Climate change and Australia’s coasts
Climate change is affecting our coasts via sea level rise and more energetic storms. The sea level is constantly fluctuating due to tides. An overall average is calculated using tide gauges and satellite measurements. Both methods of measurement show an increase in sea level over time. Approximately 45% of the rise in sea level is caused by the thermal expansion of water. Warm water is less dense than cold water, so takes up more space.
The other big contributor to sea level rise is the melting of glaciers and ice caps, accounting for 40% of recent sea level rise. Contributions from the ice sheets of Greenland and Antarctica make up the rest of the rise. Water stored on land and in the ground slightly offsets the rises, but sea level is increasing by 3 mm per year this century. This is nearly double the rate of last century.
The Australian Government estimates that sea level will rise by 1.1 metres this century. A rise of 0.5 metres by 2050 would mean that events happening every 10 years now will happen every 10 days. Important coastal facilities, like the airports in Sydney and Brisbane, are likely to be inundated as sea level rises.
Rising sea level threatens important infrastructure like the Sydney airport and Port Botany. (M Kozlenko 2015, Creative Commons)
Storm surge and coastal flooding
Climate change has added heat energy to global systems. On average, this means that storms now have more energy than they did in the past. Storm surge and storm tides are becoming more common. Storm surge occurs when low pressure and winds raise the sea level due to a storm. When high tide occurs at the same time as a storm surge, a storm tide causes even more massive sea level rise, often causing coastal flooding. Storm surge and tide are usually associated with East Coast Lows and cyclones.
Storm surge in Surfers Paradise. (B
Miller 2009, CSIRO ScienceImage)
Around 63% of the Australian coast is sandy or muddy. This is important because these soft sediments are vulnerable to erosion. Structures built in areas that were sand dunes are particularly vulnerable.
An example of this can be seen at Wamberal, north of Sydney. A number of houses were built on dunes that separate Terrigal Lagoon from Wamberal Beach. Several houses were lost to storm erosion in 1974 and 1978. In 2017, a state government study looked at the feasibility of building a seawall to protect the houses. The study concluded that without a wall all properties would be affected by coastal processes in 20 years and that sea level rise would accelerate this. Construction of a seawall would lead to loss of sand on a popular public beach, not protect against sea level effects and benefit only the owners of the houses.
Storms in July 2020 caused severe coastal erosion and several Wamberal houses were deemed unsafe due to loss of foundations. The effects of storm erosion can be seen in drone footage taken after one of the two storms that affected the area. The local council has been criticised for allowing construction in the area after the storms in the 1970s. New developments are unlikely to be approved after the 2020 events. Homes in coastal areas at risk are not insured for damage caused by the ocean, as this is so common and a foreseeable consequence of building near the shore.
Coastal erosion at Wamberal beach in 1978. (from AusGeo News March 2011)
Impact on coastal ecosystems
Governments and insurance companies can calculate the cost of rising sea level on structures and economies, but it is more difficult to put a value on coastal ecosystems. Climate change has many effects on ecosystems:
- Increased temperatures on land and in the ocean shifts the ranges of both marine and land animals.
- Sea level rise changes the salinity of estuaries.
- Greater water depth over coral reefs reduces their protection of coastlines.
- Light levels are lower at greater water depth, making it difficult for large algae and seagrasses to grow.
- More intense storms result in more sediment in runoff which may damage vital ecosystems, like mangrove fish nurseries.
- Breeding areas for penguins, seabirds, seals and turtles become smaller due to rising sea level and animals are stressed by increased heat.
Coastal ecosystems are important to humans. Mangroves are not only nurseries for baby fish, they also sequester carbon 40 times faster than forests. Damaging these ‘blue carbon’ ecosystems can release tonnes of ancient carbon stores back into the atmosphere. We may not have a dollar value for the natural areas of Australia’s coastlines, but this does not diminish their importance.
This mangrove seedling in Cairns is a vital part of the ‘blue carbon’ coastal ecosystem that sequesters carbon 40 times faster than a terrestrial forest. (G Blanchard 2003, Creative Commons)
Explore the effects of climate change on our coasts:
- Experiment with different ways to prevent soil erosion. Do you think these apply to coastal areas?
- Observe the effect of waves on a beach and see how this is changed by rising sea level (video).
- Learn about ocean acidification in this blog post and try the experiment shown in the video.
- Behind the News explains coastal erosion (video) and some of the ways we can try to prevent it.
- The Climate Council presents a detailed analysis of climate change and coastal flooding.
- Geoscience Australia explains the impact of climate change on our coastlines.
- CoastAdapt details the impacts of climate change on coastal ecosystems.