The future of our oceans

Ocean pH is expected to drop by about 0.4 by the end of the century resulting in a 60% fall in calcium carbonate levels.  To prevent our oceans becoming undersaturated in aragonite it is believed that we shouldn’t let the pH drop by any more than 0.2 units in comparison with the pre industrial levels.  The change in ocean pH is almost entirely dependent on atmospheric CO_s levels, if they continue to increase, the oceans will continue to acidify.  It will be hard to reverse the acidifying trend by the end of the century as ocean chemistry works on much much larger timescales (Raven et al. 2005).  The figure below shows that with all scenarios of atmospheric CO₂ levels ocean pH falls, if the projected CO₂ levels reach around 950ppm then the ocean pH will fall to about 7.75 and the southern ocean will only be about 70% saturated in aragonite.  If the pH falls this low, it will result in a tripling in the number of H⁺ ions since the industrial revolution.  This rate of change is faster than anything seen over the last few hundred thousand years and at least 100 times higher than anything seen since then (Raven et al. 2005). 

 Figure 1.  Atmospheric CO₂ concentrations, global ocean pH and the surface saturation state of aragonite for IPCC emission scenarios for 2000-2100. (IPCC, 2007).

References:

IPCC (2007). ‘Climate change 2007: the physical science basis.

Raven , J. Caldeira, K. ELderfield, H. Hoehg-Guldberg, O. Liss, P. Riebesell, U. Shepherd, J. Turley, C. Watson, A. (2005). ‘Ocean acidification due to increasing atmospheric carbon dioxide’, The Royal Society: London.