As the amount of CO2 in our atmosphere steadily imcreases over time, so do the levels in the ocean. Currently 25% of atmospheric CO2 enters the oceans (Hoegh-Guldberg et al. 2007). Oceans taking in CO2 could be said to be a natural sink for the excess emissions, however, as the gas in the sea increases so does the concentration of [H+] ions decreasing the pH level. When the pH level drops the ocean becomes more acidic. It is thought by Orr et al. (2005) that by the end of the century the pH value would have dropped by 0.3-0.4 units. The decrease in pH will have direct effects on the calcium carbonate structures from which corals rely on. The lack of carbonate available in the system is due to the reactions that take place between carbonic acid and water to form bicarbonate. This essentially reduces the available carbonate in the water which is available to systems to form reefs (Hoegh-Guldberg et al. 2007). Figures from Hoegh-Guldberg (2007) suggested that coral growth and calcification rates decrease byt 40% with doubling of atmospheric carbon dioxide. The rates of decrease are caused by ‘inhibition of aragonite formation’ (Hoegh-Guldberg 2007).
Globally average conditions have been used in predictive models of climate change, therefore, on a local scale, areas may become more or less affected.