Essay
Reef explorer
Caribbean heat, 1985–now
A satellite has measured the sea around these reefs every day since 1985. Draw the years on one set of axes and you get a hill. The water is coolest in March and warmest at the end of September. Coral built its life around that curve.
NOAA draws a line one degree above the warmest month a reef normally sees. Above that line, coral starts to expel the algae living inside its tissue — the algae that supply most of its food and all of its color.
Pick a reef. Pull a year. Or press play and watch the heat arrive.
Sources
NOAA Coral Reef Watch, 5 km virtual station time series, through 21 August 2026 (2026 is a partial year). The notebook that draws the original figures is here.
Live hard-coral cover is from GCRMN & ICRI, Status and Trends of Caribbean Coral Reefs: 1970–2024, December 2025: about 40–50% in 1970, 28% in 1985, 15% in 2024. That is the floor this heat landed on — a handful of region-wide points, not an annual series and not a station record.