Climate change and sea levels in the South Pacific Case Study Click on the following links for further information about this case study: Teacher's Notes Student Activities Background Scientists have warned that one of the likely consequences of the enhanced greenhouse effect is a rise in sea level. Estimates of the possible rise in sea level vary from 2 to 9 mm/year, however local climatic variations such as El Niņo (or La Niņa) cycles may result in larger short term changes in some regions. Islands in the South Pacific face a number of problems associated with sea level rise. Some islands, such as the atoll islands of Tuvalu, barely exceed 2-3 metres above sea level and are composed of highly mobile sediments. These islands are susceptible to wash-over during storms and shoreline erosion. They also have problems with the supply of potable water as they rely on low and unreliable rainfall or on shallow fresh groundwater cappings from lenses comprising mainly of seawater. Raised reef islands as seen in Niue are composed of hard limestone rock and their populated areas are at least 10 metres above sea level. The problem here is that their supply of fresh groundwater can be affected by variations in sea level. Small high islands with volcanic cores, typified by Rarotonga, appear less likely to be affected by sea level changes. However, most of their people live within one kilometre of the shore and mostly at less than three metres above sea level. These islands face the same problems as the atolls. Even the large, high islands face the same problems as much of their economic activity, infrastructure and settlements are in the coastal zone. The islands of the South Pacific are also exposed to other factors which can produce sea level changes. For example, they vary widely in their exposure to tropical cyclones and associated storm surges, and they may suffer the effect of tectonic and volcanic activity. As a result some islands are sinking and others are rising or tilting. The hazards associated with sea level changes and the limitations they place on development in these island countries need to be considered in the context of other problems these countries have. These include remoteness, limited land resources, population pressures and stress caused by waste disposal and pollution. Sea level monitoring project The South Pacific Sea Level and Climate Monitoring Project is an initiative to establish a regional network to monitor the sea level and the possible impact of climate change. The project was developed by Australia in response to concerns raised by the member countries of the South Pacific Forum on the potential impacts of the enhanced greenhouse effect on climate and sea levels in the region. The Project aims to help Pacific Island countries and their governments gain more detailed information on the scale and implications of changing sea levels and climate. The task is particularly difficult in the Pacific as climatic events or long-term climate change is only one part of the pattern of changing sea levels. As pointed out above, other factors affecting sea levels include earthquakes resulting from the movement of Earth's crust due to movements of continental plates and volcanic activity which all occur in the region. The Australian Government's overseas aid agency, the Australian Agency for International Development (AusAID), is responsible for administering the Project. In 1991, the National Tidal Facility (NTF) of Flinders University in South Australia was awarded the contract to manage and develop the Project. The first phase of the project from 1991 to 1995 saw the establishment of eleven monitoring stations across the southwest Pacific basin. Monitoring stations are located in the following countries: Cook Islands, Fiji, Kiribati, Marshall Islands, Nauru, Papua New Guinea, Samoa, Solomon Islands, Tonga, Tuvalu and Vanuatu. All stations were operational by October 1994. Although the Federated States of Micronesia (FSM) and Niue are member countries of the Forum, sea level and climate monitoring stations have not yet been established there as part of this Project. Recently, AusAID approved funding for a station in FSM. The project has continued and the next phase is being managed by AMSAT, while NTF will continue to monitor the gauges. Monitoring stations These stations use the SEAFRAME (Sea level Fine Resolution Acoustic Measuring Equipment) system which has also been installed around Australia (Figure 1). The equipment has built-in sensors that measure: water level, using a very sensitive acoustic sensor, and a pressure sensor as a backup wind speed and direction, and maximum wind gust; air and water temperatures atmospheric pressure. Figure 1 - A SEAFRAME monitoring station.   The equipment has the capacity to measure sea level changes within one millimetre accuracy, every six minutes. Other measurements are recorded once every hour. The sea level and climate data are regularly recorded and automatically transmitted via the Japanese Geo-stationary Meteorological Satellite and the telephone lines to the NTF in Adelaide, Australia. The Project produces monthly data reports which provide a summary of the data collected for the month with some discussion of the events affecting sea level and climate. These reports are available from the National Tidal Facility website at: http://www.ntf.flinders.edu.au/TEXT/ PRJS/PACIFIC/pacific.html Most of the monitoring stations also have a real time display (RTD) of the data which is available to the participating countries. This allows a computer close to the monitoring station to display the data being recorded by the SEAFRAME instruments. The RTD can also be accessed from the website at: http://www.ntf.flinders.edu.au/TEXT/ PRJS/PACIFIC/online.html Sea level trends Measurements of sea level show considerable variation over time. These are due to variations in tides, storm events such as cyclones, ocean events such as El Nino and catastrophic events such as volcanic eruptions and earthquakes. These variations are referred to as 'noise'. This noise makes it difficult to determine any long-term change in sea level. Figure 2 shows the apparent short-term sea level trends from the South Pacific stations since their establishment. This plot includes any natural variability such as El Niņo and effects due to many other atmospheric, oceanographic and geological processes. Initially these plots are very variable, but the extent of the variation reduces over time. For example, the positive trends at Papua New Guinea and the Solomon Islands are likely to decrease as sea levels drop when the next El Niņo phase is entered into. Figure 2 - Relative sea level trend analysis for the eleven SEAFRAME stations in the South Pacific based on data up to October 2000.   Examination of long-term records from other stations around the world suggests that a record of more than 20 years is required before any trend in sea level can be identified with certainty. Analysis of the data from monitoring stations around the Pacific with data records longer than 25 years produces an average increase in sea level of 0.8 mm per year. This result is on the low side of the estimate made by the Intergovernmental Panel on Climate Change (IPCC) in 1995 which suggests that the global trend is between 1 and 2 mm per year. However, it should be noted that this rate of change is about ten times more rapid than the average over the previous 3000 years as determined from the geological record. The South Pacific monitoring stations were only commissioned between 1992 and 1994, and so do not have the long-term records required for a complete trend analysis. Despite this limitation, it is still worth considering the current trends in sea level changes in the South Pacific. The data can give some indication of the possible cause of some local event such as crop loss or erosion. It is possible to determine whether this local event was due to a short-term natural event such as a tropical cyclone or whether it was due to long-term sea level changes. Table 1 shows the approximate changes in sea level at the sites of the South Pacific gauges between their establishment and January 2000. Table 1 Recent short-term sea level trends for the SEAFRAME stations up to October 2000. Location Number of months of record Sea level trend (mm/year) Change from previous month Fiji 96 +6.4 +0.4 Vanuatu 82 +6.6 +0.6 Tonga 92 +21.5 -0.4 Cook Islands 91 +6.1 -0.2 Samoa 91 -0.6 +0.1 Kiribati 89 -11.0 +0.5 Marshall Islands 84 +5.6 +1.2 Tuvalu 89 -5.0 +1.0 Nauru 85 -9.5 +0.6 Solomon Islands 71 (with gaps) +15.1 +0.9 Papua New Guinea 58 (with gaps) +21.2 +0.5 These values show that there have been significant sea level falls at Kiribati, Tuvalu and Nauru since the start of the project. The stations in Tonga, Solomon Islands and Papua New Guinea have shown a marked sea level rise. These larger changes in sea level are believed to be due to the recent El Niņo and La Niņa events, and the sea level changes will be reduced when the effects of these events subside.   Top © Commonwealth of Australia