Two-thirds of Great Barrier Reef damaged in ‘unprecedented’ bleaching

Coral bleached for two consecutive years at Australia's Great Barrier Reef has "zero prospect" of recovery, scientists warned Monday, as they confirmed the site has again been hit by warming sea temperatures.

Researchers said last month they were detecting another round of mass bleaching this year after a severe event in 2016, and their fears were confirmed after aerial surveys of the entire 2,300-kilometre  long bio-diverse reef.

Last year, the northern areas of the World Heritage-listed area were hardest hit, with the middle-third now experiencing the worst effects.

"Bleached corals are not necessarily dead corals, but in the severe central region we anticipate high levels of coral loss," James Kerry, a marine biologist at James Cook University who led the aerial surveys, said.

"It takes at least a decade for a full recovery of even the fastest growing corals, so mass bleaching events 12 months apart offer zero prospect of recovery for reefs that were damaged in 2016."

He described the damage as “unprecedented.”

Prof Terry Hughes, head of the Centre of Excellence for Coral Reef Studies at James Cook University, said governments must urgently address climate change to prevent further bleaching.

"Since 1998, we have seen four of these events and the gap between them has varied substantially, but this is the shortest gap we have seen," Prof Hughes told the BBC.

"The combined impact of this back-to-back bleaching stretches for 1,500 kilometres, leaving only the southern third unscathed," Hughes said.

"The bleaching is caused by record-breaking temperatures driven by global warming. This year, 2017, we are seeing mass bleaching, even without the assistance of El Nino conditions," he added, referring to the natural climate cycle in the Pacific Ocean.

This is the fourth time coral bleaching has hit the reef after previous events in 1998 and 2002.

The reef - a vast collection of thousands of smaller coral reefs stretching from the northern tip of Queensland to the state's southern city of Bundaberg - was given World Heritage status in 1981.