The latest survey of the Great Barrier Reef off the coast of Australia reveals that an average of 35 percent of coral is now dead or dying in the northern and central sections. Experts from James Cook University say it’s the most extreme case of mass bleaching they have ever measured at the World Heritage Site.

So in the last 30 years or so, we’ve seen unprecedented episodes of mass bleaching that is very strongly linked to global warming.

And just describe specifically what happens then to the coral as the temperature in the water rises.

Here corals get most of their colour from the microscopic algae that live inside their tissues, the zooxanthellae. When the coral is stressed, the zooxanthellae die back. And because they give the coral most of its colour, when a coral is bleached, we can actually see the underlying carbonate skeleton underneath the tissue. A bleached coral is a very sick coral because they are compromised nutritionally because they get most of their energy from photosynthesis by the algae.

And how serious is the situation in the Great Barrier Reef?

Severely bleached corals can die. And right now on the Great Barrier Reef, we’ve seen unprecedented levels of coral mortality in the northern third of the Great Barrier Reef. So we estimate that in the top half of the Great Barrier Reef on average, 35 percent of the corals are dead or dying. It’s much less than that in the middle and southern section of the Great Barrier Reef. So in the north, many of the reefs we’ve surveyed have already lost half of their coral cover.

And in the context of the Great Barrier Reef, how much of it is the responsibility of the Australian government?

Well, the Australian government is responsible for stewardship of the Great Barrier Reef. There has been some progress recently in dealing with issues like fishing pressure and with water quality, but not at all really with climate change. So Australia is hardly leading the world in terms of its greenhouse gas emissions which are pretty much stable. Over recent years they haven’t yet declined. Australia recently issued a permit for a new coal mine through the next 60 years. That coal mine, if it goes ahead, would be the largest coal mine in the world.