Ocean acidification

Assessment versions

Published (reviewed and quality assured)

• 09 Aug 2021, 01:30 PM
  - Ocean acidification

Rationale

Justification for indicator selection

No rationale has been identified for this indicator

Scientific references

• No rationale references available

Indicator definition

This indicator illustrates the global mean average rate of ocean acidification, quantified by decreases in pH, which is a measure of acidity, defined as the hydrogen ion concentration. A decrease in pH value corresponds to an increase in acidity.

The observed decrease in ocean pH resulting from increasing concentrations of CO₂ is an important indicator of change in the global ocean and the impacts of climate change.

This indicator provides information on:

• trends in ocean acidity measured at the Aloha station;
• yearly mean surface seawater pH levels reported on a global scale is computed from monthly pH values by CMEMS.

Units

Acidity is measured in pH.

Policy context and targets

Context description

Acidification is addressed in the 2030 Agenda for Sustainable Development (UN, 2021). One of the targets under Sustainable Development Goal (SDG) 14 (‘Conserve and sustainably use the oceans, seas and marine resources for sustainable development’), SDG 14.3, is to ‘Minimize and address the impacts of ocean acidification, including through enhanced scientific cooperation at all levels’.

On 4 March 2020, the European Commission proposed a European climate law (EC, 2020) to ensure a climate-neutral European Union by 2050 as a part of the European Green Deal (EC, 2019). This law is designed to establish a basis for adaptable management, with focus on the implementation of mitigation measures, the monitoring of progress and the improvement of management approaches if needed.

Targets

No targets have been specified

Related policy documents

No related policy documents have been specified

Methodology

Methodology for indicator calculation

• The time series are based both on direct pH measurement data from the Hawaii Ocean Time-series, obtained from the Aloha station, and gap-filling calculations using data from this station (Carter et al., 2016, 2018), and on a reconstruction of global yearly mean surface pH values from CMEMS.
• A trend line has been added for the CMEMS data.
• The Aloha time series data are based onin situmeasurements and calculation of pH values based on dissolved inorganic carbon concentrations and total alkalinity (Dore et al., 2009; Dore, 2012).
• A time series of annual global mean surface seawater pH for the period 2001-2016, based on the CMEMS three-step methodology (Copernicus Marine Service, 2021), has been used for the indicator for the first time. The aim of future CMEMS work is to deliver pan-EU and regional assessments of acidification. This indicator will also be used for reporting under SDG 14. Global average surface ocean pH values derived from CMEMS data are based on a reconstruction method usingin situand remote-sensing data, as well as empirical relationships. The indicator is available at annual resolution, and from the year 2001 onwards. The error for each yearly pH value is 0.003.
• The estimated global mean surface seawater pH is based on alkalinity values (obtained using the locally interpolated alkalinity regression (LIAR) method after Carter et al. (2016, 2018)), surface ocean partial pressure of CO₂ (pCO₂) (CMEMS product) and an evaluation of a gridded field of ocean surface pH values based on CO₂ system calculations (van Heuven et al., 2011), see (Copernicus Marine Service, 2021).

References

Archer, D. and Brovkin, V., 2008, ‘The millennial atmospheric lifetime of anthropogenic CO₂’,Climatic Change90(3), pp. 283-297 (DOI: 10.1007/s10584-008-9413-1).

Bindoff, N. L., et al., 2019, ‘Changing ocean, marine ecosystems, and dependent communities’, in: Pörtner, H.-O. et al. (eds),IPCC special report on the ocean and cryosphere in a changing climate, Cambridge University Press, Cambridge, UK.

Carter, B. R., et al., 2016, ‘Locally interpolated alkalinity regression for global alkalinity estimation’,Limnology and Oceanography: Methods14(4), pp. 268-277.

Carter, B. R., et al., 2018, ‘Updated methods for global locally interpolated estimation of alkalinity, pH, and nitrate’,Limnology and Oceanography: Methods16(2), pp. 119-131.

