Ocean acidification has been called the ‘other’ CO2 problem, with ramifications of global importance, yet many people are still unaware of it. 

The oceans are a major sink for atmospheric CO2, with research suggesting they are currently absorbing 30% of the CO2 released into the atmosphere by humans. This process was initially thought to be positive, absorbing anthropogenic CO2 and reducing the effects of climate change, but it is now understood to be slowly decreasing the ocean’s pH with disastrous consequences. The lower pH decreases the availability of carbonate in the water posing a threat to calcifying organisms.

Calcium carbonate is a vital mineral used to build shells or skeletons for many calcifying marine animals, e.g., coralline algae, some phytoplankton such as coccolithophores, sea urchins, oysters, and certain other molluscs. Research has shown that live pteropods, a small snail like animal, suffer shell dissolution in sea water of the pH we can expect in 2100. Pteropods are prey for some of the most important commercial fish species, and a decline in their numbers could have serious consequences for marine fisheries. Coral reefs are associated with 25% of the world’s marine species, providing nutrition to millions of people, and form valuable coastal protection against storms. If reef building corals ability to form their calcium carbonate skeleton is weakened, this incredibly important ecosystem could be lost.

The Intergovernmental Panel on Climate Change (IPCC) suggests that by the end of this century CO2 levels could be over 800 ppm. Models indicate that the increased CO2 absorption and corresponding pH drop would be about 0.4 pH units in surface waters by 2100. Such a change has probably not occurred for more than 20 million years, and it is very unlikely the ocean ecosystems will have the ability to adapt to a change happening so fast.

To tackle ocean acidification, global CO2 emissions need to be cut drastically. Governments need to recognise this ‘other’ climate change problem and the severe adverse affects it will have on our planet and on the lives of people around the world if CO2 emissions continue unchecked. Seas At Risk is lobbying for governments to stick to their international commitment to cut greenhouse gas emissions, and for the targeting of GHG emissions from the shipping and fisheries sectors.

For more information

For details of where ocean acidification in mentioned in the IPCC's 2013 Fifth Assessment Report (AR5)

NOAA Carbon program, a good explanation of ocean acidification with diagrams

Facts, figures and films on ocean acidification by coral scientists