The Bleaching Reef
A living structure visible from space is turning white.
Corals live in a delicate partnership with algae that give them colour and food. When the ocean overheats, corals expel the algae and turn bone-white. Prolonged bleaching kills them. The Great Barrier Reef has suffered five mass bleaching events since 2016.
Mass bleaching events
7 since 1998
5 of them since 2016
~50%
Shallow coral lost
since 1995
1,500+
Species supported
fish species alone
+1-2°C
Bleaching threshold
above summer max, for weeks
99%
Reefs at risk at 2°C
of the world’s coral
Marine heat stress (Degree Heating Weeks)
DHWWhat's happening
- ▸Reefs protect coastlines from waves and storms; their loss exposes communities.
- ▸Tourism and fisheries worth billions and tens of thousands of jobs are at stake.
- ▸Surviving corals are being bred for heat tolerance and replanted - a race against time.
What helps
- Limiting warming to 1.5°C keeps perhaps 10-30% of reefs; 2°C leaves almost none.
- Cutting local stressors: agricultural runoff, overfishing and coastal pollution.
- Assisted evolution and coral nurseries buy threatened reefs time.
How it unfolded
- 1998
First mass bleaching during a strong El Niño.
- 2016
Catastrophic bleaching kills ~30% of corals.
- 2017
Back-to-back bleaching strikes the central reef.
- 2020
First bleaching driven without an El Niño.
- 2024
Fifth mass event in eight years confirmed.
Next frontline
The Horn of Africa