’Coral reefs… once survived in a world where CO2 from volcanoes and methane was much higher than anything predicted today.’ That sounds like good news from John Veron, a world authority on coral. Not if you read on: ’But that was over 40 million years ago, and the increase took place over millions of years, not just a few decades, time enough for ocean equilibration to take place and marine life to adapt.’
Veron is writing in an article recently published at Yale Environment 360. He is deeply alarmed at the prospect for coral reefs and wants to communicate why as clearly and accurately as he can. He begins by acknowledging that warnings of dire threats to coral reefs have been common over past decades; in his 40 years of working on reefs he has often been concerned at the impacts of sediments, nutrients and habitat loss. But the devastation which global warming threatens is of a different order.
Veron is frank about the depth of his anxiety. He writes of the ’long period of deep personal anguish’ he felt when he realised the big picture that was emerging from his widespread research into the effect of global temperature changes on reefs. He speaks of turning in his dismay to specialists in many different fields of science to find ’anything that might suggest a fault’ in his conclusions. But without success. The bottom line remains that coral reefs can be utterly trashed in the lifetime of today’s children.
He realises that such a conclusion will be treated as an exaggeration by many. People may think that while there may be something to worry about it won’t be as bad as doomsayers like him are predicting.
’This view is understandable given that only a few decades ago I, myself, would have thought it ridiculous to imagine that reefs might have a limited lifespan on Earth as a consequence of human actions. It would have seemed preposterous that, for example, the Great Barrier Reef – the biggest structure ever made by life on Earth – could be mortally threatened by any present or foreseeable environmental change.
’Yet here I am today, humbled to have spent the most productive scientific years of my life around the rich wonders of the underwater world, and utterly convinced that they will not be there for our children’s children to enjoy unless we drastically change our priorities and the way we live.’
He goes on to explain the issues with helpful clarity. Single-celled algae live in coral cells and provide the photosynthetic fuel for them to grow and reefs to form. High light conditions at the same time as above-normal water temperatures cause the algae to produce toxic levels of oxygen.
’Under these conditions, corals must expel the zooxanthellae, bleach, and probably die or succumb to the toxin and definitely die. A tough choice, one they have not had to make at any time in their long genetic history.’
They can recover from bleaching, but not if further events continue to occur while the ecosystem is re-establishing. Increasing ocean heat, which affects surface layers most, will mean increasing severity and frequency of bleaching events.
’Scientists don’t need a pocket calculator to conclude that compressing the time periods between events in this way will prevent recovery: If we do not take action, the only corals not affected by mass bleaching by 2050 will be those hiding in refuges away from strong sunlight.’
However, serious though bleaching is, the effects of ocean acidification will be much more serious, affecting coral reefs badly and also impacting on all marine ecosystems. He considers that ocean acidification has played a major part in each of the five major extinctions in Earth’s history. In the last four extinctions reefs disappeared for millions of years. Reversal of acidification is a long process which can take place only through the immensely slow weathering and dissolution processes of geological time, processes that take hundreds of thousands to millions of years.
Veron asks his readers to consider two facts:
’The atmospheric levels of CO2 we are already committed to reach, no matter what mitigation is now implemented, have no equal over the entire longevity of the Great Barrier Reef, perhaps 25 million years. And most significantly, the rate of CO2 increase we are now experiencing has no precedent in all known geological history.’
He concludes with a solemn reminder:
’Reefs are the ocean’s canaries and we must hear their call. This call is not just for themselves, for the other great ecosystems of the ocean stand behind reefs like a row of dominoes. If coral reefs fail, the rest will follow in rapid succession, and the Sixth Mass Extinction will be upon us – and will be of our making.’
I realise it’s only a week since I last wrote on the effect of global warming on corals. Veron is not saying anything that others aren’t also pointing to, or that he hasn’t himself said before. But he’s saying it with great lucidity and there’s an urgency and poignancy to the article which impressed me and made me want to draw attention to it. Scientific reticence is not permitted to mute the expression of his profound concern. The issue is too fundamental for that.
’We cannot afford to wait until the predictions of science can be totally verified, because by that time it will be too late.’