Acidification of the oceans
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Ocean acidification is a new and looming threat that could undermine the marine food web, and preclude the coral development upon which much sustainable tourism depends. The dissolution of carbon dioxide (CO2) into seawater leads to considerable acidification and changes to the geobiochemical carbonate balance. The oceans have absorbed one third of anthropogenic CO2 emissions, which has caused significant acidification. These emissions affect the marine environment directly, in addition to any other impacts that occur due to climate change.
The continuation of current trends will lead to a level of acidification without precedent for several million years, and that will last for millennium. The effects on marine ecosystems cannot be forecast exactly. There is the risk of profound changes to the food web, as calcification of marine organisms may be precluded, or in some cases prevented. On a global level, there are parallels to problems with the acidification of lakes and rivers by acid rain that occurred in the 1970s and 1980s.
Acidification, as well as sea level rise, will remain for the next few thousand years. Sea level rise is generally understood as a slower but predictable impact of climate change. Over time, sea level rise may change coastal, island and marine ecosystems, particularly if tourist development and transportation infrastructure prevents these ecosystems from moving inland. In addition, sea level rise will affect fresh water systems, one impact will be increasing salt water intrusion in aquifers and estuaries, particularly depleted aquifers or subsiding estuaries.
Acidification of the ocean and global environmental change is linked to carbon dioxide emissions. According to a recent report, published by the UK’s Royal Society (2005), atmospheric concentrations of CO2, the main greenhouse gas, increased from 280 parts per million (ppm) in 1750 to over 375 ppm today. Absorption of CO2 by the oceans has lowered the average pH of the oceans by about 0.1 units from pre-industrial levels. If CO2 emissions continue according to current trends, this could lower the average pH of the surface oceans by between 0.14 and 0.35 units by 2100 (IPCC 2007). Ocean acidification decreases the ability of the ocean to absorb additional atmospheric CO2, which implies that future emissions of CO2 are likely to lead to more rapid global warming.
Increasing acidity of the oceans reduces the formation and speeds up the breakdown of essential shell forming carbonates such as magnesian calcites (from coralline algae), aragonite (from corals and molluscs such as pteropods), and calcite (from certain species of phytoplankton such as coccolithophorids and foraminiferas). If present trends in anthropogenic CO2 continue to rise for the next several hundred years, the Royal Society (2005) suggests that this may have severe implications for many species of calcium carbonate (CaCO3) shell–forming organisms, such as coral reefs, deep-water reef ecosystems, and calcifying phytoplankton and foraminiferas. Ocean acidification may even affect the coldwater coral reefs before they have been fully explored (Royal Society 2005;Guinotte et al. 2006).
- The Royal Society (2005) Ocean acidification due to increasing atmospheric carbon dioxide. Policy Document 12/0
- IPCC (2007) Climate Change 2007: The Physical Science Basis (Executive summary) Intergovernmental Panel on Climate Change, Geneva, Switzerland
- Guinotte JM, Orr J, Cairns S, Freiwald A, Morgan LE, George R (2006)- Will human-induced changes in seawater chemistry alter the distribution of deep-sea scleractinian? Frontiers in Ecology and the Environment 4, 141-146
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