Mapping of past thermal stress on coral reefs (1998–2007) suggests that almost 40 percent of reefs may have been affected by thermal stress, meaning they are located in areas where water temperatures have been warm enough to cause severe bleaching on at least one occasion since 1998. This figure shows the estimated percentage of reefs per region that experienced thermal stress based on the satellite-detected thermal stress and coral bleaching observations shown in Map 3.2: Thermal Stress on Coral Reefs, 1998-2007.