The ocean acidification risk assesses the danger linked to the decrease in seawater pH, caused by the absorption of CO₂, with effects above all on organisms with a calcium carbonate shell or skeleton (corals, molluscs, plankton). It is measured as the expected drop in pH relative to the mean pH of a historical reference period: the greater the drop, the higher the risk. It is computed at the marine grid point closest to the site, only for coastal sites, within 30 km of the coast and below 20 m of elevation: for an inland, non-coastal site the risk does not apply.
Indicator. pH drop (pH_drop), dimensionless. Computed only for coastal sites, within 30 km of the coast and below 20 m of elevation, at the nearest marine grid point; for an inland, non-coastal site the risk does not apply and is shown as N/A.
Data. Monthly mean of the pH (negative logarithm of the hydrogen ion concentration) of the sea surface, from the Copernicus Climate Data Store (CDS). Historical baseline: mean pH over the period 1950–1970. Future projections: 2015–2100, annual mean. Scenarios: SSP1-2.6 / SSP2-4.5 / SSP3-7.0 / SSP5-8.5.
Calculation.
(1) The baseline pH is computed as the mean of the annual mean values over the period 1950–1970.
(2) For each future year and scenario the projected annual mean pH is retrieved.
(3) pH_drop = historical_pH − year_pH is computed.
(4) Thresholds on the pH_drop are applied to assign the level 0–5.
Thresholds → level A–F.
• F: ≥ 0.40
• E: ≥ 0.30
• D: ≥ 0.20
• C: ≥ 0.10
• B: ≥ 0.05
• A: < 0.05.
The pH drop thresholds 0.05 / 0.1 / 0.2 / 0.3 / 0.4 are a xNatura choice without a published source.
From physical to impact. The physical level (A–F) is combined with the production process's sensitivity through the risk matrix (6 physical levels by 5 sensitivity bands) → impact level; the damage curve converts the level into a damage factor, from which the Version 2025 value at risk is derived. The damage factor per class is an xNatura estimate without a published source: the value is indicative.
Sources.
• [Copernicus Climate Data Store (CDS)](Copernicus Climate Data Store (CDS))
• [Special Report on the Ocean and Cryosphere in a Changing Climate](Special Report on the Ocean and Cryosphere in a Changing Climate)
• [Climate Change 2021: The Physical Science Basis](Climate Change 2021: The Physical Science Basis)
• [Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios](Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios)
• [Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms](Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms).
Indicator. pH drop (pH_drop), dimensionless. Computed only for coastal sites, within 30 km of the coast and below 20 m of elevation, at the nearest marine grid point; for an inland, non-coastal site the risk does not apply and is shown as N/A.
Data. Monthly mean of the pH (negative logarithm of the hydrogen ion concentration) of the sea surface, from the Copernicus Climate Data Store (CDS). Historical baseline: mean pH over the period 1950–1970. Future projections: 2015–2100, annual mean. Scenarios: SSP1-2.6 / SSP2-4.5 / SSP3-7.0 / SSP5-8.5.
Calculation.
(1) The baseline pH is computed as the mean of the annual mean values over the period 1950–1970.
(2) For each future year and scenario the projected annual mean pH is retrieved.
(3) pH_drop = historical_pH − year_pH is computed.
(4) Thresholds on the pH_drop are applied to assign the level 0–5.
Thresholds → level A–F.
• F: ≥ 0.40
• E: ≥ 0.30
• D: ≥ 0.20
• C: ≥ 0.10
• B: ≥ 0.05
• A: < 0.05.
The pH drop thresholds 0.05 / 0.1 / 0.2 / 0.3 / 0.4 are a xNatura choice without a published source.
From physical to impact. The physical level (A–F) is combined with the production process's sensitivity through the risk matrix (6 physical levels by 5 sensitivity bands) → impact level; the damage curve converts the level into a damage factor, from which the Version 2025 value at risk is derived. The damage factor per class is an xNatura estimate without a published source: the value is indicative.
Sources.
• [Copernicus Climate Data Store (CDS)](Copernicus Climate Data Store (CDS))
• [Special Report on the Ocean and Cryosphere in a Changing Climate](Special Report on the Ocean and Cryosphere in a Changing Climate)
• [Climate Change 2021: The Physical Science Basis](Climate Change 2021: The Physical Science Basis)
• [Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios](Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios)
• [Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms](Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms).