Climate change pressure on the Great Barrier Reef

Key finding

Climate change remains the most serious threat to the Great Barrier Reef. It is already affecting the Reef and is likely to have far-reaching consequences in the decades to come. Sea temperatures are on the rise and this trend is expected to continue, leading to an increased risk of mass coral bleaching; gradual ocean acidification will increasingly restrict coral growth and survival; and there are likely to be more intense weather events.

Climate change has both direct and indirect effects on the animals and plants that make the Great Barrier Reef so special and the ecosystem processes required to maintain their habitat.

Over the 30 years to 2010, mean annual global carbon dioxide levels in the atmosphere increased from 338 parts per million to 388 parts per million. In the four years to 2014, the amount rose to 397 parts per million: a recent 2015 monthly average was more than 400 parts per million. Accelerated increases in carbon are predicated and will directly change the reef’s ecosystem.

Increasing levels of atmospheric carbon dioxide and other gases add to the ‘greenhouse effect’, raising air temperatures with flow-on impacts of increased sea temperatures, rising sea levels and a gradual change in the acid-base balance (pH level) of sea water as carbon dioxide is absorbed. Corals and the shells of animals are expected to be affected by the changing water chemistry.

More severe weather–more intense storms and monsoonal rainfall–is expected, with direct and indirect impacts on the marine environment.

As the climate changes, coral bleaching is predicted to become more frequent and severe. Sea temperature increases and coral stress from other impacts increase corals' vulnerability to bleaching. In 2015, the northern section of the Great Barrier Reef experienced large scale bleaching; a stress response to higher than average water temperatures. Previous mass bleaching events have shown that significant coral recovery can occur even from severe bleaching events. Whilst a significant portion of the coral may actually die as a result of the bleaching, the corals that survive will be more tolerant of high temperatures in the future.

Climate change is predicted to have far-reaching consequences for the reef ecosystem and over the next 50 years, it is likely to significantly affect most components.

More information:

• Great Barrier Reef Outlook Report

• Previous Pressures affecting marine ecosystems
• Next Coastal development pressure on the Great Barrier Reef