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Four global bleaching events — and all four have happened since 1998
Mass coral bleaching across whole oceans was unknown to science before 1998. There have been four global-scale events since — and the gap between them is shrinking. The fourth is the largest ever documented by reef area.
What does Degree Heating Week mean?
One DHW = one week at 1°C above the reef’s normal summer peak. NOAA uses 4 / 8 / 12+ as bleaching and mortality thresholds.
Where is heat stress worst today?
Each dot is a NOAA Coral Reef Watch Virtual Station. Color = 7-day max Bleaching Alert Area (0–5); size = current degree heating weeks.
Your nearest monitored reef
Finding your nearest reef station…
Top severe reefs — heating the fastest
Ten highest DHW stations today. Dashed lines = 4 / 8 / 12 °C-weeks. Sparklines use ~90-day history when available.
How does today compare to past global bleaching events?
Recent composite stress index from our snapshot — the four documented global mass-bleaching events are listed in the panel above.
Does El Niño raise bleaching risk?
Strong El Niños have lined up with global bleaching — 1997–98, 2014–17, and 2023–24. Current Pacific state from our ENSO sibling monitor.
Coral bleaching news
What drives this
- Ocean heat →Stored ocean heat is the long-run engine of reef heat stress.
- Marine heatwaves →Acute heat spikes push reefs past their bleaching threshold.
- ENSO / El Niño →Strong El Niños lined up with all four global bleaching events.
What this drives
- Coastal flood risk →Living reefs are natural breakwaters; losing them exposes coasts to surge.
How we know this
- Source: NOAA Coral Reef Watch Virtual Stations — daily degree heating weeks (DHW) and 7-day max Bleaching Alert Area (BAA).
- Update cadence: We download NOAA’s public station files daily; values are typically one day behind real time.
- Time coverage: Map and KPIs use the latest day in each station file; sparklines show the trailing ~90 days in our snapshot.
- Methods: Point stations (~150 in this build), not a full 5 km satellite grid. BAA levels follow NOAA’s 0–5 scale.
- Uncertainty: Satellite heat stress does not prove coral death on the seafloor — many reefs lack diver surveys.
- Limitations: “Nearest reef” uses your approximate location; open-ocean stations may be far from your dive site. ENSO panel reads a sibling JSON file, not live CPC API.
- Primary data: NOAA CRW Virtual Stations · How this page is built