While the threat of ocean acidification is not strictly a climate change issue, but rather another manifestation of burgeoning levels of carbon dioxide emissions, many of us discuss the issue in our CC courses for a number of reasons, including the potential synergism of climate change and acidification impacts in the marine environment, and the implications for focusing on reductions of carbon dioxide vs. the proverbial basket of GHG gases. Here’s a very good article in this context: J.E.N. Veron, Mass Extinctions and Ocean Acidification: Biological Constraints on Geological Dilemmas, 27 Coral Reefs 459-472 (2008).
Among the author’s key conclusions on the potential impacts of current trends of ocean acidification:
- There have been several historical eras in which most reefs have been lost, and it has taken millions of years for reappearance. For example, during the Ordovician extinction spasm, living reefs disappeared and did not reappear for another 4-6 million years; the period was even longer after the Triassic mass extinction, 6-8 million years;
- In the context of acidification impacts on coral reefs:
- Fast-growing branching species, especially Acropora and ecological equivalents, would likely be most affected by ocean acidification, the very species that make reefs resilient to physical damage, [including phenomena that are likely to be exacerbated by climate change, violent weather events];
- Acidification is now believed to have been the most probably cause of both mass coral extinctions in the past, as well as the abiding factor preventing reefs from recovering for millions of years. However other factors, e.g. low light, bleaching and deteriorating water quality have a role to play;
- Unlike the enhanced greenhouse temperature effect of rising levels of carbon dioxide, the acidification effect of carbon dioxide will not reverse for a tremendously long time, until they are neutralized by the dissolving of calcium carbonate rocks and weathering of rocks on land
- Should carbon dioxide levels reach 800 ppm later this century [a very credible scenario currently], ocean pH levels will decline by an average of 0.4 units, and dissolved carbonate ion concentrations will have decreased by almost 60%. “At that point all the reefs of the world will be eroding relicts;”
- In a few centuries, ocean pH will drop to a point where other profound threats to the marine environment will be manifested, including anoxia, at which point Earth could enter its six mass extinction.