An exhaustive aerial survey of the Great Barrier Reef is revealing that a huge swath is severely bleached - and that the damage is far worse than some officials thought. 

"We're seeing huge levels of bleaching in the northern thousand-kilometer stretch of the Great Barrier Reef," said coral reef expert Professor Terry Hughes of James Cook University in Townsville, in an interview with the ABC's 7:30. 

Professor Hughes led the team which used used charter planes and helicopters to conduct an aerial survey of the reef.  The team found that as much as 95 percent of the northern section of the Reef is "severely bleached" - in fact, only four out of 520 corals showed no signs of bleaching.  Their survey area spanned 100,000 square kilometers.  Hughes says unlike past events, this will change the Reef forever.

The cause is clear: Global warming. 

"What we're seeing now is unequivocally to do with climate change," said Professor Justin Marshall, a reef scientist from the University of Queensland.  "The world has agreed, this is climate change, we're seeing climate change play out across our reefs," he added.

Dr. Mark Eakin, the Coordinator of the US National Oceanic and Atmospheric Administration's Coral Reef Watch says Australia "may lose half of their healthiest corals" to what he says is "the worst bleaching ever seen on what was the healthiest part of the Great Barrier Reef".  He had two words to describe the situation:  "Very dire".  

The fact is, the Great Barrier Reef is just one of several of the world's coral reefs that are so stressed that some fear that we may be seeing the end of coral, that this kind of ecosystem is dying out. 

"For the rest of the world, this event is nowhere near over," said Dr. Eakin.  "Right now there is bleaching across half the southern hemisphere - literally.  It spans from the coast of Tanzania in the west to French Polynesia in the east.  Reports are coming in this week of bleaching throughout Indonesia."  The inshore reefs of New Caledonia are also in deep trouble, as are those in Kiribati.  Florida may be headed into a third year of bleaching.

But this wasn't unexpected.  The scientists have been trying to warn the government for two decades.

"The government has not been listening to us for the past 20 years," lamented Professor Hughes.  "It has been inevitable that this bleaching event would happen, and now it has.  We need to join the global community in reducing greenhouse gas emissions."