Heart Reef in The Great Barrier Reef, off Queensland, Australia, is the largest coral reef in the world.

Parts of Australia’s Great Barrier Reef face permanent destruction if the current El Niño, one of the strongest in two decades, does not ease this month, scientists said yesterday.

The El Niño is a result of a warming of the ocean in the western Pacific –ideal conditions for coral bleaching, where coral expels living algae, causing it to calcify.

Coral can only survive within a narrow band of ocean temperature.

The scientists said areas of the Great Barrier Reef, a world heritage site, are experiencing the worst bleaching in 15 years.

Coral around Lizard Island off the tropical city of Cairns has seen the most widespread bleaching, with 80 per cent of its coral bleached under unrelenting sunlight, Anne Hoggett, director, Lizard Island Research Station said.

“Bleaching is a clear signal that living corals are under physiological stress. If that stress is bad enough for long enough, the corals can die,” said Russell Reichelt, chairman of the Great Barrier Reef Marine Park Authority.

“What happens now will be entirely dependent on local weather conditions,” said Reichelt.

Scientists said the Great Barrier Reef needs a break in El Niño conditions within weeks if some coral areas areto survive.

The Australian Bureau of Meteorology’s most recent forecast calls for a continuation of El Niño conditions.

This year will be the hottest on record due to the El Niño weather pattern, according to the World Meteorological Organisation.

The Great Barrier Reef stretches 2,000 kilometres along Australia’s northeast coast and is the world’s largest living ecosystem. It brings in billions of dollars a year in tourism revenue.

Unesco’s World Heritage Committee last May stopped short of placing the Great Barrier Reef on an “in danger” list, but the ruling raised long-term concerns about its future due to climate change.

The El Niño is set to ease by the middle of 2016, according to the BOM.

But the weather system – which brings hot, dry conditions to Australia’s east coast – is seen as foreshadowing the likely impact of future climate change.

“Coral is the canary in the mine,” said Hoggett of the looming threat from climate change.