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Cuts in carbon dioxide emissions vital to stem rising acidity of oceans

30 June 2005

Cuts in emissions of the greenhouse gas carbon dioxide are the only way to stem the rising levels of acidity in our oceans and prevent potentially damaging consequences for marine life warns a new report published by the Royal Society today (Thursday 30 June 2005).

According to the report, Ocean acidification due to increasing atmospheric carbon dioxide, excess carbon dioxide in the atmosphere, from man's burning of fossil fuels, has already increased the acidity of the world's oceans to a level that is irreversible in our life times(1). This is because the oceans act as a sponge, taking up carbon dioxide from the atmosphere which dissolves and forms an acid in the seawater.

Professor John Raven, chair of the Royal Society working group on ocean acidification said: "Along with climate change, the rising acidity of our oceans is yet another reason for us to be concerned about the carbon dioxide we are pumping into the atmosphere. Our world leaders meeting at next week's G8 summit must commit to taking decisive and significant action to cut carbon dioxide emissions. Failure to do so may mean that there is no place in the oceans of the future for many of the species and ecosystems that we know today."

Sea creatures such as corals, shell fish, sea urchins and star fish are likely to suffer the most because higher levels of acidity makes it difficult for them to form and maintain their hard calcium carbonate skeletons and shells. For example, even under the 'low' predictions for future carbon dioxide emissions into the atmosphere, the combined effects of climate change and ocean acidification mean that corals could be rare on tropical and subtropical reefs, such as the Great Barrier Reef, by 2050. This will have major ramifications for hundreds of thousands of other species that dwell in the reefs as well as for the people that depend upon them, both for food and to help to protect coastal areas from, for example, tsunamis.

The report says that changes in ocean chemistry, caused by ocean acidification, means that we can predict that some creatures in the Antarctic Ocean will be among the first to be affected. For example, some types of plankton a major source of food for fish and other animals   may be unable to make their calcium carbonate shells by 2100. This may have significant consequences for entire food webs in the region, although the overall impact of this is unclear.

Higher concentrations of carbon dioxide may also make it harder for some larger marine animals to obtain oxygen from seawater. For example, squid are particularly sensitive because they move by jet propulsion   this is very energy-demanding and requires a good supply of oxygen.

Professor Raven said: "Basic chemistry leaves us in little doubt that our burning of fossil fuels is changing the acidity of our oceans. And the rate change we are seeing to the ocean's chemistry is a hundred times faster than has happened for millions of years. We just do not know whether marine life which is already under threat from climate change   can adapt to these changes."

By absorbing carbon dioxide the oceans actually help stave off climate change. In the past 200 years the oceans have absorbed about half of the carbon dioxide produced by humans, primarily through the burning of fossil fuels. They are currently taking up one tonne of this carbon dioxide for each person on the planet every year. 

However, the report warns that rising levels of acidity in the ocean may mean that the ability of the oceans to mop up carbon dioxide from the atmosphere will be reduced. This is because the chemistry of the surface waters of the ocean means that as carbon dioxide is added, its ability to take up more is decreased. Furthermore, any rise in ocean temperatures, due to climate change, could reduce the ability of the surface waters to take up carbon dioxide from the atmosphere.

Professor Raven said: "The oceans play a vital role in the earth's climate and other natural systems which are all interconnected. By blindly meddling with one part of this complex mechanism, we run the risk of unwittingly triggering far reaching effects."

The report looks at various ways of tackling rising acidity such as adding limestone to the oceans to make them more alkaline. However, it found that the only practical way to minimise the risk to the oceans and marine life is to reduce emissions of carbon dioxide into the atmosphere (2).

The report point out that there is still much uncertainty around the impacts of ocean acidification and recommends that a major international effort be launched into this relatively new area of research.

  1. Calculations indicate that the oceans uptake of carbon dioxide has led to a reduction of the pH (the scale of acidity whereby a reduction in pH indicates a rise in acidity) of surface seawater of 0.1 units. If the global emissions of carbon dioxide from human activities continue to rise on current trends then the average pH is projected to fall by up to 0.5 units by 2100. Surface oceans currently have an average pH of 8.2.
  2. The report recommends that if the risk of irreversible damage arising from ocean acidification is to be avoided, particularly in the Southern Ocean, the cumulative future emissions of carbon dioxide from human activities to the atmosphere must be considerably less than 900 Giga tonnes of Carbon by 2100.