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Bleached coral reef

Ocean acidification

The ocean constitutes more than 95% of the Earth’s living space, hosting more than 220,000 known species of plants and animals (and an estimated 2 million that are unknown). While generating half of the world’s oxygen, it also serves as one of the world’s most important natural ‘carbon sinks’, absorbing more than a quarter of the carbon dioxide (CO2) released into the atmosphere by human activity. While this greatly counteracts atmospheric greenhouse gases, there are far-reaching effects on the marine environment.

When CO2 is absorbed by the ocean, it changes the chemical makeup of seawater in a process called ‘acidification’. Historically, on a pH scale of 1 to 14 (a measure of how acidic or alkaline a substance is, where 7 is neutral), the ocean has been around 8.2, which is slightly alkaline. But since the beginning of the industrial revolution, ocean pH has declined by 0.1 units – equivalent to a 30% rise in acidity, and the fastest shift in the ocean’s pH baseline for around 200 to 300 million years.

Ocean acidification has serious biological consequences. Many marine creatures have shells and skeletons of calcium carbonate (basically chalk), which can erode as pH falls. Coral reef growth is also vulnerable, especially deep-water coral, as are organisms such as swimming ‘sea butterfly’ snails (pteropods) in the polar oceans, which underpin food webs in these ecosystems. Changes in the ocean’s chemical environment can also hinder growth and reproduction for other organisms.

Exact projections of the impacts of ocean acidification are still being researched, but it is clear that ocean ecosystems, marine food-webs and biodiversity are at risk. In due course this would impact food and economic security, while affecting commercial fishing and tourism industries. Countries stand to lose an estimated $1 Trillion in total from the services provided by coral reef ecosystems alone. What’s more, as acidification worsens and the sea surface warms, the ocean becomes less effective in absorbing CO2. More in the atmosphere could intensify the impacts of climate change.

The Commonwealth Blue Charter reaffirms members’ commitment to Sustainable Development Goal #14 of the United Nations 2030 Agenda, including specific targets to address ocean acidification through enhanced scientific cooperation. New Zealand has stepped forward as the Blue Charter Champion on ocean acidification.

Fact facts:

  • Ocean acidification brought about the greatest extinction of life on Earth, when 252 million years ago Siberian volcanoes emitted lethal levels of CO2.
  • Ocean acidity will increase by 170% by 2100 compared with preindustrial levels, if present CO2 emissions continue.
  • Ocean acidification happens more rapidly in colder waters of the Arctic and Antarctic. Some species in these areas are already challenged in creating and sustaining their shells.
  • Ocean acidification prompts some plankton species to grow faster, while slowing growth for several others, disrupting the natural linkages and competition between species and putting entire ocean ecosystems at risk.
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