The Great Barrier Reef Marine Park Authority lists climate change as the single biggest long-term threat to the health of the Great Barrier Reef. Rising temperatures, ocean acidification, and extreme weather are placing coral reefs around the world under immense stress – threatening their health, biodiversity, and long-term survival.

Climate change causes many indirect as well as direct issues that affect reef health. A few key direct impacts are outlined below:

What is Coral Bleaching?

Corals have a symbiotic relationship with a tiny algae (zooxanthellae) that live inside their tissues and give them colour and energy. When waters become too warm for too long, corals expel the algae, turning white – this is called bleaching.

Bleached corals are not dead, but they are stressed and more vulnerable to disease and death. If temperatures return to normal quickly, corals can recover. But bleaching events, especially repeated ones, weaken entire reef systems.

• Bleaching events are becoming more frequent and severe due to climate change.

Ocean Acidification

Burning fossil fuels not only warms the planet, but it also increases the amount of carbon dioxide (CO2) absorbed by the ocean. This causes ocean acidification, which weakens coral skeletons and makes it harder for corals and other calcifying marine animals (like clams and snails) to build their shells. Over time, it can actually reverse the calcification process and begin to dissolve coral reefs.

• Makes coral growth slower
• Reduces reef structural strength
• Can eventually erode reef systems

Extreme Weather

Climate change also makes extreme weather events – such as marine heatwaves, storms, and floods – more frequent and intense. This can:

• Break or damage coral structures
• Reduce water quality through runoff
• Stress or displace marine life
• Decrease the overall resilience of reefs