Rising seas or sinking islands?

28 May 2003

Measuring tide heights is only part of the picture in sea level monitoring. Tide gauges measure sea levels relative to the land - but what if it's the land that's moving and not the sea?

At only a few metres above sea level, many South Pacific islands are at great risk from potential sea level rises due to global warming. In Fiji recently, Geoscience Australia met with other participating Australian organisations (National Tidal Facility, CSIRO, AMSAT and AusAid) and representatives of the Pacific Island Countries counterpart agencies, to report on the status and future directions of the South Pacific Sea Level and Climate Monitoring Project.

As part of the third phase of the project, Geoscience Australia is establishing a Continuous Global Positioning System (CGPS) network near sea level monitoring stations in the South Pacific region.

This network is used to accurately measure vertical and horizontal movement in the land. When this information is analysed together with tide gauge data it will assist in determining absolute sea level variation.

"If the land moves, say due to tectonic shifts or land subsidence, shifts as small as a millimetre will be detected by the CGPS system, allowing sea level observations to be adjusted to account for this movement," said Geoscience Australia's Dr Ramesh Govind. "Gaining this level of accuracy is crucial as sea level changes of around 1mm to 2 mm per year are being recorded around the world."

Dr Govind, who reported on the status of the network at the meeting, says that achieving this high level of accuracy will take at least a decade of continuous monitoring, but that already a lot of data has been collected.

"We currently have nine CGPS stations installed across the Pacific Islands, and several more to be installed later this year. The first was installed in Samoa in June 2001 and the latest in the Federated States of Micronesia at the beginning of May this year", he said. "That means we have nearly two years of data from Samoa."

By processing the information already gained from Samoa and other stations Geoscience Australia will assist in the management of marine environments and coastal zones affected by sea level rise in the South Pacific.

Topic contact: media@ga.gov.au Last updated: October 4, 2013