Thursday, October 16, 2014

Sea levels and global ice volumes over the past 35,000 years

Sou | 5:06 PM Go to the first of 86 comments. Add a comment

Comments on this topic are closed. There is a new article on sea level where comments are welcome.

Sou 24 October 2014

Anthony Watts has seen fit to post a rather silly comment from Eric Worrall about a new PNAS paper on sea level and ice. Anthony also adds his tuppence-worth. (Archived here.)

The paper is from a team led by Professor Kurt Lambeck of The Australian National University (ANU).

A fascinating journey up and down the seas

What the Kurt Lambeck and his co-authors have done is paint a wonderfully vivid 35,000 year history of changes in sea level and major ice sheets.

It's taken me a while to read the paper. In part because the subject matter is provided in rich detail, and in part because I found it so fascinating. It's extraordinarily well written. The authors have managed to cram a huge amount of information into the few words allowed by PNAS, while writing in a manner that a lay person like myself could understand.

1,000 observations of sea level

The paper has a text box on the first page headed "Significance", which explains the value of the research to earth science of documenting changes in sea level going back 35,000 years. It also highlights their finding that, over the past 6,000 years and up until around 150 years ago, there was no evidence for global oscillations in sea level lasting longer than around 200 years or being larger than around 15 to 20 cm in amplitude. It states:
Several areas of earth science require knowledge of the fluctuations in sea level and ice volume through glacial cycles. These include understanding past ice sheets and providing boundary conditions for paleoclimate models, calibrating marine-sediment isotopic records, and providing the background signal for evaluating anthropogenic contributions to sea level. From ∼1,000 observations of sea level, allowing for isostatic and tectonic contributions, we have quantified the rise and fall in global ocean and ice volumes for the past 35,000 years. Of particular note is that during the ∼6,000 y up to the start of the recent rise ∼100−150 y ago, there is no evidence for global oscillations in sea level on time scales exceeding ∼200 y duration or 15−20 cm amplitude.

In other words, the rise in sea level observed over the past 150 years looks to be unusual in the context of the past 6,000 years. Particularly as the sea level rise isn't showing any sign of stopping. Quite the contrary, sea levels will continue to rise and by quite a lot as the ice sheets in Antarctica and Greenland continue to melt.

Yet to me that's not the most fascinating feature of the paper, probably because I'd pretty well figured that out (as you have too, no doubt). If you have the chance to read the paper, you'll get an account of what happened to sea level and ice going back way before the past 6,000 years - right back to 35,000 years ago, and you'll learn the basis of that account. The paper is still available here. I don't know for how long.

Climate and sea level: A life's work

The authors used data from many, many locations to create the history. Where there were gaps in the data, they used information from models to work out what probably happened. It has probably taken years of research. I notice that Professor Lambeck has been publishing papers on the subject for quite some time. David Mark interviewed him on ABC PM the other day, and opened with:

David Mark: "Several decades ago Kurt Lambeck, a Professor of geophysics at the ANU, set out to answer a question". 
Kurt Lambeck: "What is the relation between climate and sea level, and what can we learn about this? So it's been a long, long study that has taken us around the world."

Here is Figure 4 from the paper, showing what they term the ice-volume equivalent sea level plus more. Click to enlarge:

Fig 4. Solution for the ice-volume esl function and change in ice volume. (A) Individual esl estimates (blue) and the objective estimate of the denoised time series (red line). The Inset gives an expanded scale for the last 9,000 y. (B) The same esl estimate and its 95% probability limiting values. Also shown are the major climate events in the interval [the Last Glacial Maximum (LGM), Heinrich events H1 to H3, the Bølling-Allerød warm period (B-A), and the Younger Dryas cold period (Y-D)] as well as the timing of MWP-1A, 1B, and the 8.2 ka BP cooling event. (C) The 95% probability estimates of the esl estimates. (D) Estimates of sea-level rate of change. Source: Lambeck14

Near-field and far-field

In the above, you can get some idea of the how much data underpins the estimates of different periods. Fig. 1 in the paper shows the distribution of what the authors refer to as far-field sea-level data, which comes from lots of different places and lots of different sources. To explain near-field and far-field, I'll quote from the paper:
The sea-level response within, or close to, the former ice margins (near-field) is primarily a function of the underlying rheology and ice thickness while, far from the former ice margins (far-field), it is mainly a function of earth rheology and the change in total ice volume through time.

The data is much and varied in type and location. The paper goes into a lot of detail to explain how it was interpreted and how periods of sparse data were dealt with.

35,000 years of sea level history

Here is a bit of a summary of the changes in sea level and ice cover, but I urge you to read the paper itself if you are interested in the subject. The authors start their history at the beginning of the period they looked at. I've added my own commentary about what was happening to human society - and what might have happened had the world been like it is today.

Imagine if today's world existed 35,000 years ago. For around four thousand years, we'd barely have noticed the slight decline in sea level. We'd have plodded along - on less land, and being quite a bit colder than today, for many generations. Then suddenly we'd be faced with a rapid cooling and we'd find the sea level dropping by around 25 metres over the next 1,000 years.

For the next 8,000 years or so, from 29,000 to 21,000 years BP (before present = before 1950), we'd struggle on through cool climates. If we lived in Scandinavia we'd have built houses from ice and snow, or emigrated south to get away from eastward and southward expansion of the Scandinavian ice sheet. At the end of this period, the equivalent sea level was at its lowest point of the past 35,000 years, at 134 metres, "corresponding to ∼52 × 106 km3 more grounded ice—including on shelves—at the LGM [last glacial maximum] than today".

