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Then and now: Rising temperatures threaten corals

Corals can't tolerate very high temperatures, so as ocean water warms, they effectively become "sick". Thermal stress of this kind can lead to the coral becoming bleached, meaning they lose their striking colours and turn white or very pale.

The US National Oceanic and Atmospheric Administration (Noaa) says that the temperature increase in the oceans as a result of climate change is the main cause of bleaching.