ICSM Geodesy Technical Subcommittee Darwin 2nd September 2004 Bill Mitchell Manager

1. ICSM Geodesy Technical Subcommittee Darwin 2nd September 2004 Bill Mitchell Manager National Tidal Centre Bureau of Meteorology

3. Relative sea level trends (mm/year) for gauges with records longer than 20 years on the University of Hawaii Sea Level Centre archive +1.13 +0.37 +2.79 -0.2 +0.42 -0.68 +0.26 +0.64 +1.79 -2.24 -2.03 +0.89 -2.21 +1.43 +3.80 +3.99 Average relative sea level trend is +0.63 mm/year Regional coherency?

4. Instrumentation

6. South Pacific Sea Level and Climate Monitoring Project National Tidal Centre Bureau of Meteorology

7. National Tidal Centre Bureau of Meteorology

9. +5.9 +9.0 +4.7 +7.5 +6.8 +10.9 +5.5 +11.7 +13.4 +5.1 +6.3 +13.5 +5.4 +4.1 +1.4 +12.3 +4.0 +5.7 +10.3 +5.2 +7.4 +6.7 +3.2 +3.7 +3.9 Relative rates of sea level change (mm/year). All are positive with the highest rates in the Northwest of Australia National Tidal Centre Bureau of Meteorology

10. +0.3 +1.5 +0.6 +0.5 -0.1 +0.6 +0.5 +0.2 -0.4 +0.2 +1.7 +1.1 +0.9 +1.2 +0.1 +0.8 +0.7 +0.8 +0.9 +2.5 +1.2 +0.8 +0.2 +1.0 -0.2 Contribution of atmospheric pressure to relative sea level rise rates (mm/year) National Tidal Centre Bureau of Meteorology

11. +0.5 +0.2 -0.1 0.0 +0.4 0.0 +1.2 -0.3 -0.2 -0.9 0.0 Contribution of change of vertical datum to rate of sealevel rise (mm/year)

12. +5.1 +7.3 +4.2 +7.0 +6.5 +10.3 +5.0 +11.5 +13.8 +3.7 +4.9 +12.4 +4.5 +3.1 +2.2 +11.5 +3.3 +4.9 +9.4 +5.9 +2.7 +6.2 +3.0 +2.7 +4.1 Net rates of relative sea level rise (mm/year) as at 15th April 2004 National Tidal Centre Bureau of Meteorology

13. Sea Level and Climate Monitoring Project Conclusions On average, global relative mean sea levels have risen between 1 and 2 mm/year over the last century and there has not been a detectable acceleration in the last 50 years Rates of relative sea level rise may vary considerably between sites due to site specific influences such as meteorology, oceanography and vertical tide gauge movement and land motion The arrays are continuing to deliver long term, high quality datasets to the region and is thus satisfying their key objectives National Tidal Centre Bureau of Meteorology

14. Sea Level and Climate Monitoring Project Conclusions (continued) In order to derive stable estimates of relative sea level trends we must monitor for at least twenty years An integral component of the operation of a tide gauge is accurate surveying between the gauge and the benchmarks in the vicinity Changes in atmospheric pressure need to be monitored since they may significantly contribute to trends in sea level National Tidal Centre Bureau of Meteorology

15. South Pacific Sea Level and Climate Monitoring Project Conclusions (continued) Accurate monitoring of the geological motion of islands is necessary to adjust the trends - can use CGPS Note: beware of short-term datasets! National Tidal Centre Bureau of Meteorology

16. 86 years of tide gauge records at Fort Denison in Sydney Harbour show a trend of 0.9 mm/year and the monthly minima are rising faster than the monthly maxima

17. South Pacific Sea Level and Climate Monitoring Project Future Within three years a major refurbishment of the Australian Baseline Array Potential for installation of CGPS at each site as part of the refurbishment Will need to precise level between CGPS and Baseline station National Tidal Centre Bureau of Meteorology