Climate change impacts on islands and cays

Islands may be affected by rising sea levels that will inundate low-lying areas and higher air temperatures. Changes in rainfall and increasing storm activity may affect island plants and animals.

Islands and cays are important for many species, particularly marine turtles and seabirds that nest on their beaches, and plants and animals evolved to live on islands. They provide critical habitat for a number of protected species and are a unique component of the Great Barrier Reef seascape. 

Sea level rise

The impacts of sea level rise on islands and cays are not straightforward. Whether low-lying islands are likely to be inundated over time, or whether they will grow to keep pace with rising sea levels (at least in the short-term) depends on a number of factors.

For example, coral cays are built from a continuous accumulation of sand fetched across a reef by wave action. Whether the cay can continue to grow depends on there being an ongoing source of sand and coral rubble.

Scientists predict that the sea level rise over the course of this century may actually lead to an increase in the size and number of coral cays on the Great Barrier Reef in the short-term. With a rise of around one metre, most low-lying islands and cays are likely to be inundated.

In the early stages of this process sea level rise is likely to cause problems for plants and animals, such as inundation of breeding and nesting sites, and seawater intrusion into fresh groundwater sources.

Rising air and sea temperatures

Rising air and sea temperatures and regional changes in rainfall may also affect island habitats. For instance, warmer air temperatures increase the risk of fire, especially if there is an increase in the number of very hot days.

The types of plants living on islands are likely to change over time. Warmer temperatures are likely to favour drought- and fire-adapted plants, although this will depend on changes to rainfall. In a warmer climate, certain diseases, and many weeds (e.g. lantana) appear to be at an advantage.

Animals will be affected as well. For example, higher sand temperatures can alter the sex ratio of turtle hatchlings (see marine reptiles). The isolation of many Great Barrier Reef islands may also inhibit the natural southward migration of animals and plants as temperatures rise.

Changing rainfall patterns

Regional changes to rainfall patterns will play an important role in determining how island habitats respond to climate change. Increased or decreased rainfall, or changes to the timing of rainfall, would greatly alter the fire risk on islands. Some animal and plant communities on islands and cays will degrade over time. Specific changes will depend on the combined effects of changing rainfall, drought and fire regimes resulting from climate change.