Ocean acidification is a global threat to the world’s oceans, estuaries, and waterways. When carbon dioxide (CO2) combines with seawater, it sets off a chemical reaction that makes seawater more acidified. We call this process ocean acidification or OA. The chemical reactions that occur in ocean acidification lower the pH of seawater, increase hydrogen ions, and decrease the availability of carbonate ions, which many species like shellfish, finfish and coral need to grow, reproduce, and thrive.

Like a sponge, our oceans absorb carbon dioxide from the atmosphere. This exchange has helped regulate the planet’s atmospheric carbon dioxide concentrations as humans have increasingly added more CO2 to the atmosphere, but this regulation comes at a cost for the oceans and sea life, particularly shellfish such as commercially valuable oysters and clams. 

Ocean acidification is best known for its osteoporosis-like effects on shellfish, which makes building and maintaining shells difficult for these creatures. Acidification also affects other species vital to the marine ecosystem, including reef-building corals and pteropods (tiny snails eaten by numerous species such as fish and whales). 

Source: NOAA Fisheries, Understanding Ocean Acidification.  https://www.fisheries.noaa.gov/insight/understanding-ocean-acidification

Both climate change and ocean acidification are primarily driven by the release of CO2 into the atmosphere from human activities such as fossil fuel combustion, deforestation, agriculture, and land use practices. Unlike climate change, which refers to changes in Earth’s temperature due to this increased atmospheric CO2, ocean acidification is not directly tied to the warming of the ocean or atmosphere, but rather is a sequence of chemical reactions taking place due to an excess of CO2 in the atmosphere.

Previously, scientists thought that the ocean’s uptake of CO2 might be a positive force against climate change because the oceans absorb about one-third of human-produced atmospheric  CO2. However, the realization that this CO2 increase is harmful to ocean ecosystems has changed our view of the ocean’s role in this process. Ocean acidification is now an additional consequence of extra CO2 in the atmosphere, with both phenomena working at a pace that some ocean organisms may not be able to adapt to.

Source: Scripps Institution of Oceanography, FAQ: Ocean Acidification.  https://scripps.ucsd.edu/research/climate-change-resources/faq-ocean-acidification

Ocean acidification has now crossed a critical threshold for marine life, according to new research highlighted by The Guardian (Sept 2025).

Since the industrial era, ocean acidity has risen by roughly 30–40%, disrupting marine ecosystems that sustain global food webs, fisheries, and coastal economies.

As the ocean loses its capacity to absorb carbon and buffer climate impacts, scientists warn that acidification has breached a key planetary boundary, threatening not just marine biodiversity but also human livelihoods. Acting today allows governments and partners to protect marine biodiversity, sustain food security, and build ocean resilience as part of broader climate adaptation and mitigation strategies.

Ocean acidification has been shown to cause a range of responses at the organism level that can affect biodiversity and ecosystem structure. 

Direct consequences for marine life can propagate through the food web and affect ocean-related services and uses, including food security from fisheries and aquaculture, livelihoods, transportation, coastal protection, tourism, and cultural heritage. 

Decreases in dissolved carbonate ion concentrations have been shown to impact the growth and larval survival of key marine calcifying organisms, including oysters, crabs, mussels and corals. The production and harvest of seafood from marine calcifiers in both wild and aquaculture-based fisheries is expected to decline, with some aquaculture facilities already implementing monitoring and adaptation strategies for ocean acidification. 

The impacts on coral reefs are numerous, including a decrease in the structural complexity and biodiversity of the reefs, critical breeding ground and habitat for many species of fish. 

Effects on growth, reproduction, and predatory avoidance have also been observed for many other marine organisms including fish larvae. 

Source: Global Ocean Acidification Observing Network (GOA-ON), What Is Ocean Acidification?  https://www.goa-on.org/oa/oa.php

A handful of science networks are working to expand global and regional monitoring and measurement of ocean acidification.

The Global Ocean Acidification Observing Network (GOA-ON) is a collaborative international network to detect and understand the drivers of ocean acidification in estuarine-coastal-open ocean environments, the resulting impacts on marine ecosystems, and to make the information available to optimize modelling studies. It is now organized across 11 regional hubs in the Arctic, Caribbean, Gulf of Guinea, Latin America, Mediterranean, North America, Northeast Atlantic, Northern Africa, Pacific Islands & Territories, South Asia and the Southern Ocean, 

These regional networks are fundamental to providing early warning of the impacts of ocean acidification on natural ecosystems, wild and aquaculture fisheries, coastal protection, tourism and local economies.

The International Atomic Energy Agency’s Ocean Acidification International Coordination Centre (OA-ICC) is another hub for research, capacity building and communication. 

Launched in 2013, the OA-ICC supports Member States in studying and taking action on ocean acidification. Countries are empowered to monitor OA along their coasts, assess impacts on key socio-economic species, explore solutions with local stakeholders, and report data towards SDG 14.3. 

The OA-ICC is hosted by the IAEA’s Marine Environment Laboratories in Monaco, which has pioneered methods to study ocean acidification and associated stressors using nuclear and isotopic techniques. 

In addition to these efforts, regional programmes dedicated to OA monitoring and research have taken place under the Western Indian Ocean Marine Science Association (WIOMSA), the Pacific Community (SPC) and at the Institute for Marine and Coastal Research (INVEMAR) in Colombia.  

Governments are increasingly recognizing ocean acidification (OA) as a critical climate-ocean threat that must be embedded across mitigation and adaptation planning. By integrating ocean acidification actions across mainstream policy agendas, we help governments: take inventory; outline needs and make recommendations; align decisions and investments in the face of climate-ocean change. 

The National OA Action Planning Leadership Circle was launched in 2024 and supports invited Ministries, departments and policy officers across 15 countries in the development and implementation of unique commitments to domestic ocean acidification activities.

Leadership Circle government members are working to incorporate ocean acidification science, mitigation and adaptation aspects across mainstream policy documents including:

1. Nationally Determined Contributions and National Adaptation Plans

2. Sustainable Ocean Plans

3. Marine Strategy Framework Directive (for EU member states)

Through the development of Ocean Acidification Action Plans, OA Alliance members are proactively responding to the impacts of ocean acidification and promoting solutions that advance knowledge into policy action. Find the latest here.

We provide a range of ready-to-use visuals, infographics, and interactive tools to help bring ocean acidification stories to life. For example, our OA StoryMaps combine data, visuals, and narratives from around the world, while our Communications Pack offers downloadable graphics, videos, and messaging guidance for media use.

Find answers to more commonly asked questions in support of your next story here: OA Alliance Media FAQs.