Copernicus Marine Service, 2020a,Product user manual: For global ocean surface carbon product MULTIOBS_GLO_BIO_CARBON_SURFACE_REP_015_008(https://resources.marine.copernicus.eu/documents/PUM/CMEMS-MOB-PUM-015-008.pdf) accessed 1 April 2021.

Copernicus Marine Service, 2020b,Quality information document: Global ocean surface carbon product MULTIOBS_GLO_BIO_CARBON_SURFACE_REP_015_008(https://resources.marine.copernicus.eu/documents/QUID/CMEMS-MOB-QUID-015-008.pdf) accessed 1 April 2021.

Copernicus Marine Service, 2021, ‘Global mean sea water pH’, Copernicus Marine Service (https://marine.copernicus.eu/access-data/ocean-monitoring-indicators/global-mean-sea-water-ph) accessed 1 April 2021.

Dore, J. E., et al., 2009, ‘Physical and biogeochemical modulation of ocean acidification in the central North Pacific’,Proceedings of the National Academy of Sciences of the United States of America106, pp. 12235-12240 (DOI: 10.1073/pnas.0906044106).

Dore, J. E., 2012, ‘Hawaii Ocean Time-series surface CO₂ system data product, 1988-2008.’, SOEST, University of Hawaii, Honolulu, HI. (http://hahana.soest.hawaii.edu/hot/products/products.html).

EC, 2019, Communication from the Commission to the European Parliament, the European Council, the Council, the European Economic and Social Committee and the Committee of the Regions ‘The European Green Deal’ (COM(2019) 640 final of 11 December 2019).

EC, 2020, Proposal for a regulation of the European Parliament and of the Council establishing the framework for achieving climate neutrality and amending Regulation (EU) 2018/1999 (European Climate Law) (COM(2020) 80 final).

Helcom, 2013,Climate change in the Baltic Sea Area — Helcom thematic assessment in 2013, Baltic Sea Environment Proceedings No 137, Helsinki Commission — Baltic Marine Environment Protection Commission, Helsinki (http://www.helcom.fi/Lists/Publications/BSEP137.pdf) accessed 27 October 2013.

Joos, F., et al., 2011, ‘Impact of climate change mitigation on ocean acidification projections’, in:Ocean acidification, Oxford University Press, Oxford, pp. 272-288.

Kahn, B., 2016, ‘Earth’s CO₂ passes the 400 PPM threshold — maybe permanently’,Scientific American, 27 September 2016 (https://www.scientificamerican.com/article/earth-s-co2-passes-the-400-ppm-threshold-maybe-permanently/) accessed 19 April 2021.

Orr, J. C., et al., 2005, ‘Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms’,Nature437(7059), pp. 681-686 (DOI: 10.1038/nature04095).

Rhein, M., et al., 2013, ‘Observations: ocean’, in: Stocker, T. F. et al. (eds),Climate change 2013: The physical science basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK; New York, NY, pp. 255-316.

School of Ocean and Earth Science and Technology, 2021, ‘Hawaii Ocean Time-series (HOT)’, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa (https://hahana.soest.hawaii.edu/hot/products/products.html) accessed 1 April 2021.

UN, 2015, ‘Transforming our world: the 2030 Agenda for Sustainable Development’, United Nations (https://sustainabledevelopment.un.org/post2015/transformingourworld) accessed 1 April 2021.

UN, 2021, ‘The Sustainable Development Agenda’, Sustainable Development Goals, United Nations (https://www.un.org/sustainabledevelopment/development-agenda/) accessed 1 April 2021.

van Heuven, S., et al., 2011,CO2SYS v 1.1: MATLAB program developed for CO2 system calculations. ORNL/CDIAC-105b, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, US Department of Energy, Oak Ridge, TN.

Methodology for gap filling

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

Methodology references

• See references under Methodology - References

Data specifications

EEA data references

• No datasets have been specified here.

External data references

• GLOBAL MEAN SEA WATER PH
• Hawaii Ocean Time-series (HOT)

Data sources in latest figures

Uncertainties

Methodology uncertainty

No uncertainty has been specified

Data sets uncertainty

No uncertainty has been specified

Rationale uncertainty

No uncertainty has been specified