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Sea level rise

Global sea level rise

There is a significant body of evidence that suggests the increase of ‘greenhouse' (heat-absorbing) gases in the atmosphere has resulted in a warming of the global climate during the previous century. Predictive work indicates that this warming will accelerate in the future due to continued anthropogenic greenhouse gas emissions. In the 20th century global average sea level has risen by 10-20 cm, primarily due to global warming. This sea level rise will continue, and possibly accelerate, over the next century and beyond, through a combination of mechanisms including:

• thermal expansion of the oceans;
• melting of glaciers and ice caps;
• melting of the Greenland and Antarctic ice sheets; and
• changes in terrestrial storage.

Regional variation in sea level rise

Factors that can cause regional variations in sea level include [2]:

• geological effects caused by the slow rebound of land that was covered by ice during the last Ice Age (‘isostatic rebound');
• flooding of continental shelves since the end of the last Ice Age, which pushes down the shelves and causes the continent to push upwards in response (‘hydroisostasy');
• changes in land height in tectonically or volcanically active regions;
• changes in atmospheric wind patterns and ocean currents; and
• local subsidence due to sediment compaction or groundwater extraction.

Issues arising from sea level rise

Changes in sea level will be felt through [1]:

• increases in intensity and frequency of storm surges and coastal flooding;
• increased salinity of rivers, bays and coastal aquifers resulting from saline intrusion;
• increased coastal erosion;
• loss of important mangroves and other wetlands (the exact response will depend on the balance between sedimentation and sea level change [2]); and
• impact on marine ecosystems i.e. coral reefs.

Any or all of these changes may have a severe impact on urban communities if unmitigated.

Useful links

• CSIRO: Sea Level Rise;
• National Tidal Centre of Australia;
• Intergovernmental Panel on Cllimate Change (IPCC);
• The University of NSW Connected Waters website: Coastal aquifers.

References

1. Scavia, D., Field, J.C., Boesch, D.F., Buddemeier, R.W., Burkett, V., Cayan, D.R., Fogarty, M., Harwell, M.A., Howarth, R.W., Mason, C., Reed, D.J., Royer, T.C., Sallenger, A.H., and J.G. Titus. 2002. Climate change impacts on U.S. coastal and marine ecosystems. Estuaries 25(2), 149-164.
2. Woodroffe, C.D. 1995. Response of tide-dominated mangrove shorelines in northern Australia to anticipated sea-level rise. Earth Surface Processes and Landforms 20, 65-85.