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The effects of ocean acidification on corals are particularly concerning since one quarter of all marine species depend on coral reefs for homes, nurseries, feeding grounds and spawning sites

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Ocean acidification: the facts

Ecologist

10th December, 2009

The marine campaign group Oceana has put together a fact sheet about ocean acidification


What is ocean acidification?


Ocean acidification is the process caused by increasing man-made carbon dioxide emissions, by which the oceans are becoming more acidic.

When carbon dioxide enters the ocean, it combines with seawater to produce carbonic acid, which increases the acidity of the water.

Rising carbon dioxide emissions, primarily from the burning of fossil fuels for energy, has led to a 30 per cent rise in ocean acidity from pre-industrial levels, as measured by a fall of 0.1 units in the pH of ocean surface waters.

If carbon emissions growth continues at the current rate, the pH of ocean surface water will fall 0.2 units by 2050, lower than at any time in the last 20 million years. By the end of this century, the pH will have fallen 0.4 units from its natural level – close to a doubling of ocean acidity. The change is happening 100 times faster than at any time in the history of the planet.

How will ocean acidification affect marine life?

Ocean acidification leads to a reduction in the amount of carbonate ions in the water. Many marine animals need carbonate ions for the calcium carbonate required to form skeletons and shells. This will affect their development and ability to reproduce – ultimately threatening their populations.

Species under the most immediate threat include corals, crabs, lobsters, clams and oysters. 

Falling numbers of less well-known species, like pteropods – tiny swimming snails – have significant effects further up the food chain. Pteropods are important sources of nutrition for many types of fish, whales and birds in polar and sub-polar regions.

The effects on corals, already highly sensitive to their environment, are particularly concerning, since one quarter of all marine species depend on coral reefs for homes, nurseries, feeding grounds and spawning sites.

This equates to nine million marine species, including four thousand species of fish. OCEANA forecasts the mass extinction of corals in both tropical and cold waters this century, if carbon emissions growth continues unchecked.
 
How will ocean acidification affect humans?

Further declines in fish and shellfish stocks will impact an important source of protein for millions of people. In 2006, fish provided more than 2.9 billion people with at least 15 percent of their average animal protein intake.
 
The livelihoods of the world's 47.5 million fishermen will also be adversely affected. The fishing industry is estimated to employ a further 120 million people, supporting 8 per cent of the world's population.

What can be done to prevent this?

The cause of ocean acidification is man-made carbon dioxide emissions, produced mainly by the burning of fossil fuels for transport (cars, buses, trains, ships, planes), by some industrial processes, and the production of electricity (coal, oil and gas power plants). 

The level of man-made carbon dioxide emissions is typically given by measuring the concentration of carbon dioxide in the Earth's atmosphere. This is currently 385 parts per million.

The 'tipping point' for coral reefs – when they will die and be unable to
recover - will come when carbon dioxide concentrations reach 450ppm. At current rates of growth, this will happen by middle to end of this century.

To return the oceans to normalcy will require stabilization of carbon dioxide concentrations at 350ppm or less. This means reducing global carbon dioxide emissions by 80-90 per cent by 2050. This can only be achieved by a massive shift away from fossil fuels to alternative sources of energy (wind, solar).

Useful links

Find out more at Oceana

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