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Coral reefs are dying. Why?
Coral reefs have long suffered from overfishing, water pollution, and land clearing. However, climate change is now the biggest threat. Climate change affects coral reefs in many ways, including more frequent severe storms but the most serious is recurrent coral bleaching.
Corals have a close relationship with algae. The algae give the coral sugars, and in return get a safe home in the coral. Under high temperatures, the coral expels the algae, leaving just the white 'skeleton' of the coral. This is called coral bleaching.
Bleached corals aren't necessarily dead. They can survive for a short period, and if the temperature returns to normal, the algae will come back and the corals regain their color. However, bleached corals are weak and vulnerable to disease often resulting in their death.
Half of the Great Barrier Reef DIED due to bleaching in 2016 and 2017. While bleaching is a natural event, climate change makes it happen more often Damaged reefs can take over 10 years to recover, so bleaching one year after another may make recovery impossible.
100% of coral is expected to die with 2°C of warming. This would have much more severe consequences than the loss of the beautiful corals themselves: over 25% of fish species use coral reefs for food or shelter. So, when corals die, many other animals die with them. This is called an 'extinction-cascade'. It will also have effects on humans: coral reefs currently give protection from flooding and provide food for about 500 million people. .
If 2°C warming kills all coral reefs, try to imagine what 3°C or 4°C would do. This is where the Earth is headed if we don't drastically change.