Sea level rise
Most people expect that sea levels will rise due to ice sheets and glaciers melting at the poles, and they are right. However, a significant component of rising sea levels (around 57 per cent since 1993) is due to thermal expansion of water. Thermal expansion describes how, as water warms, it has a greater volume than the same amount of cool water. Therefore sea level is expected to rise faster in warmer regions, such as the east coast of Australia.
One of the oldest sea level benchmarks in the southern hemisphere can be found in Tasmania, etched into the rocks on the Isle of the Dead, Port Arthur. The benchmark provided some of the first sea level records, taken by local storekeeper, (and clearly a budding scientist) T.J Lempriere and a visiting captain, James Ross.
It is amazing that such a simple action has enabled scientists to make accurate sea level rise calculations over 150 years later. One such scientist, Dr John Hunter, an oceanographer at the Antarctic Climate & Ecosystems Cooperative Research Centre has used this historical tide data to determine the relative sea level rise off the coast at Port Arthur.
By using the benchmark records and more recent information, from 1841 to 2002 (and taking into account land uplift) sea level rise due to increased ocean volume was calculated by Dr Hunter to have increased 1.0±0.3mm/year or approximately 17cm at Port Arthur
Dr John Hunter, ocenographer.
Modern techniques used to gather sea level data include permanent tidal gauges (Permanent Service for Mean Sea Level PSMSL) and satellite altimeters. Satellite altimeters measure heights, and in the case of sea level the altimeters measure a radar pulse from the satellite to the sea surface and back again. They provide the most recent sea level data, only being in operation since 1992.
In Australia the National Tide Centre (NTC) has 14 permanent tidal gauges or SEAFRAME (SEA-Level Fine Resolution Acoustic Measuring Equipment) stations across Australia (as seen below). These gauges are sensitive enough to measure the small and gradual changes which scientists predict are occurring as a result of global warming. Every hour sea level data is collected by the NTC and summarised in monthly reports for the Australian Baseline Sea Level Monitoring Project.
In Tasmania sea level is monitored by tidal gauges at seven locations: Georgetown, Spring Bay (Triabunna), Hobart, Granville Harbour, Stanley, Burnie and Devonport.
Projected Sea Level Rise
While there are some discrepancies between the available data pertaining to the amount of sea level rise in the 20th century there is greater uncertainty when projecting future sea level rise. This is because the consequence of large scale melting polar caps, glacier and icesheets is considerable, and yet relatively unknown, thus resulting in much debate and speculation about the projected sea level rise related to how much melt will enter the ocean.
The Intergovernmental Panel on Climate Change (IPCC) states projections of global sea level rise show an increase in sea levels, relative to 1990 levels of between 18 and 59 cm by 2095. However there is provision for larger values should there be increased ice melt from Greenland and Antarctica which increase the projections by a further 10 to 20 cm.
Increased sea levels will greatly impact upon low lying regions including islands, beaches and wetlands. A rough guide suggests that, as a rule of thumb, a 1 cm rise in sea level could result in the loss of 1 meter of beach.
Want to know more about sea level rise and our oceans? Check out these links:
The National Tidal Centre (NTC) website with reports of sea level readings from tidal gauge facilities across Australia
The CSIRO Sea Level Rise website
Source:
Redmap would like to thank John Hunter for his considerable contribution to the sea level section. His assistance has been greatly appreciated.
Climate Change and Australia’s coast communities CSIRO Department of Climate change web site
Church, J.A., J.R. Hunter, K.L. McInnes and N.J. White (2006), sea level rise around the Australian coastline and the changing frequency of extreme sea level events. Australian Meteorological Magazine, 55, 253-260
Hunter, J.,R. Coleman, and D. Pugh, The Sea Level at Port Arthur, Tasmania, from 1841 to the Present, Geophys. Res. Lett., 30(7), 1401, doi:10.1029/2002GL016813, 2003.
IPCC (2007) Climate change 2007: impacts, adaptation, and vulnerability. Working group II contribution to the intergovernmental panel on climate change fourth assessment report. IPCC Secretariat, Geneva.
Sharples, C., 2006: Indicative Mapping of Tasmanian Coastal Vulnerability to Climate Change and Sea-Level Rise: Explanatory Report (Second Edition); Consultant Report to Department of Primary Industries & Water.
Tasmanian shoreline monitoring and archiving project (TASMARC)
The National Tidal Centre (NTC)
