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One of the greatest challenges of coastal land-use policy is predicting future rates of sea-level rise from different proposed climate change scenarios. This study uses evidence from past higher Holocene and Pleistocene shorelines in southern Australia to develop possible response functions for future sea level modelling. A rule-of-thumb is determined by comparing rising sea levels of the past from relic intertidal biological markers with Antarctic temperature fluctuations during the mid-Holocene. The result is that for every 1°C increase in Southern Hemisphere relative temperatures, there would be, on average, a 0.9-m positive response in mean relative sea levels. Spectral analysis, comparing mean sea-level records from Sydney, Australia; the Southern Hemisphere temperature anomaly data (1850 to 2011); and Antarctic temperature fluctuations from the last 7000 years suggest that there are significantly longer (~20 y and ~50 y) periodicities that must be accounted for in any accurate determination of projections for 2100. For southern Australia, past sea-level rise appears to be in phase with Antarctic temperature changes and possible meltwater surges, suggesting that the use of linear sea-level rates per year, whilst convenient for planning, may be physically misleading. The policy response from the past should be a precautionary principle, based on centennial envelopes, capturing possible intermittent rapid surges that can be punctuated by decadinal stillstands. Three past-present-future (PPF) sea-level scenarios are applied to a case study of an area surrounding the Hexham Swamp, Newcastle, Australia. An impact infrastructure audit is undertaken, using a light detection and ranging geographic information system relative to multiple PPF centennial sea-level rise envelopes, to plan in this context for future sea-level rise. |
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