Sea level rise

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.

These are attributable to variations in the distribution of thermal expansion, local and regional meteorological effects, and 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.

Further information on sea level rise is available in a report prepared by the NSW Chief Scientist and Engineer.

NSW Government policy

As part of its 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 state-wide sea level rise projections for use by councils.

The 2009 NSW Sea Level Rise Policy Statement is no longer NSW Government policy.

The Office of Environment and Heritage has released guidelines on incorporating sea level rise into flood risk (10759FloodRiskManGde.pdf, 1.42MB) and coastal hazard assessment (10760CoastRiskManGde.pdf, 1.78MB).

These documents will be revised as part of the 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 twentieth 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. 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

The Intergovernmental Panel on Climate Change (IPCC) has developed a range of sea level rise projections, with the lowest projection effectively being a continuation of the current rate of observed sea level rise.

Further information on sea level rise projections is available from:

Additional information will be provided on sea level rise projections on this webpage.

Page last updated: 25 March 2013