At last it would start to warm up again. The ice would start to retreat. Over a period of four thousand years or so, starting around 21,000 to 20,000 years BP, seas would rise - a lot. By around 10 to 15 metres before 18,000 years ago.

Things would settle down for a few generations. There'd be relative stability for about 1500 years from 18,000 to 16,500 years ago.

The next 10,000 or so years would see a major retreat of ice, from 16,500 years ago to around 7,000 years BP. The equivalent sea level would rise by around 12 metres each thousand years, with a total rise of around 120 metres. That's a lot of coastline disappearing. Had it been a modern society with today's world population, people would have had to keep relocating towns and cities inland further and further. But it wasn't. Human society was still in its infancy. It was during the latter part of this period that people moved out of the Stone Age and into farming.

During this period, about 14,500 years BP there was a very rapid rise in sea level lasting up to 500 years (maybe less). Seas rose at around 40mm a year. The paper states: "the globally averaged rise in sea level of ∼20 m occurs at a rate of ∼40 mm•y−1 or greater." That would have made life a bit difficult if people hadn't been fairly mobile and if there'd been the same population density as today. Which, of course, there wasn't.

Then there were some periods where sea levels rose, then steadied then rose again. After which there was a period from around 11,400 to 8,200 years BP "of near-uniform global rise". It rose a lot. Around 1.5 metres a century, and seems to have been fairly steady.  This would have been during the time when civilisations began. People started making tools out of metal, and farming.

The final phase of the North American deglaciation occurred around 7,000 years ago. It showed up in this research as a period of slower sea level rise - over the period 8,200 to 6,700 years BP.

From 6,700 years ago until recently (around 150 years ago), the seas rose but at a progressively declining rate. From the paper (my paras):
A progressive decrease in rate of rise from 6.7 ka to recent time. This interval comprises nearly 60% of the database (Fig. 1). The total global rise for the past 6.7 ka was ∼4 m (∼1.2 × 106 km3 of grounded ice), of which ∼3 m occurred in the interval 6.7–4.2 ka BP with a further rise of ≤1 m up to the time of onset of recent sea-level rise ∼100–150 y ago.
In this interval of 4.2 ka to ∼0.15 ka, there is no evidence for oscillations in global-mean sea level of amplitudes exceeding 15–20 cm on time scales of ∼200 y (about equal to the accuracy of radiocarbon ages for this period, taking into consideration reservoir uncertainties; also, bins of 200 y contain an average of ∼15 observations/bin). This absence of oscillations in sea level for this period is consistent with the most complete record of microatoll data from Kiritimati (23).
The record for the past 1,000 y is sparse compared with that from 1 to 6.7 ka BP, but there is no evidence in this data set to indicate that regional climate fluctuations, such as the Medieval warm period followed by the Little Ice Age, are associated with significant global sea-level oscillations. 
So, there you have it. A potted history of the seas and ice of the past 35,000 years. But do go and read the paper if you can. It's a lot richer in content than I was able to portray here. For example, the paper describes how the mantle changes as ice melts and forms. How the scientists were able to distinguish sea level rise and fall from land rising and falling (eg coral atolls). The paper gives an inkling of the painstaking research that must have gone into preparing this record. It reads like an adventure story - or as close as you'll get from a PNAS paper about sea level and glaciation :)

The denier protest

Of course the paper got a dumb protest from WUWT. What did you expect? Anthony Watts often claims the equivalent of saying that ice doesn't melt when it gets hot. It's pretty clear from his knee jerk reaction every time sea level is mentioned, that one thing that frightens him, probably more than anything else about climate change, is the prospect of rising seas.

This article was no exception. Of course he didn't read the paper. I doubt he even read his copy and paste of an article. First he copied some of what Eric "eugenics" Worrall wrote (archived here):
Claim: No change in sea level until modern times – but that change is dwarfed by sea levels of the past
Eric Worrall writes of a new paper trying to blame sea level rise on The Industrial Revolution, which started about 150 years ago:
The Australian National University has published a startling claim that sea level change has been more or less steady for the last 6000 years – until 150 years ago, when the sea started rising more rapidly.

I don't know where Anthony got the notion that the paper claimed no change in sea level until modern times. As you can see from the above, it said nothing of the sort. It was a detailed documentation of lots and lots of change in sea level over the past 35,000 years. In fact, his WUWT headline is contradicted by his second paragraph, where he writes that sea level change had been more or less steady. Maybe he can't tell the difference between steady change and no change. (How dumb is that!)

Nor do I know why they are startled to learn that the past 6,000 years showed fairly steady change. Maybe they figured that with temperatures dropping a bit for most of that time, that seas would have dropped to. I figure it's because ice and ocean currents can take some time to act in response to a gradual warming after the last glacial maximum. If anyone wants to chip in here, feel free.

Anthony pops in to his own article and adds his tuppence worth, writing:
But, other science suggests even higher sea levels during interglacials.
A paper published April 17th 2014 in Nature reconstructs sea levels over the past 5.3 million years and shows that sea levels were higher than the present during almost every interglacial period over the past 5.3 million years...

You'll recall how often people at WUWT claim that the world has stopped warming - based on the last (variously) 16, 17, 18, 19 or even 20 years of global surface temperature - what they call the "pause", though the hottest year on record was a mere four years ago. Suddenly Anthony Watts turns to a very different world, a world of five million years ago, as if to say "nothing to see here, move along".

