Coral bleaching occurs when water temperatures rise just one degree above average, causing coral polyps to expel their microscopic algae partners. This expulsion triggers a chain reaction where the coral loses up to 90 percent of its energy supply and reveals the white calcium carbonate skeleton beneath.
The Intergovernmental Panel on Climate Change reported in 2022 that mass bleaching frequency has increased sharply worldwide since the early 1980s. Between 1979 and 1990, sixty major episodes of coral bleaching occurred affecting reefs in every part of the world.
Coral reef services contribute approximately $2.7 trillion annually to the global economy including $36 billion from tourism alone. A study found that commercial value decreases by almost 4 percent every time coral cover drops by 1 percent due to lost ecotourism revenue.
In 2016, over 70 percent of coral reefs around the world became damaged while Japan's Iriomote Island saw about 94 percent of corals bleach. The Maldives lost more than 60 percent of its coral cover in 2016 alone and Thailand experienced a severe mass bleaching which affected 70 percent of coral in the Andaman Sea.
The US National Oceanic and Atmospheric Administration monitors for bleaching hot spots where sea surface temperature rises 1°C or more above average using Degree Heating Week metrics. Satellite remote sensing detects worldwide bleaching events earlier than ground observations could and NOAA Coral Reef Watch sends alerts to research scientists and managers via their website covering 190 reef sites globally.