Impact on the Marine Environment

Rises in sea-level were predicted by the IPCC as happening ‘over a period of time ranging from centuries to millennia’. Partial melting of the Greenland ice sheet, and possibly the West Antarctic ice sheet, it said, would cause a sea-level rise of 4 to 6 metres; complete melting over Greenland would add another metre to the level of the Atlantic. Since its report in 2007, and with unexpectedly rapid loss of Greenland ice, the IPCC’s estimates of the rate of sea-level rise have seemed conservative to many climate scientists.

Surface warming of the ocean leads to thermal expansion of the water – the biggest factor in sea-level rise. There has been an increase of 0.85oC. in the temperature of the Irish coastal sea since 1950 and 2007 was the warmest year in Irish coastal record. Since the beginning of satellite measurement, sea-levels around Ireland are rising about 3.5 cm per decade, and the present projection by Irish scientists is for a 60cm rise by the century’s end. This alone will magnify the impact of changing storm surges and wave patterns. Some wave heights are reaching an extra 30cm in winter, with more frequent extreme waves in most regions and especially the north-west. The white plumes of spray at distant islands in my window can already be awesome, indeed. As for sea-level rise of more than metre, precipitated by the melting of polar shelves and glaciers – this possibility, agrees the Environment Protection Agency, ‘becomes a cause of concern in its own right’.

One effect of the CO2 burden in the atmosphere, is the progressive, if long-term, acidification of seawater. The oceans remove about a quarter of the CO2 from human activity: indeed, one worry is that the ocean will be less and less able to aborb the gas: cold seawater favours the uptake of CO2 from the atmosphere while warmer ocean temperatures can trigger its release from the sea. Ocean life is used to slightly alkaline water - a pH level around 8 - but the balance towards acidity has been shifting at an unprecedented rate over the past century, with measurable effects even in the deep ocean.

Nephrops Lobster
©Michael Viney

For marine organisms to make their shells, plates and skeletons, seawater has to be supersaturated with calcium and carbonate ions: otherwise, seemingly tough substances will start to dissolve again. Some structures come to mind at once – the fragile globes of sea urchins, say, or the biscuity armour of crabs and lobsters. Most molluscs, too, such as oysters and whelks, are potential victims of acidification. All this has immediate implications for Ireland’s shellfish aquaculture, and for the little lobsters, Nephrops (usually called ‘prawns’) that are such a valuable catch for Ireland’s fishing industry. The wider concern must be for the ocean as a whole, its ecosystems crucially interlaced with calcium, even to deep-sea corals and plankton basic to the food-web of everything from fish to whales.

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