He adds:
Sea levels during the last interglacial ~120,000 years ago were up to 5 meters higher than the present in this location and up to 9.5 meters higher at other locations (h/t to The Hockey Shtick)
So, if we had sea levels of 16-31 feet higher than the present 100,000 years ago, well before the dawn of the industrial revolution, what caused that? Inquiring minds want to know.

Anthony Watts doesn't have an enquiring mind or he would have looked it up. He's telling a fib there. He is also quite careless with dates, isn't he. Does he mean 120,000 years ago or 100,000 years ago? That's a 20,000 year difference, longer than the entire Eemian!

Okay, so let's assume he is referring to the Eemian, which is generally considered to be 130,000 to 114,000 years ago. The Earth as a whole was probably not much warmer than it is today, if it was any warmer. The difference between then and now, according to this paper in Nature Geoscience, is insolation. (Think Milankovitch, like Anthony Watts should have done.) The ice sheet in Greenland was thought to be something between 30% and 60% smaller than it is today. The authors worked out that probably about 55% of the ice loss on Greenland at that time was because of a global warming and 45% could be attributed to the much higher Northern Hemisphere insolation than is the case today.

There's another thing that Anthony Watts neglects. If the global surface temperature back then rose as high as it is these days, then the chances are that seas will also rise as high in the future. Most likely higher, even accounting for the fact that insolation is different, because temperatures these days are going up and up and up. Remember, the Eemian lasted around 14,000 years. That's long time. It wouldn't have got warm all at once. Almost certainly the warming was a lot more gradual than is happening now. Who really knows how the speed of change we're causing will affect ice melt? We do know that the West Antarctic Ice Sheet collapse has started and is considered to be irreversible. Greenland - the jury is still out on that. If we cut emissions enough soon enough, we may be able to delay things there or even prevent them altogether (though that's getting less and less likely as time goes by).

Anyway, even though scientists caution against it, because of the differences - if Anthony Watts keeps looking back at the Eemian, he could be drawing parallels as much as differences.

From the WUWT comments

There's a real lack of awareness in the comments. A lot of them don't stop to wonder that if seas could get a lot higher in the past, then what is stopping them from getting higher in the future, the way we're heating up the planet.

milodonharlani  takes a different tune to most WUWT-ers
October 14, 2014 at 4:37 pm
The whole premise of this laughable paper is wrong. The Industrial Revolution did not begin 150 years ago. It was already in full swing long before 1864.
It began with harnessing water power in the middle of the 18th century (eg, Kay’s flying shuttle, 1733, leading to Hargreaves’ spinning jenny, 1764), then increasingly switching to coal from 1763-75, with the development of Watt’s improvements on Newcomen’s 1712 steam engine.
Already in 1820-70 progress had advanced to the “Second Industrial Revolution”.

Contrast milodonharlani's comment with that from Frank (excerpt)
October 14, 2014 at 4:04 pm
...Even the IPCC doesn’t think GHG’s perturbed climate much before 1950. If so, sea level rise from 1850-1950 was caused by the end of the LIA. However, sea level rise over 1850-1950 is believed to be about 10 cm (4 inches). ...

Farmer Gez - really? Maybe Farmer Gez meant he heard Professor Lambeck interviewed on the ABC.
October 14, 2014 at 2:17 pm
I heard Eric Worrall interviewed on the paper. His main message was that the sea rise was due to expansion from temperature increase. The spin from our warmist Aussie ABC did not really fit Worrell’s rather unexciting observations.

O H Dahlsveen
October 14, 2014 at 2:40 pm
So, I wonder, what is the sea or “ocean floor” doing while the “sea level” is increasing? – Is anybody checking on that?

richardguy72  (no comment!)
October 14, 2014 at 3:45 pm
Isostatic Rebound is false as the Ice age myth, It is time that we realize that sea llevels were once much higher and covered the earth, Darwin was wrong and as a result the theory of Isostatic Rebound came to us through Agassiz who was also wrong by basing his Isostatic Rebound on Darwins mistake, Woe is us!! is anybody out there listening?
Richard Guy

gabrianga - I don't know if this is fact or fantasy, I haven't checked.
October 14, 2014 at 7:24 pm
The sea level in Kakadu National Park used to reach the top of the Arnhem Escarpment, between 400/600 feet where many of the Aboriginal residential and art gallery caves can still be found..
Now Kakadu is mainly floodplain at sea level with the Escarpment a sharp reminder of where the seas once reached.
Perhaps the IPCC can explain?

Kurt Lambeck, Hélène Roubya, Anthony Purcell, Yiying Sun, and Malcolm Sambridge. "Sea level and global ice volumes from the Last Glacial Maximum to the Holocene." Proceedings of the National Academy of Sciences (2014): doi: 10.1073/pnas.1411762111

Rohling, E. J., G. L. Foster, K. M. Grant, G. Marino, A. P. Roberts, M. E. Tamisiea, and F. Williams. "Sea-level and deep-sea-temperature variability over the past 5.3 million years." Nature 508, no. 7497 (2014): 477-482. doi:10.1038/nature13230

van de Berg, Willem Jan, Michiel van den Broeke, Janneke Ettema, Erik van Meijgaard, and Frank Kaspar. "Significant contribution of insolation to Eemian melting of the Greenland ice sheet." Nature Geoscience 4, no. 10 (2011): 679-683. DOI: 10.1038/NGEO1245


  1. Jesus Sou ! Your ability to swiftly secure a strangle-hold on a complex paper and encapsulate the guts of it in a few paragraphs is extraordinary.

