Ocean acidification hazard

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Responsible:Niccolò Calandri

Ocean Acidification Risk assesses hazard from decreasing marine water pH, process mainly caused by carbon dioxide (CO₂) absorption from atmosphere. Lower pH indicates higher acidity, which can have devastating effects on marine life, particularly organisms with calcium carbonate shells or skeletons like corals, mollusks and some plankton types.

To calculate this risk, single variable is used:

Acidity of seawater: annual average sea surface pH, standard measure of acidity [Copernicus Climate Data Store (CDS)].

To calculate risk, we compare predicted annual average pH for analyzed year with reference pH value, calculated as average over historical period 1950-1970. Key indicator is pH drop (pH_drop): pH_drop = pH_historical - pH_year

The methodology described for assessing Ocean Acidification Risk aligns with conclusions of major international scientific bodies.

Special Report on the Ocean and Cryosphere in a Changing Climate
Climate Change 2021: The Physical Science Basis These reports state that oceans are absorbing anthropogenic CO2, causing global-scale pH decrease (acidification).

pH_drop thresholds correspond to physiological and ecological tipping points:

Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios
pH_drop ≈ 0.1 (Risk B/C): Impacts shift from 'undetectable' to 'moderate' for sensitive organisms like warm-water corals and bivalves.
pH_drop ≈ 0.2 (Risk C/D): Many organisms enter 'high risk' zone. Calcification significantly compromised.
pH_drop ≥ 0.3-0.4 (Risk E/F): Nearly all calcifying organism groups classified at 'very high risk'.
Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms With pH_drop > 0.3-0.4, surface waters become undersaturated with aragonite. Organisms like pteropods shells literally begin to dissolve.

In conclusion, our methodology uses metric (pH_drop) recommended by scientific community and its risk thresholds are fully coherent with biological and ecological critical points identified by experimental research and synthesized in major world scientific reports like those of IPCC.

Data Sources & References

Sources

WRD_CDSCA_99

Methodology

The methodology described for assessing Ocean Acidification Risk aligns with conclusions of major international scientific bodies.

The approach is robust because it uses metric recommended by scientific community — pH variation (pH_drop) relative to preindustrial or historical period — and defines risk levels based on documented biological impact thresholds. • Special Report on the Ocean and Cryosphere in a Changing Climate • Climate Change 2021: The Physical Science Basis These reports state that oceans are absorbing anthropogenic CO2, causing global-scale pH decrease (acidification).

pH_drop thresholds correspond to physiological and ecological tipping points: • Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios

pH_drop ≈ 0.1 (Risk B/C): Impacts shift from 'undetectable' to 'moderate' for sensitive organisms like warm-water corals and bivalves.
pH_drop ≈ 0.2 (Risk C/D): Many organisms enter 'high risk' zone. Calcification significantly compromised.
pH_drop ≥ 0.3-0.4 (Risk E/F): Nearly all calcifying organism groups classified at 'very high risk'. • Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms With pH_drop > 0.3-0.4, surface waters become undersaturated with aragonite. Organisms like pteropods shells literally begin to dissolve.