Wednesday, April 22, 2015

That Australian life - NSW storms with a dash of sea level history

The big storm that battered the NSW coastal strip from the Mid North Coast to the Illawarra appears to be coming to an end. The worst effects were concentrated in the Hunter Valley where five people died.

This photo by Dallas Kilponen from the Sydney Morning Herald shows the waves hitting Wylies Baths (the baths themselves are under water) at the Sydney beach side suburb of Coogee.
The waves were quite something. On Tuesday, a monster wave with a maximum height of 14.9 metres was recorded at 3pm, eclipsing the previous high of 14.1 metres set during the 2007 east coast low that washed the Pasha Bulker commodity carrier ashore near Newcastle. I wrote a post on that east coast low (New England's Wild Weather), in part because it came after drought, in part because of its scale. If you click on the link, you will see a photo of the Pasha Bulker that gives you an idea of then wave scale.

In an earlier post (New England prehistory: creating synthesis in the face of destruction), I mentioned that my present historical research was focused on prehistoric New England. My best guess is that the Aborigines came to Northern NSW between 30,000 and 40,000 years ago, although the earliest radio carbon dates are c20,000 years ago. As part of the process, I have been trying to map dates against changing sea levels and climatic variations.

Let me give you a number here just to attract your attention. Over the last 100,000 years, sea levels have fluctuated from perhaps 120 metres below current levels to a metre above.I was thinking of this as I listened to the storm reports. This variation was most pronounced over the last twenty thousand years.

I don't want to get into the now almost theological debate on human induced climate change. However, I am interested in sea level trends. During the Holocene Warm Maximum period that began c9,000 years ago, average temperatures were around half a degree hotter than they are now, the sea was a metre higher than now. That warm maximum period was replaced by a colder phase that saw sea levels fall.

We may or may not have entered a warmer phase now. Its interesting, however, to realise the scale of natural changes regardless of cause.   

Postscript

kvd, I mentioned John Mulvaney in a comment. This video may be of interest. Professor Mulvaney was mentor to Isabel McBryde who I think of as my personal mentor or role model in some of these areas:

7 comments:

marcellous said...

Funnily enough I heard someone making the same point the other night in the course of what turned out (to my mind) to be a kind of trolling argument - not that I am saying you are doing that.

It started with a denial of man-made global warming, then moved to a trope that "how can humans control the planet" then on to arguments that man made global warming was insignificant and attempts to prevent it pointless in the face of the much larger changes which had and could occur naturally.

The main point to me is that other than possibly the most catastrophic events, such as (is it the Devonian?) die back of many life forms possibly as the result of a meteorite strike, the natural changes have occurred at a geological scale of time. To think about let alone to prevent such changes does seem positively Ozymandian. But the changes which are occurring now are at a much faster pace. They have the potential to be highly disruptive and hence destructive of whatever fragile semi-status-quo underpins human society and the biosphere we have grown accustomed to.

That will be history whereas the bigger changes you have discussed might more aptly be called geology.

This is an issue that any intergenerational document such as that presently being touted Dr K on behalf of the government at present surely needs to address.

Jim Belshaw said...

The speed of these events at tip points should not be underestimated, Marcellous. If you were living on the flat plans of Northern Sahul and losing a metre of land to sea a year you would not think it a slow process. If you were living in Greenland and missed the last boat out, you would not think the change slow so far as you were concerned.

Just focusing on seal levels rises and ignoring the arguments of the denialists as irrelevant, the questions that have to be addressed is sea level rising, what are the implications? Having answered these questions, the next question is what are the causes, what to do about it?

I find some of the denialist arguments very useful because in seeking to rebut they are actually extending our knowledge of the human past and posing new questions for the future. However, if as they argue, we are just in a long warming phase, how much should temperatures rise before we start to worry?

During the warm Holocene,a good period,temperatures appear to have been half a degree higher than now. What happens if they go two degrees higher?

We will have a first round answer, I think, about all this in twenty years or so.

Anonymous said...

During the Holocene Warm Maximum period that began c9,000 years ago, average temperatures were around half a degree hotter than they are now

- said Jim, and you almost repeated that in your comment above.

Like you, I'm not interested in waking up the 'climate debate' but I would appreciate a reference for this statement, if available. It just seems so 'remarkably precise'.

kvd

Jim Belshaw said...

Good morning, kvd. The source is John Mulvaney & Johan Kamminga, Prehistory of Australia, Allen & Unwin, 1999, p226. I have actually misquoted. They write: "Throughout mainland Australia mean annual temperatures were 0.5C to 3C higher than present."

You have actually highlighted an interesting method challenge for a general historian such as myself. In this case, I have taken the two J's plus Josephine Flood's book as a base for my climate change stuff. I have then tried to translate it into regional terms using other studies that set individual digs or themes into contexts.

I am not an expert on this stuff, although I understand a little about the evidential base. I am trying to tell a story, putting forward a synthesis that can then be challenged. Because I have focused on a specific more defined area, most people are much more generalised, I have to drill to levels of detail normally ignored.

This is a bit of a sidetrack, but it bears upon my current preoccupation, dates and date patterns, recognising the limitations of things like carbon dating. I see a pattern, it fits with the climate evidence, but it could be attacked on a date by date basis.

Ah well. Such is life!

2 tanners said...

"I find some of the denialist arguments very useful because in seeking to rebut they are actually extending our knowledge of the human past and posing new questions for the future."

I can't agree here Jim. Most denialists appear to cherry-pick results and shift baselines to prove the point to which they are already committed. I find the interesting questions like 'Where will we be in 50 years' of far more interest than assertions such as 'An ice age might be coming so any AGW (not that it significantly exists) is potentially a good thing.

Anonymous said...

So, that's now the go - is it? Those who used to be reasonably termed 'sceptics', are now 'denialists'?

Must say I'm really surprised by both Jim and 'tanners using that terminology. Minds made up; all good to go, sort of thing.

Most denialists appear to cherry-pick results and shift baselines to prove the point to which they are already committed

Irony is such a short word; but I can't deny it provokes much wry humour.

Anyway, thank you Jim for the addition to your post. He seems a sensible, thoughtful sort of scientist - in the best meaning of that term. And I'm much more comforted with "0.5-3C" than "Half a degree". It seems much more human, in at least recognising possible fallibility.

kvd

Jim Belshaw said...

I used the word denialist advisedly, kvd. A skeptic is someone different.

Let me give you a case in point that also illustrates why I find some of their historical arguments useful

After a web search, I downloaded a very useful piece on climate/sea level change over time. Towards the end, I suddenly said wait a minute for the argument was twisting, morphing into an attack on human induced climate change. At that point I switched off because I felt that the evidence was being twisted, misused.

2T, that's a bit of a parody! At this point, I don't think anybody knows where we will be in fifty years time. I also strongly object to the distortions introduced in public policy by the climate change fanatics.

Mind you, I have also argued that we may well know in ten years and have not objected to sensible measures taken on the precautionary principle. I just hate the Green moral police!