Jennifer Marohasy

a forum for the discussion of issues concerning the natural environment

sea level change

King Tides at Cleveland Point, and Sea Level Change Over the Holocene

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ANOTHER year, and I’ve received another photograph from the Spangled Drongo, a regular commentator at this weblog who visits a waterfront property at Cleveland Point, Moreton Bay, Queensland, Australia, around this time of year.

Spangled is getting older, and back in the late 1940s and early 1950s he remembers the King Tides used to cover the law by about an inch or so.

This time last year, with the barometer reading normal, Spangled saw the King Tide was about 30cm below the lawn height and sent us a photograph, https://jennifermarohasy.com.dev.internet-thinking.com.au/2013/01/king-tide-not-so-high/

This year, according to Spangled, the highest astronomical tides were lower by around 20 cm and 10 cm respectively due to a small surge from the north. The first day of the King Tide, on January 2, Spangled says that the barometer was reading 1012 hPa and then yesterday (January 3) it was reading 1002 hPa.

Cleveland, January 3, 2014

Of course sea levels vary around a coastline depending not only on the tides, but also melting poles (climate change), land subsidence and vertical land motion (tectonic and isostatic phenomena). So around Britain the deglaciation of Scotland that occurred thousands of years ago means the northern part of that landmass is still adjusting and shows uplift (relative sea-level fall) while southern England shows subsidence (relative sea-level rise).[1]

Along the Australian east coast it is well document in the scientific literature that sea level was higher during the mid-Holocene around 6,000 years ago and have fallen in total about 2 m to more or less the present position over the last few thousand years. This is consistent with global climatic change over this period, in particular an overall trend of global cooling since the early Holocene.

So while the Bureau of Meteorology and CSIRO may nag on about a few centimeters of sea level rise over perhaps the last hundred years, the overall more significant trend during the present geological epoch, the Holocene, is one of sea level fall. The only real point of contention seems to be whether the fall has been smooth or oscillating over the last few thousand years.[2]

PS. I shall make some comment on the latest claims from the Bureau of Meteorology that 2013 was the hottest year ever in due course after I have had time to look properly at the data. In the meantime, my blog post from March is still very relevant https://jennifermarohasy.com.dev.internet-thinking.com.au/2013/03/cooking-books-for-hot-summers/

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References

1. This is all nicely explained in a paper by Ian Shennan et al. entitled Late Holocene vertical land motion and relative sea-level changes: lessons from the British Isles published in the Journal of Quarternary Science (volume 27, pages 64-70).

2. Lewis et al. published a controversial summary in Terra Nova (volume 20, pages 74-81) entitled Mid-late Holocene sea-level variability in eastern Australia.

Water Levels in the Swan River Estuary: A Personal Observation

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I READ with interest an article in The Fremantle Herald newspaper in which global warming was blamed for rising sea levels, which in turn were said to be submerging the mud flats in the Swan River estuary and thus destroying the habitat of migratory birds.

Reading it, I could not but reflect on my own observations of water levels and on the accretion and erosion of mud banks in the Swan River over my life-time. I have known the river intimately since the early 1940s when as a toddler I first paddled in the waters of Freshwater Bay. Over the years I have swum and fished in, and canoed, rowed and sailed on the river. I have cycled around the riverside paths, explored the river’s shores and bushland, walked my dogs at the river’s edge, and enjoyed the wildlife – some of which (like the river cobbler) seems to have disappeared, while other species (like the black swans) appear to be flourishing. I have known the river from Preston Point at East Fremantle to the Perth Causeway and beyond for over 60 years, and since 1980 I have swum regularly at the old Bicton Baths.

Over all this time I have seen the river rise and fall with the ocean tides, respond to flood waters coming down from the Avon, and fill to its brim with the run-off from heavy rain storms. But I have also seen the Point Walter sand spit so far above the water that it has grown a small-vegetated island. And only last summer there were occasions when the water was so low at Bicton Baths that the bottoms of the swimmers’ ladders were exposed and there were acres of temporarily exposed mudflats west of Alfred Cove and along the Como foreshore.

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King Tide Not So High

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Jen, Here is a photograph of the King Tide yesterday, 12th January 2013, at Cleveland Point, Moreton Bay.

The King Tides here, where I used to live from 1946 until the early 1950s, used to cover the lawn on this land by about an inch (25mm) or so. Today’s King Tide was 2.68 m at the Brisbane Bar (about as high as they get) and the barometer reading at high tide was 1012.5 hPa (normal).

There were no enhancing or diminishing factors influencing sea levels that I am aware of. The remaining decking on the ruined jetty (click on photograph to see more of jetty) is at the height of the top of the sea wall (lawn height) so it can be seen that the King Tide height is about 300 mm below the lawn height.

So, according to my observations, sea levels in Moreton Bay have gone down about 300 mm over the last 67 years.

Cheers, Spangled Drongo

Metres of Sea-Level Rise: Climate Commissioner

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WILL Steffen is the executive director of the Australian National University Climate Change Institute and also a member of the Australian Climate Commission. This is the Climate Commission established to provide all Australians with an independent and reliable source of information about the science of climate change. This is the same Professor Steffan who, you may remember, sort of fudged hot day data for western Sydney [1].

My name is Mr Koala and I’ve been reading the latest contribution from this professor who is paid to provide me with an independent and reliable source of information on climate change.

He has a piece in today’s national newspaper, The Australian. It’s really scary! Professor Steffan tell us:

“Scientists have painted a clear picture of the risks from failing to act on climate change. The natural world would experience the sixth great extinction event in Earth’s history, coral reefs would almost completely disappear, and we would be facing metres of sea-level rise as oceans continue to warm and polar ice sheets melt and disintegrate.”

Ouch. Nemo!

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Bad Moon Rising

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TIDES are a consequence of the gravitational attraction of the earth to both the moon and the sun with the moon generally being more than twice as strong as the sun because it is so much closer to the earth. The moon rotates around the earth with the lunar day approximately 50 minutes longer than then the mean solar day. When the sun and the moon are both pulling in the same direction higher tides, known as spring tides occur.   Really high spring tides are known as king tides.

Gradually the moon and the sun will fall out of step until their pulls are opposing resulting in neap tides.

The size of tides is not only affected by the direction of the gravitational pulls from the moon and the sun, but also their distance from the earth that changes because their orbits are elliptical. The astronomical phenomena while complex are predictable forming cycles that repeat with characteristics unique to each place on earth, tending to vary in predictable ways with topography and sea depth.

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Believing the Oceans Will Keep Warming

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ANTHROPOGENIC Global Warming (AGW) theory is currently the most fashionable climate theory and its proponents have risked much by predicting a continuation in what has been a 150-year general warming trend.

There are already some indications this trend is stalling with no increase in average global atmospheric temperatures for 15 years [1].

For those who subscribe to any one of the many theories that purport to explain natural climate variability the stakes are not so high: whichever way temperatures swing we can claim to be right. Indeed simply claiming that climate change is natural does not constitute a theory amenable to falsification.

There has been some arguing recently over ocean temperatures, in particular heat content, and how it is trending. I am happy to concede the AGW proponents might have one remaining residual warming trend to cling to here.

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