Climate change

December 11, 2008

Squeezing the marine nutcracker

Filed under: Climate Change, Marine Environments, Water Resources — Barry Brook @ 7:10 pm

I haven’t talked a lot about marine impacts of climate change on this website — mostly because it is quite thoroughly covered by Prof Ove Hoegh-Guldberg in his Climate Shifts blog and Dr Simon Donner on Maribo. But in short, the marine environment is under severe stress from chronic human impacts (over-fishing, dredging, pollution [e.g., chemical and oil spills], structural damage [e.g., dynamite fishing on coral reefs], traffic [boat strikes]. etc.) and a double-whammy from climate change. Assoc. Prof. Corey Bradshaw talked about this in detail here (slides and audio available).

A recent editoral in the peer-reviewed journal Marine Pollution Bulletin, by Prof Charles Sheppard of the University of Warwick, UK, spells out just how grim this ‘marine nutcracker’ is. Why does he use the nutcracker analogy? Because: “…coral reef calcification is squeezed, by temperature near the equator and by acidification from the poles“. Let me explain further, by some selected citation from the essay.

It is not farfetched to say that in the marine environment, coral reefs will be the first major ecosystem to be functionally extinguished because of climate change. Of course, many entire small areas of global systems have disappeared already for a number of reasons, from industrial pollution or coastal construction, and many areas of soft substrate have been totally obliterated (trawled for example). But a whole ecosystem with a pan-tropical span? Probably not

Warming which causes, firstly, widespread bleaching of corals and which is then sufficiently severe and persistent to cause subsequent widespread mortality was not really noticed until the 1970s. It began to be increasingly noticed from the 1980s, and now occurs with frequent if erratic occurrence. The years 1998, 2001/2 and 2005 were seminal. Several predictions (calculations are a better word) have been made that severity and frequency of such events will increase so that the sea temperatures which cause widespread mortality will become a near annual occurrence well within the lifetime of most people alive today. Some suggestions are that, on average – there are many local variations – this will be most severe across a tropical belt and will expand outwards. Some extrapolations (Sheppard 2003) showed that the timing of critical dates are nearest close to the equator, becoming later as one moves polewards, in some oceans at least

But most importantly perhaps, the argument that corals can perhaps move polewards a bit overlooks ocean acidification. The oceans are having to absorb more CO2 than ever before and, to date, half to two thirds of all CO2 generated since the start of the industrial revolution has been absorbed by the surface layers of the sea. It is, in fact, only the smaller portion which has not been absorbed by the ocean which causes our greenhouse effect and which is giving rise to all those conferences about global climate change and warming. That portion which has been absorbed, however, has changed the pH of the surface ocean by 0.1, which is a 30% increase in H+ ions [Ed: Hydrogen] (Royal Society, 2005). As a result, the complexities of the carbonic acid – bicarbonate – carbonate buffering system mean that calcification by marine life is increasingly curtailed

In simple terms, marine systems, especially sensitive areas like tropical coral reefs, are being regularly ’shocked’ by extreme heat wave events, which causes loss of symbiotic algae (microscopic plants that live in the tissues of the coral polyp and provide a source of nutrition) and eventually coral death (and the loss of other shell-forming organisms). Further, as the oceans absorb vast amounts of CO2, the surface waters acidify, which undermines the ability of reef-building organisms to produce skeletons of crystalline calcium carbonate (calcite and aragonite).

To risk adding despair to the despondency, the time lags in the system mean that even if the problem of produced CO2 was solved immediately, and the atmospheric level started to drop today, impacts from acidification will continue for a few decades to come. What we have done already and what we do in the next, say, 20 years, will have an inevitability about it which, as far as we know, will be irreversible in human terms at least

It appears to be part of the natural human scientific mind to prioritise problems. Hence there have been arguments about which is the worst problem of the two described above, or even which is the one to worry about most. This is a false debate. Recovery from a thermal shock of a particular magnitude may be possible in an aragonite saturation state of >4, but would it be possible in a saturation state which has fallen to, say, nearer 3?…

it now seems likely that although temperature rise causes the present noticeable declines in many areas, the pH problem will inexorably assume the ascendancy in becoming the greatest inhibitor to marine life in the oceans as a whole, and that this will be increasingly noticed during the lives of most of us here today

So just as with the ecological impacts of global change in land-based environments, the synergistic interactions of threatening processes are the overarching problem — a common systems feature of the Sustainability Crisis. With further impacts on the base of the marine food web — plankton — the whole biotic ediface begins to crumble. The worst-case-scenarios, at 5 to 6 C warming above pre-industrial levels, is described by Mark Lynas (based on a review of the peer-reviewed literature):

At sea there are only losers. Warm water is a killer. Less oxygen can dissolve, so conditions become stagnant and anoxic. Oxygen-breathing water-dwellers – all the higher forms of life from plankton to sharks – face suffocation… Then would come poisonous hydrogen sulphide from the stagnant oceans. It would be a silent killer: imagine the scene at Bhopal following the Union Carbide gas release in 1984, replayed first at coastal settlements, then continental interiors across the world. At the same time, as the ozone layer came under assault [from the hydrogen sulphide], we would feel the sun’s rays burning into our skin, and the first cell mutations would be triggering outbreaks of cancer among anyone who survived. Dante’s hell was a place of judgment, where humanity was for ever punished for its sins. With all the remaining forests burning, and the corpses of people, livestock and wildlife piling up in every continent, the six-degree world would be a harsh penalty indeed for the mundane crime of burning fossil energy.

Such a vision of the brave new climate is not close to the realm of ‘adaptation’ and cost-benefit analyses set against such scenarios are a mere farce. Yet that is the very future that we — the global human collective — are rapidly pushing the Earth system towards. Closer and closer, year by year, as incrementalism rules the day.


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