If ocean acidification sounds hard to understand, what about “a great big gorilla in the cupboard”? One that cleans out reefs, leaving them “horrible places – dead, empty, slime-covered.”
Those were the words used by Australian scientist and coral reef expert John Veron in a lecture given to the Royal Society in London last month. It’s available online and I have watched it more than once. He paints a grim picture. His seriousness and the weight of his concern are deeply impressive. Veron warned that his talk would not be a happy one. Usually his talks on coral are fun. This one wouldn’t be, but “I’ve never given a more important talk in my life.” It was highly focused and informative, accompanied throughout by a range of illuminating pictures and graphs. I offer a rough synopsis in what follows.
But first a little background to the occasion. The Royal Society is concerned that the coral reef crisis doesn’t receive the attention it warrants as one of the major indications of threatening climate change disaster. It has been attempting to remedy that. In July, in combination with the Zoological Society of London and the International Programme on the State of the Ocean, it facilitated a Coral Reef Crisis meeting to identify key thresholds of atmospheric carbon dioxide needed for coral reefs to remain viable. Veron’s lecture was hosted as part of the event. David Attenborough who introduced Veron described him as one of the great authorities of the world on coral and stressed that his knowledge was first-hand and authoritative.
Veron spoke of the uniqueness of coral reefs, defined by several factors: they live at the interface of atmosphere and ocean, which is physically and chemically stressful; they are geological structures yet they are alive; they are closely attuned to the hostile environment in which they exist, dependent on light as trees are, sensitive to optimum temperature (31 degrees in Great Barrier), and dependent on the carbonate chemistry of the oceans.
Coral reefs are nature’s historians. Whether in fossil form or living their growth layers not only indicate rate of growth but also contain information about the environment in which they grew. Ancient reefs uplifted in land, of which he had some great pictures, preserve this information for us to read.
He went on to talk about the great mass extinction events, in which corals were always deeply affected, in the Permian to the point of total extinction and in others to near extinction. It is the precariousness of their habitat which makes them extremely sensitive to climate change. The mass extinctions are closely related to the carbon cycle, particularly to carbon dioxide and ocean acidification, with methane sometimes playing a part.
He explained the mass bleaching phenomenon. Coral is dependent on the algae which live in its tissues. Overheating – just a little – causes the algae to produce too much oxygen which kills corals. This is something which hasn’t happened for millions of years. It started only in the 1980s. Mass bleaching events can turn coral to rubble, though if the ocean conditions are right it will start to grow again. He looked at carbon dioxide concentrations and what they have meant for the Great Barrier Reef (GBR) as representative of all reefs.
At 320 parts per million there was some mass bleaching, but only in patches. At 350 ppm there was a lot of mass bleaching all over the GBR and many other reefs as well. Today at 387 ppm there is compounding long-term degradation on the GBR. Held at this level indefinitely the GBR would slowly decline. The upper 20 or 30 metres would gradually become more or less rubble. At 400 ppm there will be more severe weather events affecting the reef and severe bleaching will occur, mainly during El Nino cycles. 450 ppm will cause severe bleaching most years, irrespective of the natural cycles. At 500 ppm there won’t be anything left to bleach.
Ocean acidification, is a “very, very serious thing indeed” not only for corals but for anything that forms a carbonate skeleton. We have every reason to worry about it. He showed a picture of what a reef looks like when acidification takes hold. Horrible is certainly the word.
The future is all about synergies, the way various factors combine to produce the effect on coral reefs. In 25 years time the combination of carbon dioxide levels at 450 ppm, plus acidification, plus warmer temperature, means there will be mass bleaching most years, which will mean very extensive habitat destruction and the beginning of extinctions.
In 50 years time at 600 ppm, plus further acidification, plus even warmer temperatures, plus sea level rise of 400 mms, we get the following: no coral will occur shallower than 10 metres, calcification of anything will be marginal, extinctions will be extensive, reefs will be highly erosional, there will be no shallow water habitats, coralline algae which hold the reefs together won’t exist, there will be major impacts from sea-level rise and super-cyclones.
At that point we are heading for a mid-Eocene climate and accompanying extinctions. Certainly our carbon dioxide levels will not be as high as they were then, but we are increasing them so fast that the carbon dioxide is remaining in the surface skin of the oceans; it is not getting injected down into deep water where it can be buffered by the carbonates which will de-acidify water.
In 75 years from now at 800 ppm, plus further acidification effects, plus 5 degrees warming: some corals may survive in askeletal form, but there will be no reefs, molluscs will be in sharp decline and there will be huge biodiversity loss.
100 years ahead it will be runaway climate change which is producing the carbon dioxide. Corals will be extinct or askeletal, all other taxa will be going extinct, reefs will be wave-washed geological structures. The sixth mass extinction, such as we had 65 million years ago will be under way. "How can it not be?" One ecosystem after another will tumble, an extinction not just of corals but led by corals.
“However much we want to talk about the economic problems associated with climate change they pale, they’re trivial compared to the problems created if we start up a runaway carbon dioxide climate change explosion.”
A reminder towards the end: 450 ppm will bring on the demise of the GBR. “Not a skerrick of doubt about it.”
It’s a solemn warning from a scientist who clearly wishes he didn’t have to deliver it but can do no other. It’s not surprising that the document produced by a working group in association with the occasion should be plain spoken in its conclusion:
“Coral reefs speak unambiguously about climate change. Abrupt carbonising of the environment will destroy carbonate-based ecosystems. Changes to water chemistry will flow on to all marine ecosystems as the oceans turn hostile to a high proportion of marine life. This is the path of mass extinctions, the most destructive events in all Earth history.
“The Earth’s atmospheric CO2 level must be returned to < 350ppm to reverse this escalating ecological crisis and to 320ppm to ensure permanent planetary health. Actions to achieve this must be taken urgently. The commonly mooted best case target of 450ppm and a time frame reaching to 2050 will plunge the Earth into an environmental state that has not occurred in millions of years and from which there will be no recovery for coral reefs and for many other natural systems on which humanity depends.”
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