The plight of the Great Barrier Reef

Over the past decades there have been many stories in the media about the plight of the Great Barrier Reef.

In the '60s and '70s we all heard that the Great Barrier Reef was about to be consumed by that voracious predator, the Crown of Thorns Starfish.

In the '80s and '90s, the principal threats turned out to be sediment runoff, to nutrients, over fishing and general habitat destruction.

For me, an ancient marine scientist who has spent thousands of hours diving on the Great Barrier Reef these past 40 years, each of these threats has been of concern. But nothing comes close to the devastation waiting in the wings at the moment.

Very likely you have a feeling that dire predictions about anything almost always turn out to be exaggerations. This view is understandable. Once I also would have thought it ridiculous to imagine that the Great Barrier Reef might have a limited future as a consequence of human activity. It would have seemed preposterous that the greatest coral reef on Earth, the biggest structure made by life on Earth, could be mortally threatened by any present or foreseeable change.

I was wrong. Yet here I am today, utterly convinced that the Great Barrier Reef will not be there for our children's children to enjoy. Unless we dramatically and immediately change our priorities, and the way we live.

I have been immensely fortunate in my career to have worked on coral reefs around the globe. And to have worked in many different disciplines of science. I have had the opportunity to make a significant contribution to reef science, and to reef conservation. Now comes time for payback, for responsibility. Responsibility to speak out, on behalf of that life which cannot plead its own cause.

When I started writing my book, I knew that climate change was likely to have serious consequences for coral reefs. But the big picture which emerged, quite frankly, left me shocked to the core.

This really led to a period of personal anguish. I turned to specialists in many different fields of science to find anything that might suggest a fault in that big picture. I was depressingly unsuccessful. The bottom line remains: the combination of the best science today argues that the Great Barrier Reef can indeed be utterly trashed in the lifetime of today's children. That is what motivates me to broadcast this message as clearly, as accurately, and as far as possible.

So, what are the issues? You probably know that there have been several major episodes of mass bleaching on the Great Barrier Reef since this began in the late 1980s. Since then the frequency of bleaching events has increased, and this has sparked an intense research effort.

Corals have an intimate give-and-take symbiotic relationship with single-celled algae called zooxanthellae which live in their cells and provide most of the food they need. A lot of research has shown that this symbiosis can be surprisingly fragile. If corals are exposed to high light at the same time as high temperature, the algae produce toxic levels of oxygen. Corals must expel this zooxanthellae, bleach and probably die. Or succumb to the toxin and definitely die. A tough choice. It is one they are not designed to make.

As the greenhouse effect from elevated carbon dioxide has increased, the oceans have absorbed more and more greenhouse heat. The surface layers are being affected most, but large ocean areas have a temperature limit, about 31C. Once this limit is reached, the surface does not warm further, but it broadens and it deepens. This creates the largest mobile heat mass on earth.