    It's the sort of skill top silks at the bar strive to attain.

  2. Sou,

    "If the global surface temperature back then rose as high as it is these days, then the chances are that seas will also rise as high in the future."

    Sadly, his argument makes a certain amount of sense to me. The key is his statement, "So, if we had sea levels of 16-31 feet higher than the present 100,000 years ago, well before the dawn of the industrial revolution, what caused that?" Translation: it happens on its own and there's nothing that we can do about it. Milankovitch is the wrong card for him to play since it's currently going the wrong way, and therefore only to be used for things like the "CO2 lags not leads" false dichotomy.

  3. These people are still doing the whole "then what caused it to be warm at time x" routine? Seriously, in 2014? They've never heard or read explanations for the causes of glacial and interglacial periods? This coming from the audience that is completely sure that the worldwide scientific community knows nothing about climate science and only the source for real science is WUWT? How is this possible?


  4. Another one in the eye for the 'hot MWP' evidence deniers. No SLR = no global and synchronous "MWP" lasting hundreds of years.

  5. "The record for the past 1,000 y is sparse compared with that from 1 to 6.7 ka BP, but there is no evidence in this data set to indicate that regional climate fluctuations, such as the Medieval warm period followed by the Little Ice Age, are associated with significant global sea-level oscillations."

    I guess WUWT had to respond. Michael Mann hast to be the fraud that disappeared the Medieval warm period.

    1. Thanks, Victor.

      A relevant quote from the text - I knew there was something missing from my comment...


  6. Walking home from work today I read this and mused what it would be like for someone my age to have observed this over my lifetime.

    In those days, at my age I'd be one of the band elders, so the younger folk would listen with bemusement as the old man told them about how when he was a kid, the seashore was not as close, and you could get out to that little island out there without getting your feet wet, even at high tide. They wouldn't believe me, and I'd be a bit uncertain myself whether it was true or whether my memory was betraying me.

    Then I realized that even today, as a young man (thanks to our improved life expectancy), I can tell people that when I was a child, the snow held all winter long; we didn't have as many thaws in january and february as we do today. I'm pretty sure it's true, because these days we have climatological records carefully kept by experts.

  7. Here's one video the sceptics ought to be pleased to see. Jerry Mitrovica *thanking* them for asking questions which drive further research into SLR. Yes, really, thanking them. Funnily enough, the three boringly predictable issues he refers to have been decided in the negative by the research.

    He also mentions an earlier paper of Kurt Lambeck's which examined the sea level fish tanks used by the Roman ostentatious rich.

    The only problem with this is the sound - he turns away from the mike quite frequently so you have to either keep adjusting the sound or put up with it being very loud for most of it so you can hear the quieter portions clearly. https://www.youtube.com/watch?v=RhdY-ZezK7w

  8. Gee, you guys do waffle on about sea level rise. Poor old Sou is fretting about all these tipping points, and every time she posts on this we get the whole catastrophe thing happening. But it's always in the future, isn't it? Meanwhile in the real world, no sign of any real change in rates of rise for yonks, no clearly visible effects more broadly, and indeed even evidence that it just aint happening. All the high faluting papers in the world don't mean nuthin if you can't see something happening on the ground.

    Personally I'm with Spangled Drongo and his billiard table principle on this one.

    And I reckon the sceptics who suggest undersea volcanoes just may be onto something. I might have to go do some digging about that one, I must admit until just now I'd not really thought about it. But you know, I can see how it might have an influence.

    1. "...waffle on about sea level rise ..."

      And you expected what on an article about sea level rise?

    2. what's this about undersea volcanoes? what is it you think they are doing?


    3. Billy Bob - are you going to try to prove WUWT wrong (and all the scientists who've looked to see if the deep ocean is heating up and said it wasn't)?

      Good luck with that.

      On your way, see if you can figure out what happened to the CO2 that you must reckon has stopped obeying the laws of physics.

    4. "I must admit until just now I'd not really thought about it"

      We know. Whatever "it" is.

    5. "Personally I'm with Spangled Drongo and his billiard table principle on this one."


      For anyone who doesn't know what he's referring to, try this epic and amusing Deltoid thread where Spangled Drongo asserts his own special branch of marine climate science and the implications he wishes to draw from it whilst (as is his modus operandi) determinedly ignoring the extensive evidence - and even simply basic logic - that rebuts it and those implications. It's even more impressive if you read the "back story" Bernard refers to in this comment - and realise that Drongo by that point in time had been pushing his watery ideas up hill for three years or more.

      IIRC his special sauce includes:

      1) Sea levels vary by only about 30cm across the globe therefore because the sea is so large in comparison to that it is (relatively speaking) "flatter than a billiard table"
      2) In other words, "sea water 'aggressively seeks equilibrium'" which ends up being argued as "the sea is essentially at equilibrium".
      3) Which is argued to mean that all you need to disprove sea level rise is to measure in as few as one location where the rise is not clearly observed, even if there are a whole bunch of potential confounding factors (well laid out in the second half of this comment), and that then applies to the entire globe because it's so "flat" and "at equilibrium" (as expressed here, and on page 1 #61). You don't need any of this fancy schmancy science to try and carefully form a global picture and figure out the contribution of all sorts of different influences on sea level!
      4) And in fact, you can't accept any of that science because it is "junk science"(!). And he knows because his very small selection of carefully chosen local tide gauges are, and I quote, "...the only evidence anyone can verify.", despite one of those gauges apparently being nearly 7km from the river mouth (which Spangled Drongo claimed was 1 nm from the "official mouth" - which isn't the relevant metric for what affects the tide gauge anyway).
      5) And if you refute SLR that way, you also get to refute global warming! Really, it's simply not warming, it's just a bit of natural variation, because a couple of carefull chosen tide gauges including one 7km up a river say so!

