Cutting carbon emissions vital to stemming ocean acidity, say scientists

Posted: 13 July 2005

Rising levels of carbon dioxide in the atmosphere, from the burning of fossil fuels, has already increased the acidity of the world's oceans to a level that is irreversible in our life times, warns a new report published by the Royal Society, the UK's national academy of science.

The oceans act as a sponge, taking up carbon dioxide from the atmosphere which dissolves and forms an acid in the seawater.

Gorgonian soft coral on sea fan, Red Sea.
Gorgonian soft coral on sea fan, Red Sea.
Gorgonian soft coral on sea fan, Red Sea. Corals are under threat by global warming on two fronts: from bleaching due to warmer sea temperatures and increased acidity of the oceans resulting from rising carbon dioxide levels in the atmosphere.Photo: Mary Lou Frost/ICRIN
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." Failure to cut carbon emissions will threaten "many of the species and ecosystems that we know today," he warns.

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.

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.

Species at risk

This will affect 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 some creatures in the Antarctic Ocean like plankton will be among the first to be affected, which 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 like squid to obtain oxygen from seawater, says the report.

"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," said Professor Raven.

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.

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.

The report looks at various ways of tackling rising acidity such as adding limestone to the oceans to make them more alkaline. But, it concludes, the only practical way to stem the rising levels of acidity in our oceans and minimise the risk to marine life is by reducing carbon emissions in the atmosphere.

"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," said Professor Raven.

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