Once I would have thought that a ridiculous question. Yet today, if we assemble all the best science we have, the answer can at best be “maybe”.

It may seem preposterous that the greatest coral reef in the world – the biggest structure made by life on Earth – could be seriously (I mean genuinely seriously) threatened by climate change. The question itself is probably already relegated in your mind to a ‘here-we-go-again’ catch-bag of greenie diatribe about the state of our planet. This view is understandable given that even a decade ago, there were many scientists who had not yet come to grips with the full implications of climate change.

Very likely you have a feeling that dire predictions about anything almost always turn out to be exaggerations. What you really think is: OK, where there’s smoke there’s fire, so there’s probably something in this to be worried about, somewhere. But, it won’t be as bad as those doom-sayers are predicting. When I started writing “A Reef in Time”, I knew that climate change was likely to have serious consequences for coral reefs, but even I was shocked to the core by what all the best science that existed was saying. In a long phase of personal anguish I turned to specialists in many different fields of science to find anything that might suggest a fault in my own conclusions. No luck. The bottom line remains: the GBR can indeed be utterly trashed in the lifetime of today’s children. That certainty is what motivates me to broadcast this message as clearly, as accurately and, yes, as loudly, as I can.

So, what are the issues? You probably know that there have been several major episodes of mass bleaching on the GBR over the past 20 years and that these have been caused by pulses (El Niño events) of warm surface water heated by the greenhouse effect. The basic numbers showing the relationship between damage and temperature are there for all to see. There is no escaping the prediction that the worse bleaching year we have had to date will be an average year by 2030 and a good year by 2050. You don’t even need a pocket calculator to conclude that the only corals left alive by then will be those hiding in refuges such as deep outer reef slopes.

What you may not know is that bleaching is only of minor concern compared to a much more insidious and devastating issue looming in the background – ocean acidification.

Put simply, the carbon dioxide we are producing is readily absorbed by water and turned into carbonic acid which is taken up by the oceans and neutralized by carbonate/bicarbonate buffers. The problem is that we are now producing carbon dioxide so rapidly that this process is actually changing the chemistry of ocean water, making it less alkaline and altering the saturation state of the buffers. A small matter you might think, but it isn’t. Changes are already being recorded in the Southern Ocean (gases are more readily absorbed in cold water so colder oceans will show changes first), a process that will reach the equator at about the same time as the interval mentioned above: about 2030 with full effects by 2050. Sod’s law will then apply: the coral refugees from temperature will be the most affected by acidification. Ocean chemistry is a well-understood subject and acidification is progressing in a way that is easily predicted from a few simple chemical equations. Although much is not yet well understood about the responses of species to marginal conditions, we do know that corals and plankton cannot build normal skeletons under the acidification that is predicted; they will suffer what can aptly be described as coralline osteoporosis. Nor is there time for them to evolve solutions. That means that they will neither build reefs nor be able to maintain them against the forces of erosion. What were once thriving coral gardens that supported the greatest biodiversity of our oceans will be red-black bacterial slime and they will stay that way. I have already worked in such places – there’s a photo of one in my book.

There is another frightening aspect of Climate Change. It is contained in the concept of ‘commitment’, a word we will soon be hearing only too often. In climate change speak this means the commitment of the Earth now to paths of change that will be unavoidable and unstoppable in the future. This delayed reaction is due to the inertia of the oceans, both thermal and chemical. Put another way, the greenhouse gases we are producing now will take a couple of decades to produce the changes they are destined to make. And when they do produce those changes they will be for keeps as far as humanity is concerned.

What I must make clear is that, great though the GBR is, if climate change can destroy one reef it can destroy them all. So let’s forget all those grandiose adjectives that are always used to describe our Great Barrier Reef. All coral reefs grow near the ocean surface and they will all be affected by changes to that surface. As the dinosaurs discovered, size offers no protection from an environmental upheaval. We are talking about a mass extinction event.

Mass extinction events – five in total – have hit coral reefs so hard they have taken at least four million years to re-evolve. Although we know little about the first mass extinction, the next four were primarily the result of massive climatic changes, with the carbon cycle convincingly implicated in all. What is the fast acting currency of the carbon cycle? Carbon dioxide. I can’t escape the bottom line which says we are setting conditions on Earth for the sixth great mass extinction. Coral reefs are the ocean’s canaries. They have now sounded their warning and have started leaving the same message they left in the past.

Certainly all past extinction events are associated with much higher levels of carbon dioxide than anything predicted today, but the rate of change we are experiencing now has no known precedent in all Earth history. It is not just ‘abrupt’ (as is often described), it is geologically and evolutionarily instantaneous. That is the big picture. In our here-and-now detail of it, another decade like our last will send the Earth across the tipping-point, and our children will see the results.

Climate change is the greatest challenge humanity has ever faced. On our present tack the future looks bleak, but it is far from hopeless. We have the science and technology to stop this from happening. What we must do now is buy enough time for this S&T to come to the rescue. We know how to cut emissions enough through individual and corporate actions alone, irrespective of intergovernmental undertakings. We just need to accept, at all levels, that the job has to be done. Then get on with it, and fast.