      He even cites Nils-Axel Morner, at one point suggests that because he designs and builds boats he knows more about sea level science than the scientists do, and reckons that the climate system has negative feedback (in the engineering sense) that auto-corrects from any peturbation to the climate we humans prefer.

    6. But wait, there's more!

      Here's the first comment on that post where he introduces the comparison with a billiard table and the notion that "water aggressively seeks equilibrium", and the following comment which asserts that equilibrium has essentially been achieved ("Is that equilibrium or what?"), this suggestion that the sea must be flat because it's called sea level or
      this superb comment.

      And at one point after he (correctly) points out the the geoid is the correct reference for sea levels, he is pointed to a graph of sea level trends referenced to the geoid which show that they vary quite a lot over the globe. In response he says:

      "And that [graph] is what I have been trying to tell you-all about for days.


      OW it is ~ one hundred times flatter than a billiard table which shows to go just how flat and agressively in equilibrium our world’s oceans really are.

      So that if local SLs have not risen but actually reduced in Moreton Bay over ~ 70 years, there cannot be SLR in the rest of the world, accelerating or otherwise."

      ...which is precisely the opposite of what the graph in question shows. He simply refuses to twig to the very basic logical issue that arguing that the oceans are "billiard table flat, therefore sea level rise observations at one point apply globally" would mean that a single location where sea level has been observed to rise would mean that sea level is rising globally. If that's your logic, then you can't have it both ways!

      We're still not even half way through that thread, but that's the calibre of scientific "argument" that Billy Bob is touting...

    7. BTW, there is a Bolt for PM on that thread who is gamely (but only partly) trying to support Spangled Drongo. He also reveals that at Marohasy's blog that he posts over there as one Graeme M and confirms it at Deltoid.

      Interesting, given Billy Boy's temporary change of name below. Coincidence or small world?

      (And his claims at Marohasy's about the Deltoid thread are disingenuous to say the least!)

    8. Argh, "Billy Boy" => "Billy Bob".

      One might find it interesting to read the parts of that Deltoid thread discussing things with Bolt For PM, if he's really Billy Bob, noting the quality of argument made and even the fairness in quoting other people. There are some genuinely good questions, but there's also the rest and it seems fair to say that whoever he is, then due to the rest of it he doesn't cover himself in glory.

    9. Because of how he's been hogging these threads with his mix of science denial, concern trolling (which describes this particular series of comments) tone trolling, passive-aggressive demeanour, I did a quick Google. He's been commenting on climate blogs (or pseudo-climate blogs at least) for at least four years and has learnt not a thing in all that time. A typical lowest common denominator type of denier.

    10. If he really is Bolt for PM from that thread, then at a couple of points in that thread he appeared to understand a sprinkling of the issues with Spangled Drongo's position and "principle". And if so, he's apparently gone backwards in understanding since then, which is quite a feat. But I guess hanging around at Marohasy's blog will do that to you if you're not careful.

    11. Lotharsson, I learned a great deal through that long discussion at Deltoid. But I still think SD's broad principle is correct. I can't remember now where that discussion ended up, and I haven't been back to re-read it.

      But I never did understand why the BTP seems so hard to follow. It was a simple observation. The ocean is a fluid. Fluids seek to be 'level' according to the local effect of gravity. It is because of this that the ocean is generally thought of as an equipotential surface. We know that it deviates very little from the geoid, if I remember the argument I think the deviation is in terms of metres over the whole surface. Which makes the ocean surface smoother and more level than a billiard table, in a gravitational sense.

      That's how it is that the satellite altimetry Sou referred to works. It measures local variations in sea surface height against the calculated geoid to identify underwater anomalies which represent local structures such as seamounts etc whose grqvitational influence, however minimal, has affected the average sea surface height above the geoid.

      On that basis, SD argued quite cogently that sea level generally should follow the same trend globally over longer periods. It cannot just keep rising in one place over century time scales at complete odds with the rest of the world. Certainly, MEASURED sea levels using tide gauges may show that, but this must be due to local factors such as land subsidence.

      His example demonstrates that in his location, it hasn't changed much. I see the same at my location, which is not far from there. My town is built on a river which is tidal. On average, the river level varies with the tides and even in drought there is little noticeable effect on the water level.

      As far as I can tell, anecdotally of course, the river hasn't changed in well over 120 years. Photos of the time show the same wharves at around the same height above river level. No flood since 1890 has exceeded the height of the 1890 flood. Same applies at the actual seaside nearby.

      I don't argue that sea level is or is not rising, we have ample evidence it is. But the impact on the ground in my location is negligible. Following SD's principle, I have to wonder whether the real rise in GMSL is having similarly minimal impacts everywhere. What we see in terms of those locations where there ARE impacts are local influencing factors.

      That said, satellite altimetry DOES show a steady rise in SLR in the past 30 years, so if that is a response to global warming we can expect to see real local effects everywhere in time.

