CO2, Global Warming and Coral Reefs
Part 1: Indirect Threats
Coral bleaching ranks as probably the most frequently cited indirect negative consequence believed to result from CO2-induced global warming. It is a phenomenon that is characterized by a loss of color in certain reef-building corals that occurs when the algal symbionts, or zooxanthellae, living within the host corals are subjected to various stresses and expelled from them, resulting in a loss of photosynthetic pigments from the coral colony. If the stress is mild, or short in duration, the affected corals often recover and regain their normal complement of zooxanthellae. However, if the stress is prolonged, or extreme, the corals eventually die, being deprived of their primary food source.
We begin our review of the subject by discussing, in section 1 below, the many suspected causes of coral bleaching, almost all of which have been attributed, in one way or another, to CO2-induced global warming. Then, in section 2, we examine the possibility that corals can adapt to the various environmental threats they face, after which we explore in section 3 whether or not the widespread bleaching events seen in recent decades are indeed caused by global warming, or if there might be other factors at play that may be of equal or even greater importance. Lastly, in section 4, we conclude our discussion of the major indirect threats facing modern coral reefs by examining the threat of rising sea levels, which the Intergovernmental Panel on Climate Change predicts will occur over the course of the 21st Century.