Coral reefs die from climate change. Here’s why.

Article by Isabel Key and Mina Frost.

Coral reefs have long suffered from overfishing, water pollution, and land clearing [2]. However, climate change is now the biggest threat [3]. Climate change affects coral reefs in many ways, including more frequent severe storms [4, 8], but the most serious is recurrent “coral bleaching” [8].

Corals have a close relationship with algae. The algae give the coral sugars, and in return get a safe home in the coral [5]. Under high temperatures, the coral expels the algae, leaving just the white ‘skeleton’ of the coral. This is called coral bleaching [3].

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 colour [3]. However, bleached corals are weak and vulnerable to disease [3], often resulting in their death [8].

Half of the Great Barrier Reef DIED due to bleaching in 2016 and 2017 [6, 9]. While bleaching is a natural event, climate change makes it happen more often [6, 7]. Damaged reefs can take over 10 years to recover, so bleaching one year after another may make recovery impossible [6, 8].

100% of coral is expected to die with 2°C of warming [10]. 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 [1,9]. So, when corals die, many other animals die with them. This is called an ‘extinction-cascade’ [11]. It will also have effects on humans: coral reefs currently give protection from flooding and provide food for about 500 million people [9].

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 [13].


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