      Personally, I doubt that. But you don't. Sou especially thinks it will get worse, any day now. We shall see I guess.

    12. "But I still think SD's broad principle is correct."

      Then you really didn't learn as much from that thread as you think. It's a reasonable approximation for some purposes, but SD applied it with the presumption that it was a good approximation for his purposes (and which you also do), when it clearly is not.

      "It was a simple observation."

      Oh, no, it was so much more than that! There was the very notion of it being not so much "a simple observation" but "a principle" that one could employ to draw certain global inferences from local data, for starters. His argument was essentially "I reckon there's no real sea level rise in this one place on the earth, and I reckon it's an iron-clad PRINCIPLE that the sea MUST BE really really flat, therefore sea level simply cannot be rising anywhere else let alone globally because if it was by that principle it would HAVE to be rising here, regardless of how small the claimed rises are compared to the reported degree of flatness".

      "Fluids seek to be 'level' according to the local effect of gravity."

      As explained extensively on that thread, they don't seek anything, they respond to the sum of all forces acting upon them. That means they only tend to levelness if gravity is the only force acting on them. For sea water that's obviously not the case.

      Instead of thinking in absolute terms or "principles" like this you would be smarter to think of "how gravitationally level does the ocean actually get, and how do we know, and what are the best explanations for what we observe"? And once you think in those terms, you realise you have to measure the "degree of levelness" rather than assert "it's, like, really level".

      And strictly speaking that means the idea that it's quite level is not a universal principle but rather an observation which is only valid when the degree of flatness is specified, and hence that observation and degree of flatness are both subject to change over time. (You might then ponder the wisdom of SD accepting observations that say the ocean's level to a certain degree but rejecting observations using much the same methodology that find that it's also rising (and falling) at different rates in different places around the globe, those rates being entirely consistent with that measured degree of flatness.)

    13. "It is because of this that the ocean is generally thought of as an equipotential surface."

      Only if doing so is a sufficiently good approximation for your purposes (and as the article you're probably referring to points out, if you can ignore waves, winds, tides, ocean currents - all of which affect the local surface level). It is a good enough approximation (including ignoring those factors) for (e.g.) detecting quite large scale underwater structures such as "all volcanoes on the seafloor greater than about 1000 m tall".

      But if you're trying to detect much smaller magnitude LOCAL sea level changes over time it is erroneous to consider it an equipotential surface, because that presumption removes almost all of the variation you're trying to measure! As you point out the sea surface varies from the equipotential surface by up to a couple of metres. A metre or two is an enormous variation to simply approximate into non-existence for the purposes of your analysis when you're talking about local measurements of sea level changes that might range between no more than about -0.01m to +0.01m per year.

      "It cannot just keep rising in one place over century time scales at complete odds with the rest of the world. Certainly, MEASURED sea levels using tide gauges may show that, but this must be due to local factors such as land subsidence."

      There are two things to distinguish:

      1) Local factors that affect the raw sea level numbers obtained by whatever methodology is being used but are not indicative of actual sea level changes
      2) Local factors that actually affect the local sea levels.

      Sea level measurements used for looking at long term trends are corrected as much as possible for (1) because otherwise they're not reliable estimates of sea level. That means using land subsidence as an example is invalid if you're trying to discuss sea level data series suitable for measuring sea level trends over time, because it's a factor in category (1). That also means that the claim:

      "His example demonstrates that in his location, it hasn't changed much."

      ...is unjustified, as was repeatedly pointed out to both him and you on that thread, precisely because he completely refused to demonstrate that all of more than a dozen local factors there were listed for him had been taken into account in the (raw) measurements (and anecdotes) he was touting. In other words, he was not reporting a reliable sea level data series (and neither are you in your latest comment), so regardless of any other flaws in his argument it was already invalid because the data he relied on was not fit for that purpose.

      Putting that aside, if there category (2) factors, local factors that affect the actual local sea levels, and if they change over century time scales then of course local sea levels can change in one place - perhaps even your place or SD's place - "at complete odds with the rest of the world", which was also repeatedly pointed out to you and him on that thread! Water responds to all forces acting on it. You can only infer that (over some nominated time scale) sea level must be pretty much in sync everywhere across the globe if the sum of all forces acting upon sea water are in sync (over that time scale) everywhere across the globe!

      That point also invalidate's SD's argument, and he simply refused to deal with that point as well. Obviously he had to ignore both of those points because if you find someone who reports that their local anecdotes and uncorrected data show a marked rise, then by the very same argument he made referring to the Billiard Table Principle you have to conclude that the sea level must be rising EVERYWHERE, even at SD's place!

    14. Billy Bob / Graeme M misrepresented my understanding of projected sea level rise when he wrote: "Sou especially thinks it will get worse, any day now."

      Since 1992, sea level has been rising at 3.2 +/- 0.4 mm a year. That rate is likely to rise as ice sheets melt.


      If BB is referring to a very large increase from WAIS "any day now", I do not agree. Increase, yes. It's already happening. But the big increases won't happen in the short term, by all accounts I've read.

      The science suggests that the WAIS melt will start to exert a big impact later this century or early next century. Some reports suggest the impact on sea level could be fairly smooth (albeit significant, and quickly compared to past melts), while others suggest it could happen in jumps - a large increase followed by a relative plateau.

