Half of Great Barrier Reef coral now 'dead or dying', say scientists

Australian scientists said on Wednesday that just 7 percent of the Great Barrier Reef, which attracts around $3.90 billion in tourism every year, has been untouched by mass bleaching that is likely to destroy half the coral.

Bleaching occurs when the water is too warm, forcing coral to expel living algae and causing it to calcify and turn white. Mildly bleached coral can recover if the temperature drops, otherwise it may die.

Although the impact has been exacerbated by one of the strongest El Nino weather systems in nearly 20 years, scientists believe climate change is the underlying cause.