Ocean acidification (in IPCC 2014 Report)

Anthropogenic ocean acidification and global warming share the same primary cause, which is the increase of atmospheric CO2 (Figure OA-1A; WGI, Section 2.2.1). Eutrophication, loss of sea ice, upwelling and deposition of atmospheric nitrogen and sulfur all exacerbate ocean acidification locally. Chemistry and Projections The fundamental chemistry of ocean acidification is well understood (robust evidence, high agreement). Increasing atmospheric concentrations of CO2 result in an increased flux of CO2 into a mildly alkaline ocean, resulting in a reduction in pH, carbonate ion concentration, and the capacity of seawater to buffer changes in its chemistry (very high confidence). The changing chemistry of the surface layers of the open ocean can be projected at the global scale with high accuracy using projections of atmospheric CO2 levels (Figure CC-OA-1B). Observations of changing upper ocean CO2 chemistry over time support this linkage (WGI Table 3.2 and Figure 3.18; Figures 30-8, 30-9). Projected changes in open ocean, surface water chemistry for the year 2100 based on representative concentration pathways (WGI, Figure 6.28) compared to pre-industrial values range from a pH change of –0.14 units with Representative Concentration Pathway (RCP)2.6 (421 ppm CO2, +1°C, 22% reduction of carbonate ion concentration) to a pH change of –0.43 units with RCP8.5 (936 ppm CO2, +3.7ºC, 56% reduction of carbonate ion concentration). Projections of regional changes, especially in the highly complex coastal systems (Sections,, in polar regions (WGI Section 6.4.4), and at depth are more difficult but generally follow similar trends. (…) Gattuso J.-P., Brewer P., Hoegh-Guldberg O., Kleypas J. A., Pörtner H.-O. & Schmidt D., 2014. Ocean acidification. In: Field C. B., Barros V. R., Dokken D. J., Mach K. J., Mastrandrea M. D., Bilir T. E., Chatterjee M., Ebi K. L., Estrada Y. O., Genova R. C., Girma B., Kissel E. S., Levy A. N., MacCracken S., Mastrandrea P. R. & White L. L. (Eds.), Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, pp. 129-131. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press. Report chapter.

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