The highest sea surface temperatures ever recorded, related both to the 1997–98 El Nino/Southern Oscillation and to global warming1, caused severe bleaching of corals worldwide in 1998 (ref. 2). This thermal anomaly induced mass mortality of scleractinian corals on lagoonal reefs in Belize, the first time that a coral population in the Caribbean has collapsed completely from bleaching. Cores extracted from the Belizean reefs showed that these events were unprecedented over at least the past 3,000 years.