Corals are extremely sensitive to water that is too warm - even temperatures just 1°C above the highest average summertime temperature. If corals bathe in water above this critical threshold for just four weeks (or at higher temperatures for even shorter durations), the accumulated heat stress can induce coral bleaching, a condition where coral polyps expel their beneficial algae and starve. Bleached coral turns white and can die or remain weakened for years. Although coral can bleach for reasons other than warm water, in recent decades a worrisome pattern has emerged. Episodes of global coral bleaching are becoming more frequent. These widespread events are thought to be among the earliest distinct signs of climate change's effects on Earth's organism
According to NOAA scientists, 2010 tied with 2005 as the warmest year on record. Throughout the year, satellite monitoring from NOAA's Coral Reef Watch
program detected that sea-surface temperatures exceeded the bleaching threshold for several weeks in various regions of the world. Scientists and reef managers soon began to observe excessive bleaching in many areas in which it was predicted by satellite. The 2010 global bleaching event was the second ever recorded, with the first occurring during 1997-98.
The following datasets from the flat-screen visualization are included for spherical display. The movie contains:
A global image showing the location of reef-building corals (indicated in blue) between 35°N and 35°S latitudes. The location data are from the World Resource Institute's Reefs at Risk Revisited report
A 1 year (January to December 2010) time series of Degree Heating Weeks data from the NOAA Coral Reef Watch program. The dataset is based on sea-surface temperature measurements taken every three days from the AVHRR sensor on NOAA's polar-orbiting satellites. The Degree Heating Weeks dataset shows how much heat stress has accumulated in an area over the past 12 weeks. Scientists have calculated thresholds of accumulated heat stress that puts corals at risk for bleaching and death. These thresholds are represented by the indicated colors.
A single Degree Heating Weeks image that represents the accumulated heat stress for all of 2010.
A map indicating observations of bleached and dead coral in 2010. These observations were reported to ReefBase and the NOAA Coral Reef Watch program.
Coral Reefs in Hot Water was produced in collaboration with the NOAA National Environmental Satellite, Data, and Information Service (NESDIS), the NOAA Climate Program Office, and the Coral Reef Watch program at the NOAA National Environmental Satellite, Data, and Information Service. The flat-screen visualization and associated educator resources are available at http://sciencebulletins.amnh.org/?sid=b.v.coral_reefs.20110511