Thus the geographic extent, increasing frequency and regional severity of mass bleaching events are likely a consequence of a steadily rising baseline of marine temperatures. The scale of coral disease and death in 1998 has been noted in several recent reports by international scientific groups, but the State Department study is the most complete documentation of the problem. It is also the most forceful pronouncement by federal officials linking the phenomenon to climate change. Other scientists, however, say they aren't convinced of a link to global warming, especially because the ocean warming pattern doesn't match climate forecasting models. Coral reefs are the foundation of one of Earth's most productive and diverse ecosystems, providing food and shelter for at least 1 million species of animals, plants and microbes.
Reefs yield a host of benefits for humans, including food, medicines and tourism income.
In recent decades, scientists have documented a worldwide decline in the health of reefs because of coastal pollution and destructive fishing practices. The gradual degradation may have left corals more vulnerable, experts say. Corals are tiny animals whose immense colonies form the small layer of living tissue on tropical reefs. They secrete a limestone skeleton, which over generations forms the framework of reefs. Bleaching results from a disruption in the balance between the coral and tiny algae plants that live inside the coral tissue.