Coral reef systems protect coastal areas, in some cases whole islands, from the destructive power of the sea and wind, and provide a haven for marine life. Dying corals expose these coastal areas to severe sociol-economic effects. Whilst corals are stressed by pollution and sedimentation, they have indicated their particular sensitivity to sudden sea temperature changes. They thrive in waters up to 28 degrees Celsius, but if exposed to temperatures just 2 to 3 degrees Celsius higher - even for two or three days - the algae are expelled from the coral.

In 1991, leading coral reef expert John Ogden, Director of Florida Institute of Oceanography, suggested that nearly every reef system in the world was suffering from coral bleaching, along the coasts of more than 20 countries, including Australia, China, Japan, Panama, Thailand, Malaysia, the Philippines, India, Indonesia, Kenya, the Red Sea states, Puerto Rico, Jamaica, and the Bahamas.

Corals will inevitably be among the first organisms to show the consequences of a sustained increase in sea surface temperatures, because of the fragile temperature dependence of the tiny algae, called zooxanthellae, which live in the coral's cells. The coral's colour and most of its food come from these algae, so without them the coral cannot grow.

Reefs already under assault:

1990:

• US coral experts report unprecedented coral bleaching in the Caribbean, primarily associated with warmer than usual sea temperatures.

1991:

• Mass bleaching and a 50 per cent mortality rate are reported on corals in the Straits of Hormuz, Arabian Gulf.

1991:

• 85 per cent bleaching is reported on French Polynesian reefs.

1991:

• Coral reefs in Thailand are reported to be losing colour down to 8 metres. Water in the region has been 2 degrees Celsius warmer than usual.

1994:
• A severe coral bleaching episode is reported in the Tahiti lagoon, possible linked to warmer-than-normal water. Local experts predict 100 per cent bleaching by the end of May 1994.