Overview
The following information is drawn from the Great Barrier Reef Outlook Report 2024 (Outlook Report).
Four main factors influence the Great Barrier Reef’s values:
- climate change
- coastal development
- land-based runoff
- direct use.
Climate change due to human activities is a global issue affecting all ecosystems and their services and benefits. Climate change is the most pervasive and persistent influence on the Great Barrier Reef.
The most immediate and current threats from climate change are:
- ocean warming, resulting in thermal extremes that cause mass mortality and sublethal impacts in corals and other organisms
- extreme rainfall events that reduce water quality.
Other impacts of climate change, such as sea-level rise and ocean acidification, are also increasingly affecting the Great Barrier Reef, but not with the same immediate and Reef-wide impact as sea temperature increases.
The present-day frequency and severity of climate change-related impacts are increasing and interacting with the other key threats, compounding their effects.
A primary concern is the vulnerability of the Great Barrier Reef’s key habitats and habitat-forming species, such as corals, seagrasses, mangroves and wetlands, based on their roles in supporting ecosystem resilience and maintaining biodiversity.
Coral reef habitats and coral-dependent species are among the most vulnerable to sea temperature increases. Proximity to their thermal limits brought about by ocean warming signifies a precarious condition for the Great Barrier Reef's corals, as seen by the four mass coral bleaching events since 2016.
In 2016 and 2017, the Great Barrier Reef experienced two consecutive summers of severe mass coral bleaching, which occurred towards the end of the most severe, widespread, and longest-lasting global coral bleaching event on record. These bleaching events caused widespread coral mortality across the Great Barrier Reef.
Between 2018 and 2022, coral cover in offshore reefs recovered rapidly, led by fast-growing plating and branching corals. Limited cyclone activity and flood impacts also facilitated further recovery, as did mitigation of further coral losses from the ongoing crown-of-thorns starfish outbreak through targeted control actions across much of the Great Barrier Reef Marine Park.
Recovery occurred despite a further, albeit less severe, mass coral bleaching event in 2020. It continued until the trend plateaued in response to the cumulative effects of the 2022 mass coral bleaching event and localised crown-of-thorns starfish impacts. Another widespread mass coral bleaching event unfolded in the Great Barrier Reef in early 2024.
The Great Barrier Reef’s key habitats have a natural resilience against acute physical disturbances, such as cyclones, intense rainfall, freshwater flood plumes, and heat waves. However, climate change is exacerbating both acute and chronic disturbances, shrinking recovery windows and affecting ecological processes that underpin ecosystem resilience.
Key indicators like seawater temperatures follow ongoing trajectories directly related to global warming. Climate change impacts are forecast to become more frequent, severe, and widespread, and will amplify the impacts of other threats. The resulting trend is one of increasing cumulative impacts on the Region’s ecological, heritage, economic and social values.
Results
See the links below the tables for the Great Barrier Reef Outlook Report 2024’s full assessment information and methods.
