Global warming and increased carbon emissions have increased the numbers of El Niño events in recent years. El Niño events are sudden temperature increases in the eastern part of the Pacific Ocean. These can result in changing weather patterns as well as major weather events around the world. However, El Niño events are not usually linked to coral bleaching, another major issue.
Coral bleaching is the process by which a coral sheds its algae and becomes completely white. Because the coral and algae have a symbiotic relationship, they depend on each other to survive, to some extent. Bleached corals are also subject to higher mortality rates when algae does not return to the coral and it is thus deprived of its main food source and left susceptible to disease.
Sources: https://ore.exeter.ac.uk/repository/bit … sequence=1 and https://oceanservice.noaa.gov/facts/coral_bleach.html