      If sea level were to rise by, say, 50 cm or more in a decade, followed by another 50 cm a short while later, and another - that would make life very difficult for a lot of people. And not just those who live on the coast. It will also disrupt shipping and transport, people inland will have to make room for sea level refugees, there will be huge pressures on economies and social structures world-wide,

    15. Lotharsson, this is dredging up stuff that now I don't recall that well, funnily enough I haven't read a lot nor studied the matter much since. So hopefully in responding I recall the science well enough.

      The geoid is a calculated surface that, relative to the reference ellipsoid, has variations arising from local gravitational influences. Those differences can be quite significant, I think in the order of hundreds of metres.

      The geoid is a much closer approximation of the true equipotential surface because it takes into account that gravitational influence. MSL used to be thought of as level in the same sense as the ellipsoid because water - the ocean - seeks equilibrium with gravity. We now know that while this is true, the gravitational surface actually has a lot of irregularities.

      Tidal datum are calculated over 19 year intervals or epochs. This is so the calculation averages out short term effects such as tides, winds and waves. The MSL so calculated is indeed generally free of those short term influences - they average to zero I think.

      This is what SD means by essentially level - the ocean is by definition level in terms of its relationship to the local gravity. MSL used to be considered zero elevation. Everywhere.

      As I said, the geoid gives us a better approximation of the true equipotential surface. As I recall, MSL varies from this by up to several metres, although I believe it is considered essentially equivalent at coastlines. That last point is important. In the open ocean, undersea structures have gravitational influence on sea level. Not so on coastlines, hence the general equivalence between geoid and MSL there.

      The point is that over long periods, the sea level approximates to the geoid, and on coastlines these two levels are pretty much the same (I think within 100mm or less though I have no references for that). Thus, the ocean 'aggressively seeks equilibrium'. This means that true sea level rise should, over the long term, be much the same everywhere. That is, the variation from the geoid at any location should be the same relatively speaking, although there could be gravitational effects in that same time as well (my sea mounts/lava/uplifts for example). If it rises 100mm from its previous relationship with the geoid at A, it should be ABOUT 100mm at B. That should not be the case so much on coastlines though. if it rises 100mm at one place, it should also rise 100mm at another place.

      If over long periods (a century), we observe a sea level rise in one location of say 300mm, but no rise at another location, then we should surely question why this wide variation. I contend that those variations are more likely to be explained by local influences because given the generally similar nature of coastal MSL to the geoid, the overall rise should be pretty similar. satellite altimetry should be good enough to uncover the real change in MSL, though I don't know that. I haven't done any deep reading on satellite altimetry beyond Sou's reference.

      SD's suggestion is that a stable sea level, or even a drop in sea level at his location over 80 years points to very little real change in MSL globally. I agree with the principle, but the observation ignores the possibility that locally, other effects might exactly equal or offset real SLR though that seems unlikely.

      So, as a principle, I think the BTP has merit. Why do you disagree? I've explained why I think short term effects of wind, waves and tide are averaged out, and I've explained why MSL closely approximates the geoid, and I've noted their essential equivalence at the coastline.

    16. This comment has been removed by the author.

    17. I came on a bit strong, in retrospect. Here is what I wanted to say:

      BB, if you want Lotharsson (or anyone) to pay your ideas attention then you need to give them the same respect you seem to want for yourself.

      Read what Lotharsson wrote. It is grounded in science. Give some sign that you've given consideration to the science and what other people here have gone to the trouble of researching. Think, read, learn.

      Or read this:


      Or look at this map showing where local seas are rising and falling:


      (Someone may have posted those links already. I've been away and haven't caught up with every comment.)

    18. Sou, I'm not sure I care that much whether Lotharsson gives my ideas any respect. I was just reiterating what I think was my position several years ago in a long thread at deltoid. Believe me, I've read all those references you have offered up and I think I have a fair handle on the concept.

      I understand exactly what Lotharsson is saying. Where I disagree is when he argues that over long periods we can have actual sea level rises that are out of kilter at different locations. I agree that sea level rises relative to a local coastline can, but the ocean surface is essentially level. With reference to gravity at any point on the globe. That is why we have a geoid and why MSL etc have been used in geodesic calculations. The sea cannot have long term fluctuations away from the local gravitational equipotential surface. Over time short term surface effects average to zero.

      If you think differently, show me a reference.

    19. BB: "If you think differently, show me a reference."

      I did already. You say you disagree with NOAA. That's your prerogative. I can't see that giving you any more references will change your mind. They'll just show the same as the ones you've already been given.

      From now on, Billy Bob / Graeme M / Bolt for PM or whatever you want to call yourself - you'll have to go elsewhere to boast how you deny science and don't "believe" observations.

    20. "The geoid is a much closer approximation of the true equipotential surface because it takes into account that gravitational influence."

      Kind of - the definition of the geoid is precisely that of a "true equipotential surface" (of which there are an infinite number at different distances from the earth's centre of mass). In particular it's a specially chosen equipotential surface that corresponds fairly closely to (but by definition is not identical with average global sea levels. In other words, when we say "geoid" we are talking about that definition - or we are talking about the measured value of that definition to as much precision as we can currently muster.

      "This is what SD means by essentially level - the ocean is by definition level in terms of its relationship to the local gravity."

      NO, NO, NO! It bloody well is not! I have pointed out that fact (and the reasons) here already, and it was pointed out on the Deltoid thread over and over again)!

      A neutral reader might be awfully tempted by this point to note that you appear to be determinedly and deliberately denying the distinction. They might also speculate whether that is because doing so means your entire argument falls in a very obvious heap, speaking of which:

      "SD's suggestion is that a stable sea level, or even a drop in sea level at his location over 80 years points to very little real change in MSL globally."

