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Sea Level Rise Around Mainland Australia

Reference
Watson, P.J. 2011. Is there evidence yet of acceleration in mean sea level rise around mainland Australia? Journal of Coastal Research 27: 368-377.
Watson (2011) writes that "Australia has become a coastal society," noting that "around 85% of the population live within 50 km of the coast," and he says that "the Australian coastal zone has been developed with the expectation that the shoreline will remain stable ... and that mean sea level will not change (Australian Government, 2009)." Hence, it is important to see what long-term tide gauge records suggest in this regard.

Working with average monthly water level data from the four longest, continuous Australasian records available -- those of Fremantle, Western Australia (January 1897-present), Auckland Harbor, New Zealand (November 1903-present), Fort Denison, Sydney Harbor, New South Wales (June 1914-present) and Pilot Station, Newcastle, New South Wales (April 1925-present) -- Watson converted them to relative 20-year moving-average water-level time-series and fitted them to second-order polynomial functions to look for trends that may have developed over the years.

The Principal Coastal Specialist of the New South Wales Department of Environment, Climate Change and Water reports, first of all, that the relative water level record of Newcastle is partly contaminated; but he indicates that "the longest continuous Australasian records, Fremantle and Auckland, situated on the western and eastern periphery of the Oceania region, respectively, exhibit remarkably similar trends in the relative 20-year moving average water level time series after 1920," with both time series showing "a rise in mean sea level of approximately 120 mm between 1920 and 2000 with strong correlation (R2 >= 0.93) to fitted second-order polynomial trendlines that reflect a tendency toward a general slowing in the rise of mean sea level (or deceleration) over time on the order of 0.02-0.04 mm/year/year." And he adds that "the Fort Denison water level time series after 1940 similarly reflects a decelerating trend in sea level rise at a rate of 0.04 mm/year/year based on a strongly correlated fit (R2 = 0.974) to the second-order polynomial function."

On shorter timescales, Watson notes "there is a high rate of relative sea level rise averaged over the decade centered around 1994," but he says that this recent acceleration is "not remarkable or unusual in the context of the historical record available for each site over the course of the 20th century," and he states that "these recent post-1990s short-term accelerations fit within the overall longer term trend of deceleration evident in the long Australasian ocean level records."

Although the four data sets employed in this study all show short-term accelerations in sea level rise near the end of the 20th century, the century as a whole was one of decelerating sea level rise, which is not exactly in harmony with the climate-alarmist contention that the 20th century experienced a warming that rose at a rate and to a height that were both unprecedented over the past millennium or more. However, the Australasian records do harmonize with those of the United States -- and much of the rest of the world -- as demonstrated by the recent analysis of Houston and Dean (2011), where slight decelerations also rule the century.

Additional References
Australian Government. 2009. Climate Change Risks to Australia's Coast -- A First Pass National Assessment. Australian Department of Climate Change, Canberra, Australia.

Houston, J.R. and Dean, R.G. 2011. Sea-level acceleration based on U.S. tide gauges and extensions of previous global-gauge analyses. Journal of Coastal Research (in press).

Archived 12 April 2011