Coral Bleaching and Global Climate Change: Scientific Findings and Policy Recommendations

In 1998, tropical sea surface temperatures were the highest on record, topping off a 50-year trend for some tropical oceans. In the same year, coral reefs around the world suffered the most extensive and se- vere bleaching (loss of symbiotic algae) and subsequent mortality on record. These events may not be attrib- utable to local stressors or natural variability alone but were likely induced by an underlying global phe- nomenon. It is probable that anthropogenic global warming has contributed to the extensive coral bleaching that has occurred simultaneously throughout the reef regions of the world. The geographic extent, increasing frequency, and regional severity of mass bleaching events are an apparent result of a steadily rising baseline of marine temperatures, combined with regionally specific El Nino and La Nina events. The repercussions of the 1998 mass bleaching and mortality events will be far-reaching. Human populations dependent on reef services face losses of marine biodiversity, fisheries, and shoreline protection. Coral bleaching events may be- come more frequent and severe as the climate continues to warm, exposing coral reefs to an increasingly hos- tile environment. This global threat to corals compounds the effects of more localized anthropogenic factors that already place reefs at risk. Significant attention needs to be given to the monitoring of coral reef ecosys- tems, research on the projected and realized effects of global climate change, and measures to curtail green- house gas emissions. Even those reefs with well-enforced legal protection as marine sanctuaries, or those managed for sustainable use, are threatened by global climate change.