3.5 Acidification

When a gas like carbon dioxide builds up in the atmosphere, the oceans will absorb much of the surplus gas. The extra carbon dioxide dissolved in sea water will turn the oceans more acidic. Even if the marine environment is slightly alkaline, more CO2  in the seawater, means more free  H+-ions in the water. More free  Hions mean a lower pH. (The more  H+ found in a solution, the more acidic). The simple chemical formula looks like this: CO2 + H2 H2CO3. (Read more about the chemistryThe lowering of seawater pH and carbonate saturation in seawater is a result of increasing atmospheric concentrations of CO2.

Shell building and calcifying marine organisms, coral reefs and some algae and plankton production may suffer with increased acidity. The acidification of the ocean is regarded as the second very serious ecological consequence of the increasing accumulation of CO2 in the atmosphere


Coral reefs are the most diverse and beautiful of all marine habitats. Large wave resistant structures have accumulated from the slow growth of corals. The development of these structures is aided by algae that are symbiotic with reef-building corals. Coralline algae, sponges, and other organisms, combined with a number of cementation processes also contribute to reef growth. Photo: Glenn Edney

Carbon dioxide reacts chemically with sea water to produce carbonic acid

Coral reefs have exceptional biodiversity, and are now threatened by warmer oceans as well as acidification.

Ocean acidification is a change in sea water chemistry; CO2 reacts with water molecules (H2O) and forms the weak acid H2CO3 (carbonic acid). It is estimated that if CO2 continues to be released at the same rate as today, ocean acidity will increase by 170% compared to pre-industrial levels. The changes are happening at least 10 times faster than at any moment in the geological past. IAEA

The Monaco Declaration is an internationally, scientifically coordinated response to the ocean acidification problem: Monaco Declaration and Research Priorities Report Released

Important figures

  • 26%: The increase in ocean acidity from preindustrial levels to today.
  • about 170%: The projected increase in ocean acidity by 2100 compared with preindustrial levels if high CO2 emissions continue .
  • 10 times: The current rate of acidification is over 10 times faster than any time in the last 55 million years.
  • 24 million: The number of tonnes of CO2 the ocean absorbs every day.
    Ocean acidification

See videos

Google Earth ocean acidification

A Google Earth tour explores the phenomenon of ocean acidification and explains why even small changes to ocean chemistry could have profound implications for marine life and future economic activities

Ocean Acidification
– state of knowledge

World Bank, 2014, by dr Carol Turley from Plymouth Marine Laboratory (UK) summarises the current state of knowledge on Ocean Acidification.

The Other CO2 Problem: Acidic Oceans: Why Should We Care?  Perspectives on Ocean Science (Scripps)

The ocean absorbs almost half of the carbon dioxide emitted by human activities, changing its chemistry in ways that may have significant effects on marine ecosystems. Join Scripps marine chemist Andrew Dickson as he explains what we know — and what we don’t — about this emerging problem.

Acidificiation in the Arctic  

The oceans are changing. The Arctic oceans are warming, and turning more acid. Plankton at the base of the ecosystem are negatively affected and may harm productivity
Arctic Ocean Acidification (2013) – Short (3 minute) version  Full version (12 min)

NOAA Ocean Acidification – The Other Carbon Dioxide Problem

Fundamental changes in seawater chemistry are occurring throughout the world’s oceans. Since the beginning of the industrial revolution, the release of carbon dioxide (CO2) from humankind’s industrial and agricultural activities has increased the amount of CO2 in the atmosphere. The ocean absorbs almost a third of the CO2 we release into the atmosphere every year, so as atmospheric CO2 levels increase, so do the levels in the ocean. Initially, many scientists focused on the benefits of the ocean removing this greenhouse gas from the atmosphere. However, decades of ocean observations now show that there is also a downside — the CO2 absorbed by the ocean is changing the chemistry of the seawater, a process called ocean acidification. This change in the ocean’s chemistry will have profound effects on life in the ocean, and those who depend on it.

More movies:

Read more

Ocean acidity may have increased as much as 30% the last hundred years.


Home Chapter 3 3. Impacts
3.1 More water vapor
3.2 Sea level rise
3.3 Polar sea ice
3.4 Air pollution
3.5 Acidification
3.6 Health
3.7 Extreme weather
3.8 Economy
3.9 Refugees and conflicts
3.10 Glaciers
3.11 Tipping points
3.12 Biodiversity
3.13 Water
Chapter 4 4. Ecosystems