It’s hard to measure sea levels, because land often moves up and down too (which is known as “isostatic“). But Australia is stable tectonically, so the Australian sea-level record is more useful than most. It preserves the holocene era and the rises and falls, and correspond more with glacio-eustatic (ice equivalent) sea-level changes, rather than changes in land masses.
During the coldest days of the last ice age (known as a glacial maximum) 20,000 years ago, the oceans were 125m lower than today. They peaked at around 1 -2 meters higher than present between 9000 and 5000 years ago, and have been trending down ever since. Our current rate of 30cm/century (if that continues) hardly seems unprecedented or highly unusual. And 10% of that is apparently due to an isostatic “adjustment”. Worse, if you look at the raw data, the rate is closer to zero. Hmm. Lucky we have all those adjustments eh?
If Australian sea levels keep falling at this rate, we might really need to save That Reef.
Clearly there are many details yet to be worked out about sea-levels.
That phenomenal rise out of the ice age:
WA and NSW coastlines are considered the most stable
“Bryant (1992) reviewed the variable sea-level highstands of the last interglacial (based on the analysis of Murray-Wallace and Belperio, 1991) and mid-Holocene around Australia and found that there was possible downwarping of northern Australia and up warping along the southern edge of the continent (including Tasmania). Most of the east coast of New South Wales and west coast of Western Australia were classed as relatively stable.
Although most parts of the Australian continent reveals a high degree of tectonic stability, research conducted since the 1970s has shown that the timing and elevation of a Holocene highstand varies systematically around its margin.This is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice-melt, including a process known as ocean siphoning (i.e. glacio-hydro-isostatic adjustment processes).”
The holocene period in NSW
A steady decline in sea levels in WA for 7000 years
The last 8000 years in Queensland
The reviewers call for empirical evidence of the past, so we can predict the future.
Fairbridge’s pioneering research led, not to a global eustatic curve as he had anticipated, but to the recognition that the pattern of relative sea-level change in the Australian region differed from that observed in the Atlantic. A series of seminal sea-level studies were undertaken in the following 25 years. The stabilisation of sea level close to its present elevation in the mid- Holocene set the scene for the detailed reconstructions that were undertaken at different locations around the Australian mainland.
A clearer understanding of past sea-level changes and their causes is urgently needed to better inform our ability to forecast future changes. A concerted effort is required, through the compilation of existing data, renewed fieldwork, dating analysis and modelling to address the issues of whether there have been oscillations of the sea surface and if so, of what magnitude.”
Lewis, S.E., et al., Post-glacial sea-level changes around the Australian margin: a review, Quaternary Science
Reviews (2012), http://dx.doi.org/10.1016/j.quascirev.2012.09.006 [abstract] (paywalled).
Other posts on sea levels
- Man-made sea-level rises are due to global adjustments
- Councils become climate experts too. (Now Big-government insanity comes from small councils)
- Australian sea level rises exaggerated by 8 fold (or maybe ten)
- It wasn’t CO2: Global sea levels started rising before 1800
- 10% of sea level rise is due to land rising too. Got that?