Kleypas et al., 2005:

"The oceans cover over two-thirds of the Earth’s surface. They play a vital role in global biogeochemical cycles, contribute enormously to the planet’s biodiversity and provide a livelihood for millions of people.

The oceans are absorbing carbon dioxide (CO₂) from the atmosphere and this is causing chemical changes by making them more acidic (that is, decreasing the pH of the oceans). In the past 200 years the oceans have absorbed approximately half of the CO₂ produced by fossil fuel burning and cement production. Calculations based on measurements of the surface oceans and our knowledge of ocean chemistry indicate that this uptake of CO₂ has led to a reduction of the pH of surface seawater of 0.1 units, equivalent to a 30% increase in the
concentration of hydrogen ions.

If global emissions of CO₂ from human activities continue to rise on current trends then the average pH of the oceans could fall by 0.5 units (equivalent to a three fold increase in the concentration of hydrogen ions) by the year 2100. This pH is probably lower than has been experienced for hundreds of millennia and, critically, this rate of change is probably one hundred times greater than at any time over this period. The scale of the changes may vary regionally, which will affect the magnitude of the biological effects.

Ocean acidification is essentially irreversible during our lifetimes. It will take tens of thousands of years for ocean chemistry to return to a condition similar to that occurring at pre-industrial times (about 200 years ago). Our ability to reduce ocean acidification through artificial methods such as the addition of chemicals is unproven. These techniques will at best be effective only at a very local scale, and could also cause damage to the marine environment. Reducing CO₂ emissions to the atmosphere appears to be the only practical way to
minimise the risk of large-scale and long-term changes to the oceans.

All the evidence collected and modelled to date indicates that acidification of the oceans, and the changes in ocean chemistry that accompany it, are being caused by emissions of CO₂ into the atmosphere from human activities. The magnitude of ocean acidification can be predicted with a high level of confidence. The impacts of ocean acidification on marine organisms and their ecosystems are much less certain but it is likely that, because of their particular physiological attributes, some organisms will be more affected than others.

Predicting the direction and magnitude of changes in a complex and poorly studied system such as the oceans is very difficult. However, there is convincing evidence to suggest that acidification will affect the process of calcification, by which animals such as corals and molluscs make shells and plates from calcium carbonate. The tropical and subtropical corals are expected to be among the worst affected, with implications for the stability and longevity of the reefs that they build and the organisms that depend on them. Cold-water coral reefs
are also likely to be adversely affected, before they have been fully explored.

Other calcifying organisms that may be affected are components of the phytoplankton and the zooplankton, and are a major food source for fish and other animals. Regional variations in pH will mean that by 2100 the process of calcification may have become extremely difficult for these groups of organisms particularly in the Southern Ocean. Some shallow water animals, which play a vital role in releasing nutrients from sediments, also calcify, and may be affected by changes in the chemistry of the oceans. Some studies suggest that growth and reproduction in some calcifying and non-calcifying marine species could be reduced due to the projected changes in ocean chemistry.

From the evidence available it is not certain whether marine species, communities and ecosystems will be able to acclimate or evolve in response to changes in ocean chemistry, or whether ultimately the services that the ocean’s ecosystems provide will be affected. Research into the impacts of high concentrations of CO₂ in the oceans is in its infancy and needs to be developed rapidly. We recommend that a major, internationally coordinated effort be launched to include global monitoring, experimental, mesocosm and field studies. Models that include the effects of pH at the scale of the organism and the ecosystem are also necessary. The impacts of ocean acidification are additional to, and may exacerbate, the effects of climate change. For this reason, the necessary funding should be additional and must not be diverted from research into climate change.

Oceans play a very important role in the global carbon cycle and Earth’s climate system. There are potentially important interactions and feedbacks between changes in the state of the oceans (including their pH) and changes in the global climate and atmospheric chemistry. Changes in the chemistry of the oceans will reduce their ability to absorb additional CO₂ from the atmosphere, which will in turn affect the rate and scale of global warming. The knowledge of these impacts and effects is currently poor and requires urgent consideration. The
understanding of ocean acidification and its impacts needs to be taken into account by the Intergovernmental Panel on Climate Change and kept under review by international scientific bodies such as the Intergovernmental Oceanographic Commission, the Scientific Committee on Oceanic Research and the International Geosphere-Biosphere Programme.

The socio-economic effects of ocean acidification could be substantial. Damage to coral reef ecosystems and the fisheries and recreation industries that depend on them could amount to economic losses of many billions of dollars per year. In the longer term, changes to the stability of coastal reefs may reduce the protection they offer to coasts. There may also be direct and indirect effects on commercially important fish and shellfish species.

Marine ecosystems are likely to become less robust as a result of the changes to the ocean chemistry and these will be more vulnerable to other environmental impacts (such as climate change, water quality, coastal deforestation, fisheries and pollution). The increased fragility and sensitivity of marine ecosystems needs to be taken into consideration during the development of any policies that relate to their conservation, sustainable use and exploitation, or the communities that depend on them.

If the risk of irreversible damage arising from ocean acidification is to be avoided, particularly to the Southern Ocean, the cumulative future human derived emissions of CO₂ to the atmosphere must be considerably less than 900 Gt C (gigatonnes of carbon) by 2100.

In setting targets for reductions in CO₂ emissions, world leaders should take account of the impact of CO₂ on ocean chemistry, as well as on climate change. These targets must be informed by sound science. Ocean acidification is a powerful reason, in addition to that of climate change, for reducing global CO₂ emissions. Action needs to be taken now to reduce
global emissions of CO₂ to the atmosphere to avoid the risk of irreversible damage to the oceans. We recommend that all possible approaches be considered to prevent CO₂ reaching the atmosphere. No option that can make a significant contribution should be dismissed."

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Citation and/or URL

Kleypas, J.A., Feely, R.A., Fabry, V.J., Langdon, C., Sabine, C.L. & Robbins, L.L., 2006, Impacts of ocean acidification on coral reefs and other marine calcifiers: a guide for future research : a report of a workshop held 18-10 April 2005, St. Petersburg, FL. sponsored by NSF, NOAA and the U.S. Geological Survey

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Spatial Coverage

Global review

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Temporal Coverage

 Historical to present

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Update Frequency

Not applicable 

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Other Information

 None