Indicator: CO-03 Sea level

Data

Trends in relative sea level have been derived for 32 Australian long-term sea level records that are archived at the National Tidal Centre (NTC). The datasets are hourly sea levels with respect to the tide gauge zero, which is tied to the primary tide gauge benchmark at each site.

Rise in sea level summary
Years of Data Trend (mm/yr)
Average (all stations) 39.6 0.9
Average (excluding Point Lonsdale, Burnie and Melville Bay) 40.3 1.2

Source: Bureau of Meteorology 2003, National Tidal Centre: Australian Mean Sea Level Survey, viewed 8 Jun 2006, http://www.bom.gov.au/oceanography/

What the data mean

The sea level data are analysed for tides and seasonal cycles in addition to the linear trend. The trend estimate will change as new data are accumulated. The minimum length of sea level record used in this survey is 25 years, which provides a reasonable initial estimate of the underlying long-term sea level trend, aside from the effects of normal sea level fluctuations associated with variations in climate, such as El Niño - Southern Oscillation and Pacific Decadal Oscillation.

The observed trend in relative sea level will also include the effect of any vertical land movement at the tide gauge site. This must be taken into account in order to estimate absolute sea level rise.

The trend estimates for each of the long-term relative sea level records show sea levels to be rising in the range of about 0 - 2 mm/yr and are distributed reasonably uniformly around the Australian coastline. The overall average relative sea level trend for all 32 long-term stations around Australia to December 2003 is a rise of 0.9 mm/yr.

This is consistent with a global average sea level rise over the last 100 years of 1 - 2 mm/yr.

Data Limitations

The negative trends at Point Lonsdale (-1.57), Burnie (-1.59) and Melville Bay (-2.43) are notable outliers to the national average, suggesting substantial contamination due to unstable tide gauge data. Excluding these stations, the overall average relative sea level rise around Australia is 1.2 mm/yr.

Issues for which this is an indicator and why

Coasts and Oceans — Condition of the ocean and coastal waters - Climatic and carbon dioxide factors 

Sea level is an aspect of the condition of the ocean itself, as distinct from its biodiversity, although its potential impacts on both marine and coastal biodiversity are substantial. Rates and extent of sea level change are potentially affected by climate change.

Other indicators for this issue:

Coasts and Oceans — Contributions and pressures between the coasts and oceans and the atmosphere - Climate and carbon dioxide 

Sea level change may occur as a consequence of climate change and is therefore an indicator of pressures from the atmosphere, particularly from greenhouse gas concentrations, on the ocean.

Other indicators for this issue:

Coasts and Oceans — Contributions and pressures between the coasts and oceans and inland water - Effect of changes in coasts and oceans on inland waters 

Sea level change has potential impacts on the ecosystems at the interface of coastal and inland waters, as freshwater or brackish systems become more saline.

Other indicators for this issue:

Coasts and Oceans — Contributions and pressures between the coasts and oceans and land - Effects of changes in the ocean on the land 

Sea level change has the potential to place pressure on the land as coastal terrestrial ecosystems become drowned or saline. Invasion of the coast by the ocean also has the potential to impact on the ocean as marine organisms are exposed to acid sulphate soils.

Other indicators for this issue:

Land — Contributions and pressures between the land and the ocean - Pressures of ocean change on the land 

Sea level change has the potential to place pressure on the land as coastal terrestrial ecosystems become drowned or saline.

Other indicators for this issue:

Biodiversity — Pressures on biodiversity - Climate variability 

Changes in sea level are likely to result from changes in global climate and are therefore an indirect indicator for these changes.

Other indicators for this issue:

Atmosphere — Climate variability and change - Greenhouse 

Changes in sea level are indicative of melting polar ice and may therefore be indicative of anthropogenic climate change due to the emission of greenhouse gases and the loss of greenhouse sinks.

Other indicators for this issue: