Something is dying beneath Australia’s most iconic waters — and most of us haven’t noticed. Five charts trace how three decades of warming oceans have pushed the Great Barrier Reef and its marine life toward a point of no return.
The Great Barrier Reef is the size of Italy. It supports more than 1,500 species of fish, 4,000 types of mollusc, and an estimated 600 types of coral. It generates around $6.4 billion for the Australian economy every year. And since 2016, it has experienced five mass bleaching events — more than in all the decades before that combined.
This is not a story about distant futures or worst-case models. The data already exists. The warming has already happened. The bleaching is already on the record. What follows is an attempt to make that record visible — in the hope that seeing the full shape of what’s unfolding might still move us to act.
Since 1990, the seas surrounding Australia have warmed by close to 1°C above the long-run average. That might sound small. But coral reefs — built over thousands of years to tolerate a narrow temperature window — can begin to bleach when water stays just 1°C above normal for as little as four weeks. The diamonds below mark every year in which AIMS confirmed a mass bleaching event on the Great Barrier Reef. Notice how they cluster in the warmer years — and how the warmer years keep getting more frequent.
Source: Bureau of Meteorology (2024). Australian Climate Statement — annual summaries. http://www.bom.gov.au/climate/current/annual/aus/; NOAA Coral Reef Watch (2025). Thermal history products 1985–2025. https://coralreefwatch.noaa.gov/product/thermal_history/ · ◆ = AIMS-confirmed mass bleaching year.
Each bubble on this map is a bleaching event. Its colour tells you when it happened — pale blue for older events, deep red for the most recent. Its size tells you how severe the bleaching was. Zoom in, click any bubble, and you’ll see the reef name, the year, and the severity rating from AIMS monitoring surveys. The pattern is stark: events are getting more frequent, more severe, and — critically — spreading further south and west.
Source: Australian Institute of Marine Science (AIMS). LTMP bleaching dataset. https://apps.aims.gov.au/metadata/view/bba8af1a-b450-4b80-849d-a06e02b12a10; Hughes, T. P., et al. (2018). Spatial and temporal patterns of mass bleaching of corals in the Anthropocene. Science, 359(6371), 80–83. https://doi.org/10.1126/science.aan8048. Bubble size = severity rating. Colour = year. Click any bubble for details.
This chart combines four variables — SST anomaly, the proportion of reefs that bleached, reef region (colour), and the year of the survey (point size, larger = more recent). The upward slope of the trend line is not a modelling artefact. It is a consistent pattern across five regions, spanning nearly three decades of direct reef surveys. Every degree of warming beyond the climatological average pushes more reefs past the threshold at which coral expels its symbiotic algae and begins to die.
Source: Australian Institute of Marine Science (AIMS). (2025). Annual summary report of coral reef condition 2024/25. https://www.aims.gov.au/monitoring-great-barrier-reef/gbr-condition-summary-2024-25; NOAA Coral Reef Watch (2025). Thermal history products. https://coralreefwatch.noaa.gov/product/thermal_history/ · Point size encodes year of survey (larger = more recent). Colour encodes reef region. R² shown on trend line.
As surface temperatures rise, marine species don’t simply die in place — they move. Tropical fish and coral species are shifting poleward, appearing in waters south of where they’ve historically lived. Meanwhile cold-water species that anchor southern food webs are being squeezed toward Antarctica, losing habitat from both sides. This heatmap encodes observation density by latitude band and decade, making the geographic drift visible across 30 years. The upper rows get dimmer. The lower rows get darker. That is the story in two directions at once.
Source: Ocean Biodiversity Information System (OBIS). (2024). Ocean biodiversity information system. https://obis.org; Poloczanska, E. S., et al. (2013). Global imprint of climate change on marine life. Nature Climate Change, 3, 919–925. https://doi.org/10.1038/nclimate1958. Index = normalised occurrence records per 5° latitude band per decade, 1990–2024.
The final chart is a choice. Under a high-emissions scenario, sea temperatures around Australia breach 2°C above the climatological mean before 2050 — and reef coverage falls to roughly 14% of its 1990 baseline. Under a low-emissions pathway, warming slows, and reefs retain enough coverage to have a chance at partial recovery. The lines diverge after 2024. Everything to the right is still within our power to influence. The data shown to the left of the dotted line is what already happened. The data to the right is what we decide.
Source: IPCC (2021). Climate change 2021: The physical science basis, Chapter 9. https://www.ipcc.ch/report/ar6/wg1/; CSIRO (2022). Australia’s changing climate. https://www.csiro.au/en/research/environmental-impacts/climate-change/; Hughes, T. P., et al. (2021). Emergent properties in the responses of tropical corals to recurrent climate extremes. Current Biology, 31(23), 5393–5399. https://doi.org/10.1016/j.cub.2021.10.046. Solid lines = high-emissions (SSP2-4.5). Dashed lines = low-emissions (SSP1-2.6).