Climate change impacts on sea level rise

Key points

Sea levels are rising as a result of climate change. This rise is likely to accelerate over the coming century and continue for centuries.
The impacts of sea level rise include permanent flooding (inundation) of low-lying areas, and increased frequency, extent and depth of tidal inundation. Sea level rise will also cause most sandy beaches to recede (where beaches will move further inland) and erode.
Considerable development along the NSW coast is at risk from inundation and erosion as a result of sea level rise. Around 80% of the NSW population live within 50 km of the coast. The highest risk occurs close to estuaries, where a lot of development has occurred in low-lying areas.
All of these changes will damage our infrastructure, industries and coastal ecosystems, and affect our coastal communities.
Sea level rise is very likely to continue even if greenhouse gas emissions are reduced. For this reason, adaptation planning for ongoing coastal change is critical. This is being carried out through the NSW Coastal Management Framework, research, and raising community awareness of sea level rise impacts.

The impact of sea level rise in NSW

Sea level rise is projected to cause higher, more extensive and more frequent flooding (inundation) with very low-lying areas likely to be permanently inundated.

Climate change may also increase the severity of extreme weather events such as east coast lows. Sea level rise makes these events much more damaging, as the higher mean sea levels raise storm surge levels and increase erosion.

Sea level rise is likely to have very significant impacts on Australia’s people, environment, industry and economy.

Impacts on people

Sea level rise is a major threat for NSW.

Statewide exposure assessments show that while both erosion and inundation are major issues, the greatest concern in the long run is inundation around estuaries.

For example, regional scale modelling shows that

around 4800 lots (8200 total addresses) could be at least partially affected by erosion by 2100
up to around 74,700 properties around the foreshores of estuaries could be partially inundated during a major storm surge with 1m of sea level rise.

Exposure to sea level rise is highest around tidal lakes and close to the larger and more heavily populated coastal river systems. Within tidal lake systems, development has often occurred close to sea level. Much of this development has been shown to be only marginally above current high tide levels and is highly vulnerable to sea level rise.

In some estuarine areas, the number of days with some inundation of low-lying streets has more than doubled over the last few decades.

Erosion and inundation are likely to damage developments such as houses, roads and critical services like sewerage systems. Sea level rise will damage coastal areas which are important for cultural practices and social activities.

Impacts on industry and the economy

The areas likely to be affected by erosion and inundation include agriculture, commercial and light industrial buildings. Sea level rise will also have major impacts on existing and future coastal developments. Over the longer-term, losses in beach amenity will impact on local tourism - further impacting local economies.

Impacts on the environment

Sea level rise will result in changes to coastlines, tidal rivers and lagoons which will modify ecosystems – some of which are protected under international agreements. Sea level rise will cause erosion and flooding of important foreshore habitats, and affect water quality as salt water is pushed further upstream into freshwater ecosystems.

In intermittently closed and open lake and lagoons, increases in entrance berm height are likely to increase overall water levels, increase filling times and decrease breakout frequency. Some important foreshore habitats such as mangroves and saltmarsh may be able to adjust to low rates of sea level rise. Under higher rates of sea level rise space for these systems to migrate may need to be set aside if they are to continue.

Many coastal areas are important habitats for species that are critical to the food web, as well as the juveniles of many marine and land species. Damage to these habitats will therefore have major effects on our environment, and on associated industries.

Projected sea level rise along the NSW coast

There is a direct relationship between climate change and sea level rise. As our climate warms, sea level rises mainly because of thermal expansion (when water warms up, it expands) and melting of snow, glaciers and ice caps (which increases the volume of ocean water). However, sea level rise is also effected by local oceanographic processes (e.g. changes to ocean currents) and changes to land levels.

Sea level rise is projected to accelerate over the 21st century. The most recent sea level rise projections are from the Intergovernmental Panel on Climate Change (IPCC) 6th Assessment Report. The IPCC predict a likely sea level increase on the central NSW coast of

between 0.21m and 1.06m by 2100, and
between 0.28m and 1.95m by 2150.

This is dependent on the level of future greenhouse gas emissions.

IPCC modelling suggests slightly higher sea level rise to the north of the state and slightly lower to the south. These projections do not include processes associated with the melting of ice sheets which for NSW could result in sea level rise of up to 2.3m by 2100 and 5.5m by 2150.

In the longer term, the IPCC show sea level is committed to rise for centuries to millennia due to continuing deep ocean warming and ice sheet melt, and will remain elevated for thousands of years.

If warming is limited to 1.5°C, global mean sea level will rise by about 2 to 3m.
for 2°C, 2 to 6m is expected, and
for 5° 19 to 22m is expected.

Adapting to sea level rise in NSW

Governments, communities and individuals all play an important role in adapting to sea level rise.

The NSW framework for managing coastal hazards, including sea level rise, include:

Considering sea level rise when planning future developments is essential. For example, areas that are projected to be affected by sea level rise can be mapped as vulnerable areas where coastal hazards need to be considered before development being allowed and zoned appropriately in Local Environment Plans. NSW government resources include a toolkit with information and guidance for councils.

Adaptation of existing settlements will also be necessary. Options include actions such as raising houses and roads, installing tidal gates to restrict ingress of tidal water into stormwater systems, building levees and sea walls, and undertaking beach nourishment.

Maintaining healthy coastal ecosystems can reduce the impact that sea level rise has on surrounding areas. We can support coastal ecosystems to help maintain natural coastal defences. We can do this by:

maintaining or expanding coastal buffer zones
replanting and protecting coastal dunes
fencing creeks and rivers to keep livestock out
controlling invasive species
protecting and restoring mangroves and salt marsh areas.

Raising awareness of sea level rise impacts in coastal communities is an important part of adapting. Community education programs help people understand how sea level rise could impact them, and what is being done to manage it. People who are informed are more likely to support policies or projects which aim to manage the impacts of sea level rise.