Planetary Boundaries

Explore the concept of planetary boundaries, a scientific framework that identifies the environmental limits within which humanity can safely operate.

Ocean Acidification

The world’s oceans play a critical role in absorbing carbon dioxide. In fact, oceans have absorbed more than a quarter of the CO₂ released into the atmosphere since the Industrial Revolution. But this service comes with a cost: when carbon dioxide dissolves in seawater, it forms carbonic acid, lowering the ocean’s pH. This process is known as ocean acidification.

Even small changes in pH can have major impacts on marine life. Organisms like coral, shellfish, and plankton build their skeletons and shells from calcium carbonate which is a substance that becomes harder to form in more acidic waters. As these species struggle, entire food chains are affected.

The boundary for ocean acidification is based on the saturation state of aragonite, a form of calcium carbonate used by marine organisms. A healthy ocean has an aragonite saturation state of above 3.0. As CO₂ rises, this value drops, and in some parts of the ocean it has already fallen below safe levels.

Ocean acidification is a silent crisis. It doesn’t generate headlines like heatwaves or floods, but it is transforming marine ecosystems in ways that may be irreversible. Coral reefs, which support over a quarter of all marine species, are especially vulnerable. The loss of reef systems would not only destroy habitats but also reduce food sources and coastal protection for millions of people.