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Climate Variability and Change (continued)

Sea level change [A Indicator 1.3]

Tide-gauge data show that global average sea level rose between 10 and 20 cm during the 20th century (IPCC 2001), while mean sea level around Australia rose by about 12 to 16 cm during the 1900s (Lambeck 2001). This value is consistent with the IPCC (2001) global estimates, but contains substantial regional variations. IPCC (2001) projects an increase in sea level of 9 to 88 cm by 2100.

Sea level changes are calculated from data gathered from tide gauges installed along the coastline of Australia for port operations. Records from several stations have been collated by the National Tidal Facility (Figure 39). Several records are affected by very local processes, such as subsidence, that reflect changes in local land level rather than sea level. All gauge heights are also affected by slower geological processes, whose contribution can be estimated using various techniques. Stations that are considered reliable include Fort Denison and Fremantle. After correction for geological effects, data from these two stations suggest a sea level rise of 12 to 16 cm during the last 100 years (Lambeck 2001).

Furthermore, a strong positive correlation has been found between year-to-year variations of sea level around Australia and ENSO (correlation between the first mode of sea level variations and the SOI is 0.8 based upon the last 30 years of data). The effect of ENSO on sea level is small in some locations, however.

Tide gauge records at specific locations may be affected by local subsidence and geological processes. Many locations around Australia have data for more than 30 years (Figure 38). Researchers believe that at least 30 years of good quality data are required to estimate trends from tide records. Some locations such as Fremantle have about 100 years of data, Port Denison has data for 85 years and Port Adelaide Inner and Outer Harbour have more than 50 years of data. Fremantle shows an increase in sea level of 1.38 mm/year. Port Adelaide Inner and Outer harbours show an increase of 2.06 and 2.08 mm/year, although these two records are likely to have been affected by local subsidence (Lambeck 2001). In contrast, several stations have shown decreases in sea level (e.g. Port Hedland shows a decrease of 1.32 mm/year).

Implications

The strong link between ENSO and sea level on the interannual time scale suggests that changes to ENSO behaviour under climate change conditions may affect the coastal community and urban infrastructure in some locations. Significant changes in global average sea level would have strong implications for the sustainable development of planned infrastructure including coastal development, ports, bridges and urban centres, and coastal ecosystem management. Continued monitoring of sea level around Australia and in the Pacific is essential for future estimates of sea level rise and ENSO-related effects on Australia.

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