Climate
Historical Changes in Sea Level
When looking at the present Tasmanian coastline it is important to understand that it is not static, and that it has changed its position, in a migratory pattern, over the recent geological times of the last 500 000 years. These migrations are mainly based around fluctuations in sea level, due to variations in the climate of the earth.
During colder climatic periods such as the ice ages, the polar ice caps expanded drawing in ocean water and ultimately lowering the level of the ocean. At such times Tasmania’s coastline was considerably lower than it is at present. This resulted in the coastline being situated offshore from its present day level.
During the interspersing warmer periods, the sea level rose and Tasmania’s coast retreated landwards. The present sea level was established about 6000 years ago, due to a period of sea level rise at the close of the last ice age.
Temperature changes predicted for 2050.
Source CSIRO Australia.
Sea-level rise over the last century is linked to global temperature increases responding to increases in greenhouse gases.
There are many components contributing to sea-level rise. These are:–
- Ocean warming and the resultant thermal expansion
- Widespread melting of non-polar glaciers
- Increased melting of ice in Greenland, partially offset by increased snowfall
- Increased snowfall over Antarctica (partially offsetting sea-level rise from other components)
- A long-term contribution from the Antarctic ice sheet, which is still responding to changes since the last glacial maximum
- Changes in terrestrial storages (for example aquifers and man-made dams).
It is important to realise that modification of coastal areas by physical processes may be interrupted at any time by a change in the relative position of sea level. The coastal zone will be flooded if sea level is relatively raised and hence termed submergent coasts.
The Department of Primary Industries and Water 
is coordinating Tasmanian Government efforts to address the issue of greenhouse gas emissions and climate change. Their website has links to a range of reports and information papers regarding climate change which are available for free downloading.
See also the website of the Bureau of Meteorology .
For more information on sea-level rise see the website of CSIRO Marine Research .
Current Climatic Influences
Map Showing Ocean Currents around Tasmania
(Source: Great Barrier Reef Marine Park Authority)
Tasmania has a temperate climate; however, the island can be affected by storms emanating from the polar regions at any time of the year.
Mean sea water temperatures range from around 10–12°C in winter (blue on the adjacent map) to around 18–20°C in summer (yellow, orange and red on the adjacent map), although the temperatures in sheltered or enclosed water bodies may fluctuate outside these upper and lower ranges.
The dominant climatic processes affecting the Tasmanian coast are successive high- and low-pressure systems in the zone of the Roaring Forties.
The storms resulting from these pressure fronts occur principally during winter, and are associated with predominantly south-westerly swells. Another important climatic process is the Southern Oscillation, which affects the ocean currents off the east coast.
Less frequently, subtropical low-pressure systems move down Australia’s eastern seaboard and bring storms and heavy seas to the east coast of Tasmania. Storms and swells affect the surface mixing of waters, water temperature, the supply of nutrients, the duration and intensity of sunlight at sea-level, and the clarity of the water. Tasmania’s tidal range is affected by both its location and latitude: the range is around 3–4 m in the Tamar estuary and less than 1 m in the south of the State.
Contact: Coastal and Marine Branch
Coastal and Marine Branch
6th Floor, Lands Building, 134 Macquarie Street
GPO Box 1751
Hobart TAS 7001
Phone: 03 6233 3963
Fax: 03 6233 6800
Email: Coastal.Enquiries@environment.tas.gov.au
