UPDATED 30 JULY 2016 TO INCLUDE DATA FOR 2014 AND 2015.
Sea levels in Sydney have been recorded since 1886 on a small island, Fort Denison, in Sydney harbour.
There have been two gauges used at Fort Denison; 1886-1993 and 1914-present. A comparison of the two records shows a close correlation and therefore the average values were adopted for the overlapping period. The combined record spans a period of 130 years from 1886 to 2015. The monthly data were compiled by PSMSL (Permanent Service for Mean Sea Level), the global data bank for long-term sea level data. The latest data used was for December 2015. The sea level data used were relative to Fort Denison island, with no adjustments being made for estimated long-term uplift or settlement of the island.
The plot of the annual mean sea levels indicates that the annual mean sea level (MSL) was virtually stationary or falling slightly (about 1 cm) between 1886 and 1949, but since then has risen by about 5 cm. A linear correlation of annual MSLs between 1886 and 2015 has a gradient of 7.1 cm/century.
A plot of the 5-year mean MSLs smooths out the annual variations. It is not clear from the plots if there has been change in the rate of sea level rise around 1950 or whether the data is part of a cyclical pattern with a trough around 1930 and a peak around 2010.
It is interesting to note that the annual MSLs exhibit short-term cycles with periods of about 20 years. There are seven distinct period when there has been a sudden steep increase in MSL over a period of up to 10 years, followed by a sudden decrease in MSL over a similar period. 10-year or more periods of rising MSL were experienced in 1902-1911, 1947-1956 and 2004-2015. During these periods the short-term rate of MSL rise can be 10 or more times the long-term mean rate. This clearly demonstrates the danger of considering only short periods of records (say less than 50 years).
Within each year there is also a seasonal variation in MSL with the average value in May and June being about 8 cm higher than that in the spring and summer period.
- The Sydney sea level records are a valuable data source for assessing sea level changes in south-eastern Australia.
- The long-term rate of sea level rise in Sydney of 7.1 cm/century (or 0.7 mm/year), a very low rate which is barely noticeable by local residents or infrastructure.
- The short-term steep rises in sea level are of particular interest and demonstrate the danger of using short periods of data to formulate long-term planning.