Sea level rise

Global sea levels are rising and increasing the risk to coastal communities from inundation and erosion.

The principal components contributing to global average sea level rise are the melting of land-based snow and ice reserves and the thermal expansion of the ocean water mass.

While global average sea level rise is relatively consistent, there are significant regional variations throughout the ocean basins of the world, which are attributable to:

  • variations in the distribution of thermal expansion
  • local and regional meteorological effects
  • regional responses to modes of climate variability (for example, the El Nino-Southern Oscillation).

There is also considerable short and long-term variability in sea levels at any particular location, with this variability often extending over multiple decades.

There are two related measures of sea rise:

  • absolute sea level rise, which is the increase in the ocean water level
  • relative sea level rise, which is the increase in sea level recorded on land and is affected by land movement at the tide gauge site.

NSW Government policy

Following a review by the NSW Chief Scientist and Engineer (PDF 1.6MB) and stage one coastal management reforms, the NSW Government announced that councils would have the flexibility to determine their own sea level rise projections to suit their local conditions. The Government would no longer prescribe statewide sea level rise projections for use by councils and the 2009 NSW Sea Level Rise Policy Statement would no longer be NSW Government policy.

The Office of Environment and Heritage has released guidelines on incorporating sea level rise into flood risk and coastal hazard assessment (PDF 1.8MB).

These documents will be revised as part of the coastal reform process. In the interim, reference to the NSW sea level rise planning benchmarks in these documents should be taken as referring to council's adopted sea level rise projections.

Recorded historical sea level rise

Recorded sea levels are influenced by factors such as tides, waves, storm surges, seasonal temperature effects, and longer term effects due to large-scale phenomena like the El Nino-Southern Oscillation. Therefore, short-term sea level records reflect short-term trends which may be different from long-term trends.

A 2011 analysis of global tide gauge records and satellite altimetry has found that:

  • Global average sea levels increased by 210 mm from 1880 to 2009.
  • While there was considerable variability in the rate of rise during the 20th century, there has been a statistically significant acceleration since 1900.
  • Between 1993 and 2009, the estimated rate of rise was 3.2 ± 0.4 mm per year from the satellite altimetry data and 2.8. ± 0.8 mm per year from tidal records. 

Longer term analysis of NSW data is available from tide records at Fort Denison based on relative sea level measurements (PDF 1.3MB). Equipment to measure the influence of land movement on tide records at Fort Denison was installed in May 2012 and will provide improved estimates of absolute sea level rise at this site over time.

Further information on observed historical mean sea levels is available from:

Projected future sea level rise

Increase in global mean sea level over the last century is thought to be associated with global warming as a result of increasing greenhouse gas concentrations in the atmosphere. The IPCC concludes it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century and future changes to climate are likely to depend on future greenhouse gas emissions.

In its fifth assessment report (2013), the IPCC has developed a range of future sea level rise projections associated with different greenhouse gas emission scenarios (representative concentration pathways (RCPs)). These indicate the following:

 

Scenario

Likely global mean sea level rise range by 2100

 (relative to 1986-2005)

Significantly Reduced Emissions (RCP 2.6) 0.28 - 0.61m
Highest Emissions (RCP 8.5) 0.52 - 0.98m

They also suggest the possiblity of up to several tens of centimetres above these values if marine-based sectors of the Antartic ice sheet collapse.

Beyond 2100, the IPCC concludes that it is virtually certan that global mean sea level will continue for many centuries due to thermal expansion of the oceans.

Data provided by the IPCC also indictes sea level rise along the east coast of Australia might be 0-10% above the global average by 2100 (relative to 1986-2005) with higher rates offshore.

Further information on sea level rise projections is available from:

Page last updated: 16 October 2014