Guinea to Cairns.

Ninety-five percent have already severely bleached, according to the team led by Professor Terry Hughes of the National Coral Bleaching Taskforce of Australia. Hughes considers the current event much worse than bleaching situations back in 1998 and 2002, with only four out of 520 reefs showing no evidence of bleaching.

Now, even the Great Barrier Reef’s world heritage status could be revoked. Last year, UNESCO decided not to include the reef on its “in danger” list. Concerned groups wanted this decision to be reassessed, but the UN body said it will be reviewed during its 2017 session.

When UNESCO made the decision to exclude the reef under this category, it sought an update from Australia regarding progress made in water and reef quality improvements. The federal government previously reported that the presently affected northern area of the reef was untarnished.

Richard Leck, national manager of World Wildlife Fund (WWF), which provides advice to the committee, warned that the severe bleaching puts the northern part of the reef in danger of coral mortality.

“I’m certain that UNESCO and the committee will be watching this disaster unfolding with great alarm,” he says.

WWF spokesperson Nick Heath also explains in a BBC report that the unspoiled northern part of the reef had served as a vital source for genetic material to reproduce further to the south. He adds that the bank had appeared resilient in past bleaching cases, yet now "cooked to an inch of its life." 

According to a spokesperson for environment minister Greg Hunt, the Australian government will update the world heritage center on its Reef 2050 Plan by the middle of 2017. As part of the usual five-year reporting cycle for these world heritage sites, the next conservation report will be reviewed by mid-2020s.