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- Future Climate Change
- Atmosphere
- Temperature
- Precipitation and Storms
- Sea Levels
- Ocean Acidification
Future Ocean Acidification
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Key Points:
- The acidity of the oceans has increased since pre-industrial times and will continue to increase in coming decades, due to human-generated carbon dioxide (CO2) emissions.
- The pH of the surface oceans could decline by up to 0.5 units by 2100 if CO2 emissions continue to increase on present trends.
- Increasing oceanic acidity will adversely affect the health of corals and other marine calcifiers (e.g., marine snails).
Figure 1: Atmospheric CO2 concentrations (a) global ocean pH (b) and the surface saturation state of aragonite(c) for IPCC emission scenarios (plausible CO2 emission scenarios that vary based on different assumptions for global energy use and socioeconomic changes) for 2000-2100. The dashed line represents the 100 percent line separating over- and under-saturated regions. The Southern Ocean could be aragonite under-saturated by about 2050 and this could make it difficult or impossible for aragonite-dependent corals and other marine calcifiers to form shells.
Source: IPCC, 2007b
Due to increasing concentrations of carbon dioxide in the atmosphere, ocean acidity has increased since pre-industrial times (IPCC, 2007a). The ultimate extent of acidification will depend largely on the trajectory of future CO2 emissions, but a certain amount of additional acidification is essentially irreversible during our lifetimes, due to the time scales at which oceanic chemistry functions (Raven et al, 2005). If CO2 emissions from human activities continue at present trends, the pH of the surface oceans may decline by up to 0.5 units by 2100 (Raven et al, 2005). This increase in ocean acidity would correspond to a three-fold increase in the concentration of hydrogen ions from pre-industrial times, probably representing a level of acidification not experienced for at least hundreds of thousands of years. The increase in acidity would also imply a rate of change that is likely at least 100 times higher than the previous maximum rate during this time period (Raven et al, 2005).
As ocean acidification increases, the availability of calcium carbonate minerals such as aragonite that are needed by marine calcifiers for shell and skeleton formation will decline (see Figure 1). Decreased availability of calcium carbonate will lead to increases in both the energetic costs of shell building and the rate at which shells dissolve (Raven et al, 2005). As a result, corals and other marine calcifiers (e.g. marine snails, shrimp, and crabs) will be adversely affected by ocean acidification (IPCC, 2007a). Other groups of marine organisms will be impacted in ways that are not yet fully understood but could significantly impact ecosystem structure and productivity (Raven et al, 2005).
It is important to note that ocean acidification is not a result of climate change, but is rather a direct consequence of the increased CO2 levels that also cause climate change. Ocean acidification will, however, affect future climate change by causing a decline in the ocean’s capacity to absorb increasing atmospheric CO2 (IPCC, 2007b).
References
- IPCC, 2007a: Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E.Hanson, Eds., Cambridge University Press, Cambridge, UK, 976pp. - IPCC, 2007b: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning (eds.)].
- Raven, J., K. Caldeira, H. Elderfield, O. Hoegh-Guldberg; P. Liss, U. Riebesell, J. Shepherd, C. Turley, and A. Watson. 2005. Ocean Acidification due to Increasing Atmospheric Carbon Dioxide . The Royal Society, London, UK.