The global atmospheric concentration of CO₂ has increased from a pre-industrial value of 280 ppm to 384 ppm, leading to a 30% increase in the acidity of the oceans. This significant increase is 100 times faster than any change in acidity experienced in the marine environment for the last 20 million years and represents a rare geological event in the Earth’s history.

Atmospheric CO2 concentrations are predicted to increase throughout the 21^st century and could exceed 800 ppm by 2100 if anthropogenic emissions continue along current trends. Ocean acidification is a direct consequence of increasing atmospheric CO2 concentrations that is occurring independently of climate change. It can be predicted with a high level of certainty based on the complex but predictable marine carbonate chemistry reactions and cycles of CO₂ as it dissolves in seawater. Ocean acidification will follow the accelerating trend in world CO2 emissions, leading to a 150–185% increase in acidity by 2100, under current emission rates (a decrease of 0.4–0.45 pH units).

...Increasing ocean acidification reduces the availability of carbonate minerals in seawater, important building blocks for marine plants and animals. Carbonate ion concentrations are now lower than at any other time during the last 800,000 years. Furthermore, given current emission rates, it is predicted that the surface waters of the highly productive Arctic Ocean will become under-saturated with respect to essential carbonate minerals by the year 2032, and the Southern Ocean by 2050 with disruptions to large components of the marine food web. Seasonal fluctuations in carbonate mineral saturation in the Southern Ocean could mean that detrimental conditions for the continuing function of marine ecosystems, especially calcifying organisms, develop on much shorter timeframes.

—Scientific Synthesis of the Impacts of Ocean Acidification

According to the study, seas and oceans absorb approximately one quarter of the carbon dioxide emitted to the atmosphere from the burning of fossil fuels, deforestation, and other human activities. As more and more carbon dioxide has been emitted into the atmosphere, the oceans have absorbed greater amounts at increasingly rapid rates. Without this level of absorption by the oceans, atmospheric CO₂ levels would be significantly higher than at present and the effects of global climate change would be more marked. However, the absorption of atmospheric CO₂ results in changes to the chemical balance of the oceans, causing them to become more acidic.

Ocean acidification is irreversible on timescales of at least tens of thousands of years, and substantial damage to ocean ecosystems can only be avoided by urgent and rapid reductions in global emissions of CO₂. Attention must be given for integration of this critical issue at the global climate change debate in Copenhagen.

This CBD study provides a valuable synthesis of scientific information on the impacts of ocean acidification, based on the analysis of more than 300 scientific literatures, and it describes an alarming picture of possible ecological scenarios and adverse impacts of ocean acidification on marine biodiversity.

—Ahmed Djoghlaf, Executive Secretary of the Convention

Among other findings, the study shows that increasing ocean acidification will mean that by 2100 some 70% of cold water corals, a key refuge and feeding ground for commercial fish species, will be exposed to corrosive waters.

In addition, given the current emission rates, it is predicted that the surface water of the highly productive Arctic Ocean will become under-saturated with respect to essential carbonate minerals by the year 2032, and the Southern Ocean by 2050 with disruptions to large components of the marine food source, in particular those calcifying species, such as foraminifera, pteropods, coccolithophores, mussels, oysters, shrimps, crabs and lobsters, which rely on calcium to grow and mature.

An emerging body of research suggests that many of the effects of ocean acidification on marine organisms and ecosystems will be variable and complex and will affect different species in different ways. Evidence from naturally acidified locations confirms, however, that although some species may benefit, biological communities under acidified seawater conditions are less diverse and calcifying (calcium-reliant) species absent.

Many questions remain regarding the biological and biogeochemical consequences of ocean acidification for marine biodiversity and ecosystems, and the impacts of these changes on oceanic ecosystems and the services they provide, for example, in fisheries, coastal protection, tourism, carbon sequestration and climate regulation.

Launched at the Earth Summit in Rio de Janeiro in 1992, the Convention on Biological Diversity is an international treaty for the conservation and sustainable use of biodiversity and the equitable sharing of the benefits from the utilization of genetic resources. The headquarters of the Secretariat of the Convention is located in Montreal.

Resources

• Scientific Synthesis of the Impacts of Ocean Acidification on Marine Biodiversity (CBD Technical Series No. 46)