Ocean acidification

Assessment versions

Published (reviewed and quality assured)

• Ocean acidification (CLIM 043) - Assessment published Nov 2012

Justification for indicator selection

Across the ocean, the pH of surface waters has been relatively stable for millions of years. Over the last million years, average surface-water pH oscillated between 8.3 during cold periods (e.g. during the last glacial maximum, 20 000 years ago) and 8.2 during warm periods (e.g. just prior to the industrial revolution). Human activities are threatening this stability by adding large quantities of CO₂ to the atmosphere, which is subsequently partially absorbed in the ocean. This process is referred to as ocean acidification because sea water pH is declining, even though ocean surface waters will remain alkaline.

When CO₂ is absorbed by the ocean, it reacts with water, producing carbonic acid. The role of the carbonate ion is special because it acts as a buffer, helping to limit the decline in ocean pH; however, it is being used up as we add more and more anthropogenic CO₂ to the ocean. As carbonate ion concentrations decline, so does the ocean’s capacity to take up anthropogenic CO₂. Currently, the ocean takes up about one fourth of the global CO₂ emissions from combustion of fossil fuels, cement production and deforestation. Hence, the ocean serves mankind by moderating atmospheric CO₂ and thus climate change, but at a cost, namely changes in its fundamental chemistry.

It has been shown that corals, mussels, oysters and other marine calcifiers have a more difficult time constructing their calcareous shell or skeletal material as the concentration of carbonate ions decreases. Most, but not all, marine calcifying organisms exhibit the same difficulty. Furthermore, pH is a measure which affects not only inorganic chemistry but also many biological molecules and processes, including enzyme activities, calcification and photosynthesis. Thus, anthropogenic reductions in sea water pH could affect entire marine ecosystems. A comprehensive recent study suggests that all coral reefs will cease to grow and start to dissolve at an atmospheric CO₂ level of 560 ppm due to the combined effects of acidification and warming. This CO₂ concentration would be attained by 2050 under high business-as-usual emissions scenarios. Other organisms and ecosystems are likely to have different thresholds.

Scientific references:

• IPCC 2007: Climate Change: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. (S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor and H. L. Miller, eds.). Cambridge University Press, Cambridge.

Indicator definition

• Decline in ocean acidity

Units

• acidity (pH)

Policy context and targets

Context description

Targets

No targets have been specified.

Related policy documents

• Climate-ADAPT: Mainstreaming adaptation in EU sector policies
  Overview of EU sector policies in which mainstreaming of adaptation to climate change is ongoing or explored
• Climate-ADAPT: National adaptation strategies
  Overview of activities of EEA member countries in preparing, developing and implementing adaptation strategies
• DG Climate Action: What is the EU doing about climate change?
  Activities of the EU regarding climate change (both mitigation and adaptation)
• White paper - Adapting to climate change: towards a European framework for action
  EU framework for adaptation to climate change, leading to a comprehensive EU adaptation strategy by 2013

Methodology

Methodology for indicator calculation

The time series shows both direct measurement data from the Aloha station pH as well as calculations for gap filling (see methodology reference below).

A trend line has been added.

Methodology for gap filling

The methodology for gap filling is described in the reference below.

Methodology references

• Dore et al. 2009: Physical and biogeochemical modulation of ocean acidification in the central North Pacific. Dore, J. E., Lukas, R., Sadler, D. W., Church, M. J. and Karl, D. M. (2009)  Proceedings of the National Academy of Sciences 106, 12235–12240. doi:10.1073/pnas.0906044106

Data specifications

EEA data references

• No datasets have been specified here.

External data references

• Station ALOHA Surface Ocean Carbon Dioxide

Data sources in latest figures

Uncertainties

Methodology uncertainty

Not applicable

Data sets uncertainty

In general, changes related to the physical and chemical marine environment are better documented than biological changes because links between cause and effect are better understood and often time series of observations are longer. Ocean acidification occurs as a consequence of well-defined chemical reactions, but its rate and biological consequences on a global scale is subject to research.

Further information on uncertainties is provided in Section 1.7 of the EEA report on Climate change, impacts, and vulnerability in Europe 2012 (http://www.eea.europa.eu/publications/climate-impacts-and-vulnerability-2012/)

Rationale uncertainty

No uncertainty has been specified