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, the ocean has been around 8.2, which is actually slightly alkaline. (Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic, or alkaline.) But since the beginning of the industrial revolution, ocean pH has declined by 0.1 units – equivalent to a 30 per cent 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 become harder and harder to grow, and can erode as pH falls. Acidification affects the ability of shellfish, urchins, corals and plankton to build and maintain their shells and calcium carbonate structures. It also affects the behaviour of some fish - for example, their ability to detect predators.  This in turn leaves many species more vulnerable to damage and reduces their resilience.

Coral reef growth is also vulnerable, especially deep-water coral.  So are organisms such as swimming ‘sea butterfly’ snails (pteropods) in the polar oceans, which underpin food webs in their ecosystems. Changes in the ocean’s chemical environment hinder the growth and reproduction of many other organisms as well.

Ocean acidification is increasing, exacerbating the impact of other climate change phenomena. At particular risk are communities that depend on fish and shellfish or rely on coral reefs for protection. Small island developing states (SIDS) are especially vulnerable.

the increase of ocean acidity by 2100, from preindustrial levels, if present CO2 emissions continue

Exact projections are still being researched, but it is clear that ocean ecosystems, marine food-webs and biodiversity are at risk from ocean acidification. Commercial fishing and tourism are at risk, as is food and economic security over the longer term.  Countries stand to lose an estimated $1 trillion from coral reef ecosystems alone. As acidification worsens and the sea surface warms, the ocean becomes less effective in absorbing CO2, leaving more in the atmosphere and intensifying the impacts of climate change.

of all the CO2 emitted by human activities is absorbed by the ocean each year

New Zealand will champion the Ocean Acidification Action Group –improving the capacity of Commonwealth countries to address the impact of ocean acidification, particularly in small-island developing states.

The Action Group will share knowledge, experience and best practice the impact of ocean acidification and how to address it. It will focus on improving our understanding of:

  • the impact of ocean acidification;
  • its drivers (other than carbon dioxide), especially in coastal habitats;
  • modelling and forecasts; and
  • mitigation, adaptation and resilience measures.

The Action Group will also work towards:

  • improving abilities to tackle technical, social and governance challenges;
  • developing cross-Commonwealth connections, as well as linkages with other international ocean acidification networks;
  • increasing observational capacity/technical capability;
  • strengthening stakeholder engagement and bridging gaps among scientists, communities and policy-makers, to help facilitate the development of national and international policy; and
  • increasing public awareness/education about ocean acidification and its impacts.