Watch | Biggest ever coral die-off on Australia’s Great Barrier Reef

Warm seas around Australia's Great Barrier Reef have killed two-thirds of a 700-kmstretch of coral in the past nine months. It is the worst die-off ever recorded on the World Heritage. The Barrier Reef is UNESCO's World Heritage Site and the biggest is coral reef in the world. Due to global warming coral begin to bleach forcing coral to expel living algae and causing it to calcify and turn white. It'll take 10 to 15 years for a decent amount of corals to occur in those reefs again.