Ocean Acidification

Planetary Boundary 6

Boundary Status

Status: Within boundary (but approaching threshold)
Control Variable: Aragonite saturation state (Ωarag)

• Current: Ωarag ≈ 2.8 (global mean)
• Boundary: Ωarag ≥ 2.75

Scientific Basis: Ocean absorbs ~25% of anthropogenic CO₂ emissions, forming carbonic acid and lowering pH. Ocean pH has decreased 0.1 units since pre-industrial times (30% increase in acidity). Continued acidification threatens marine ecosystems, particularly calcifying organisms (corals, shellfish, plankton).

Business Relevance

Directly Impacted Sectors

• Fisheries: Shellfish collapse, food web disruption
• Aquaculture: Oyster, mussel, and clam farming
• Tourism: Coral reef degradation
• Coastal Communities: Loss of natural coastal protection
• Pharmaceuticals: Marine-derived compounds

Economic Impacts

• US Pacific Northwest: Oyster larvae die-offs linked to acidification (2007-2009 crisis)
• Global Fisheries: $100B+ industry dependent on marine ecosystems
• Coral Reefs: $375B annual economic value (tourism, fisheries, coastal protection)

Key Standards & Frameworks

Disclosure Standards

• TNFD — Ocean dependencies in LEAP assessment
• EU ESRS E3 — Water and marine resources
• GRI 304 — Biodiversity (marine ecosystems)

Scientific Monitoring

• Global Ocean Acidification Observing Network (GOA-ON) — pH monitoring
• Ocean Acidification Information Exchange (OA-IE) — Data portal

Primary Source Documents

Scientific Foundation

• IPCC Special Report on Ocean and Cryosphere (SROCC) — Ocean acidification projections
• NOAA Ocean Acidification Program — US monitoring and research
• Doney et al. (2009) - Ocean Acidification: The Other CO₂ Problem — Foundational review

Policy Frameworks

• UN Decade of Ocean Science (2021-2030) — Global ocean sustainability
• UN SDG 14 — Life below water
• CBD Aichi Target 10 — Minimize pressures on coral reefs

Recommended Metrics

Emissions-based

• CO₂ Emissions: Total Scope 1, 2, 3 emissions (driver of acidification)
• Emissions Reduction Targets: SBTi-validated 1.5°C pathway

Ocean Dependency

• Revenue from Marine Resources: % dependent on ocean health
• Supply Chain Ocean Dependency: Seafood sourcing, seaweed, marine ingredients

Impact Mitigation

• Blue Carbon Projects: Mangrove/seagrass restoration
• Marine Protected Areas (MPAs): Support or investment in MPAs
• Sustainable Seafood: % certified (MSC, ASC)

Root Cause

Ocean acidification is directly caused by CO₂ emissions. Unlike other planetary boundaries, there is no separate "ocean acidification footprint"—it is a climate change impact. Mitigation requires:

1. Decarbonization: Reduce CO₂ emissions (SBTi targets)
2. Blue Carbon: Restore coastal ecosystems (mangroves, seagrass, salt marshes)
3. Ecosystem Resilience: Reduce other stressors (overfishing, pollution)

Books

Technical Guidance

Carbon Accounting in Practice
CO₂ emissions are the driver of ocean acidification. This book covers:

• GHG accounting across Scope 1, 2, 3
• Emissions reduction planning

Download PDF | View on Amazon

Biodiversity and Ecology Service Accounting
Marine ecosystem service valuation, including coral reefs and fisheries.

Download PDF | View on Amazon

Reporting Frameworks

TNFD Made Simple
Ocean dependencies in nature-related financial disclosures.

Download PDF | View on Amazon

Related Pages

• Climate Change — Root cause (CO₂ emissions)
• Biodiversity Loss — Marine biodiversity impacts
• Freshwater Use — Freshwater-ocean nutrient flows
• Biogeochemical Flows — Coastal eutrophication

Planetary Boundary Status: Stockholm Resilience Centre (2023) | Scientific Basis: IPCC SROCC | Last updated: February 2026