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OceansSeverity: Critical

Marine heatwaves and coral bleaching on the Great Barrier Reef

Repeated mass bleaching events driven by ocean warming are the greatest threat to the reef.

Great Barrier Reef · Australia

01 · The problem

What is happening

When sea temperatures stay unusually high, corals expel the symbiotic algae that provide much of their energy and colour, and turn white. Prolonged or severe bleaching kills corals. The Great Barrier Reef Marine Park Authority has documented mass bleaching events in 2016, 2017, 2020, 2022 and 2024, with the shortening gap between events leaving less time for recovery. The Authority's 2024 Outlook Report identifies climate change as the greatest threat to the reef's long-term outlook. NOAA's Coral Reef Watch monitors heat stress globally.

Critical severity. Severe, persistent harm to health, ecosystems or livelihoods. Severity is descriptive editorial metadata summarising documented effects. It is not a measured index or a score.

02 · Causes

Why it is happening

  1. 01

    Ocean warming

    Rising sea temperatures from greenhouse gas emissions increase marine heatwave frequency and intensity.

  2. 02

    El Niño and regional variability

    Climate patterns can amplify summer heat on the reef.

  3. 03

    Ocean acidification

    Absorbed carbon dioxide reduces the ability of corals to build skeletons.

03 · Impacts

Who and what it affects

  1. 01

    Coral mortality

    Severe bleaching kills corals across large areas of reef.

  2. 02

    Biodiversity loss

    Fish and other species that depend on coral habitat decline.

  3. 03

    Tourism and livelihoods

    Reef tourism supports many jobs in Queensland.

  4. 04

    Cultural impacts

    Traditional Owners have deep cultural connections to Sea Country.

04 · Solutions

Documented approaches

  1. Global emission reductions

    Limiting warming is the only way to reduce the underlying driver.

    Expected effectDetermines the long-term future of coral reefs worldwide.

  2. Reef 2050 Long-Term Sustainability Plan

    Joint Australian and Queensland government plan for reef management.

    Expected effectCoordinates action on water quality, protection and restoration.

  3. Reef restoration and adaptation research

    Coral breeding, larval reseeding and heat-tolerance research.

    Expected effectMay help local recovery; cannot replace emission cuts.

  4. Marine park zoning

    No-take zones across a significant share of the Marine Park.

    Expected effectSupports fish populations and ecosystem resilience.

Explore an illustrative What-If

05 · Key indicators

What can be measured

Mass bleaching events
2016, 2017, 2020, 2022, 2024

Documented by the Great Barrier Reef Marine Park Authority.

06 · Sources

Where this comes from

  1. [1]Great Barrier Reef Outlook Report 2024Great Barrier Reef Marine Park Authority · Oct 2024gbrmpa.gov.au(opens in a new tab)
  2. [2]Australian Institute of Marine ScienceAIMSaims.gov.au(opens in a new tab)
  3. [3]Coral Reef WatchNOAAcoralreefwatch.noaa.gov(opens in a new tab)

Links open the publishing organisation's site. Some point to the publisher's main page, where the named report or dataset can be found.

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