Australia's Great Barrier Reef has experienced its most widespread bleaching event on record, with the south of the reef bleaching extensively for the first time, a new survey has found, CNN reports.

This marks the third mass bleaching event on the reef in just the last five years and scientists say that the rapid warming of the planet due to human emissions of heat-trapping gases are to blame.

Aerial analysis conducted by Terry Hughes, director of the ARC Center of Excellence for Coral Reef Studies at James Cook University, and others from the Great Barrier Reef Marine Park Authority, found that coastal reefs along the entire length of the iconic reef — a stretch of about 1,500 miles (2,300 kilometers) from the Torres Strait in the north, right down to the reef's southern boundary — have been severely bleached.

"We are all in shock really at how quick this has happened," said Hughes. "Three severe bleaching events in five years is not something we anticipated happening until the middle of the century."

Warm ocean temperatures are the main driver of coral bleaching, which is when corals turn white as a stress response to water that is too warm. This happens because they are expelling the algae that grows inside them, which is their main energy source and gives them their color.

Bleaching doesn't kill coral immediately. But if temperatures remain high, eventually the coral will die, destroying a natural habitat for many species of marine life.