Acidification

Ocean acidification refers to a reduction in the pH of the ocean over an extended period of time, caused primarily by uptake of carbon dioxide (CO₂) from the atmosphere. For more than 200 years, the concentration of CO₂ in the atmosphere has increased due to the burning of fossil fuels and land use changes with industrialization. The ocean absorbs approximately 30 percent of the CO₂ that is released in the atmosphere, and as levels of atmospheric CO₂ increase, so do the levels in the ocean.

When CO₂ is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions. This increase causes the seawater to become more acidic and carbonate ions to be relatively less abundant. Ocean acidification is affecting the entire world’s oceans.

Effects of Acidification

Increasing CO₂ in the atmosphere due to human activities not only affects the climate; it also has direct, chemical effects on ocean waters. The oceans have absorbed between a third and a half of the CO₂ humans have released into the atmosphere since about 1850. This has slowed the rate of climate change. When CO₂ dissolves in seawater, the water becomes more acidic. The acidity of the oceans has increased by 26% since about 1850, a rate of change roughly 10 times faster than any time in the last 55 million years.

Associated chemical reactions can make it difficult for marine calcifying organisms, such as coral and some plankton, to form shells and skeletons, and existing shells become vulnerable to dissolution. The rate at which acidification occurs is a determining factor in the extent to which calcifying organisms will be able to adapt. The impacts of acidification will extend up the food chain to affect economic activities such as fisheries, aquaculture and tourism. Wherever there are marine calcifying organisms, there are risks from ocean acidification.

Effects on Human Societies

Changes in marine ecosystems have consequences for human societies, which depend on the goods and services these ecosystems provide. The implications for society include substantial revenue declines, loss of employment, and other indirect economic costs. Socio-economic impacts associated with the decline of the following ecosystem services are expected:

Food: Ocean acidification has the potential to affect food security. Commercially and ecologically important marine species are being impacted. Molluscs such as oysters and mussels are among the most sensitive groups. By 2100, the global annual costs of mollusc loss from ocean acidification could be over $100 billion for a business-as-usual CO₂ emissions pathway.

Coastal protection: Marine ecosystems such as coral reefs protect shorelines from the destructive action of storm surges and cyclones, sheltering the only habitable land for several island nations. This protective function of reefs prevents loss of life, property damage, and erosion, and has been valued at $9 billion per year.

Tourism: This industry could be severely affected by the impacts of ocean acidification on marine ecosystems (e.g. coral reefs). In Australia, the Great Barrier Reef Marine Park attracts about 1.9 million visits each year and generates more than $5.4 billion to the Australian economy.

Climate Change: Coastal and marine ecosystems are under tremendous stress from climate change. Ocean acidification, paired up with other climate impacts like warming waters, deoxygenation, melting ice, and coastal erosion, pose real threats to the survival of many marine species.

Carbon storage and climate regulation: The capacity of the ocean to absorb CO₂ decreases as ocean acidification increases. More acidic oceans are less effective in moderating climate change.