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.
- 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, 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 on in situ measurements and calculation of pH values based on dissolved inorganic carbon concentrations and total alkalinity.
- A time series of annual global mean surface seawater pH for the period 2001-2016, based on the CMEMS three-step methodology, 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 using in situ and 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.), 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 (see Copernicus Marine Service, 2021).
Acidification is addressed in the 2030 Agenda for Sustainable Development. 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 to ensure a climate-neutral European Union by 2050 as a part of the European Green Deal. 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.
No methodology uncertainty has been specified.
No data set uncertainty has been specified.
No rationale uncertainty has been specified.