Hoegh-Guldberg, 1999:

"Sea temperatures in many tropical regions have increased by almost 1°C over the past 100 years, and are currently increasing at ~1–2°C per century. Coral bleaching occurs when the thermal tolerance of corals and their photosynthetic symbionts (zooxanthellae) is exceeded. Mass coral bleaching has occurred in association with episodes of elevated sea temperatures over the past 20 years and involves the loss of the zooxanthellae following chronic photoinhibition. Mass bleaching has resulted in significant losses of live coral in many parts of the world. This paper considers the biochemical, physiological and ecological perspectives of coral bleaching. It also uses the outputs of four runs from three models of global climate change which simulate changes in sea temperature and hence how the frequency and intensity of bleaching events will change over the next 100 years. The results suggest that the thermal tolerances of reef-building corals are likely to be exceeded every year within the next few decades. Events as severe as the 1998 event, the worst on record, are likely to become commonplace within 20 years. Most information suggests that the capacity for acclimation by corals has already been exceeded, and that adaptation will be too slow to avert a decline in the quality of the world’s reefs. The rapidity of the changes that are predicted indicates a major problem for tropical marine ecosystems and suggests that unrestrained warming cannot occur without the loss and degradation of coral reefs on a global scale."

Global patterns of coral bleaching

"The mass coral bleaching event of 1998 is considered to be the most severe on record (NOAA 1998; ISRS 1998a), with bleaching affecting every geographic coral-reef realm in the world (Fig. 3). This was the sixth major episode of coral bleaching since 1979 to affect coral reefs across a significant portion of the world’s oceans.

Strong bleaching episodes coincide with periods of high SST and are associated with disturbances to the El Niño–Southern Oscillation (ENSO; Fig. 3). Most occur during strong El Niño periods, when the Southern Oscillation Index (SOI) is negative (< –5). However, some regions such as the southern parts of the Cook Islands experience bleaching in strong La Niña periods due to southward shifts in the position of the south Pacific Convergence zone and associated water masses. In 1997–98 the most extensive and intense bleaching event on record coincided with (by some indices) the strongest ENSO disturbance on record (Kerr 1999). For the first time, coral reefs in every region of the world recorded severe bleaching events (Fig. 3). In some places (e.g. Singapore, ISRS 1998a), bleaching was recorded for the first time. Many massive corals (which may live for well over 1000 years) have died as a result of the 1998 event, including some with an age of up to 700 years (ISRS 1998a); this, although in need of study, suggests that for these corals at least, conditions in 1998 were extreme relative to the previous 700 years."

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Citation and/or URL

Hoegh-Guldberg, O. 1999, Climate change, coral bleaching and the future of the world's coral reefs, Marine and Freshwater Research, 50: (8) 839-866.  © CSIRO 1999. CSIRO Publishing, Collingwood, Australia. http://www.publish.csiro.au/nid/126/paper/MF99078.htm

Spatial Coverage

Global

Temporal Coverage

Historical and projected temperatures 1800s through to 2100

Update Frequency

Not applicable 

Other Information

None