      As I already pointed out there are holes in that argument that you could drive a supertanker through. The most obvious one is that the argument SD and you both make NECESSARILY implies that a significant rise in sea level observed at ANY other coastal location in the world over (say) 80 years points to a significant real change in MSL globally.

      Wait, what?

      Crap, we have the very same argument saying that there must be "very little real change" in global MSL and that there must also be "significant real change" in MSL! There is only one conclusion that can be drawn. The argument is invalid for that data.

      You simply ignored that very obvious contradiction, so I think the level of denial you need to engage in to continue to assert your position is now obvious to all and sundry here.

    21. I don't think I want to go down this particular path again, but for the life of me I don't get why you disagree. Is it possible to take the discussion offline? I'd be happy to discuss via email, because there's something wrong with how one or the other of us are understanding what's being said here. On the other hand, if Sou is willing to indulge me, I am happy to continue the discussion here. What do you think Sou? If you don't mind me taking up space here, I'd really like to get to the bottom of why I am wrong in this one, because it just doesn't make sense what Lotharsson is saying.

    22. Graeme - you can continue the discussion under this new article on sea level.

  9. Billy Bob,

    "And I reckon the sceptics who suggest undersea volcanoes just may be onto something."

    Oh you mean like Ian Plimer .

    Now go watch Jerry Mitrovica in the video linked by adelady above.

    You could also learn something from reading 'Rising Sea Levels: An Introduction to Cause and Impact' by Hunt Janin & Scott A Mandia.

  10. Anon, the article addressed a paper that provides an insight into the sea level changes of the past 35000 years but also finds that sea level rise in the past 150 years is unusual. Fair enough. But whenever Sou posts on this matter, she always manages to slip in there some suggestion that SLR is a huge calamity just waiting to happen. Any day, err, decade, err, century now.

    I reckon that's waffling. Unless something happens, on past observations it'll keep rising at around the 2-3mm per year that it's been doing for the past 100 years. And there's no sign of ANYTHING catastrophic anywhere happening due to that.

    yes, in time it will have some impact, but not so's you'd notice.


    As for volcanoes, I went and had a look but couldn't find much. I assume though, given it's obvious even to a redneck like me, that it's been considered before. I was simply saying that the sceptics have a point. I don't know though how that point has been addressed and taken into account. I assume it has.

    I was more thinking that if general geological processes beneath the ocean must have an effect. For example, volcanic eruptions will deposit lava on the sea floor, raising the sea level. Subduction of plates may cause raising and lowering of sea floors with consequent effects on sea level. Earthquakes must do similar. Ditto the emergence of new islands caused by vulcanism.

    A read of wikipedia tells me that both the 2011 Japan and the 2004 indian Ocean earthquakes resulted in a substantial area of ocean floor rising by several metres. Hard to tell from the articles, but several hundred square kilometres by several metres in each case. The article on the Indian Ocean one even postulates a water displacement of 30 cubic kilometres.

    I'm not flash at maths, but if that was a permanent displacement due to the floor rising and not then settling back gives us around .3-.4mm sea level rise globally. If that similarly applied to the Japanese earthquake, then right there we have between .5 and .8mm sea level rise in the space of 8 years.

    Of course, like I said my maths is average so maybe that calculation is way out, but the idea remains. Raising the sea floor must raise sea level. As should all those other events.

    How has that been factored in?

    1. >I reckon that's waffling

      Nope, waffling is what you do Billy Bob. I write about facts and science (and link to sources).

      The reason you can't tell the difference between waffle and fact is probably because, as you've admitted before, you don't understand the first thing about science.


    2. Billy Bob, there's an FAQ on U Colorado sea level website that should answer some of your questions. It has links to further reading, too.


      More here at CSIRO, also with links to further reading:


      And some at NOAA, with links in the side bar:


      Plus some at NASA:


    3. Billy Bob

      Your cheek is amazing. To say people are waffling about sea level and then waffle about yourself for 8 paragraphs ...

      "I was simply saying that the sceptics have a point."

      Yes, the real sceptics had a point some considerable time in the past and have investigated and factored it in. The fake sceptics do not have a point - they just keep raising false points again and again, however many times they are debunked, to spread uncertainty and disinformation for mugs like you to lap up. So, yes, by all means go and look up what has been done. If you have any genuine questions (as in not fuelled by denier websites) raise them and ask them. You could start by being sceptical of your own thoughts above. How much would 30 cubic kilometres raise sea level? You can then check your answer against results you can research. e.g. Lionel's recommendation above 'Rising Sea Levels: An Introduction to Cause and Impact' by Hunt Janin & Scott A Mandia. If you find a discrepancy then research some more. Then perhaps you might have something worth saying. Eventually, say in about 10 years time, you might even publish a worthwhile paper. By then you might look back on your young self and wonder how you could have been so .

    4. ...fill in adjective of your choice...

    5. Billy Bob, you might be interested in this, too:


    6. Yes, that one is interesting. Your earlier links didn't address short term events but covered plate tectonics. This one seems also focused on tectonic activity but I need to make the time to read more closely. But may very well provide some insight to my questions. I remain curious about the effect of localised extreme events tho. i recall reading of a new island being formed from a volcano some years ago, it all happened very quickly as I recall. It's not a stretch to imagine a lot of that sort of thing under the ocean. While one such has little impact, many might be a different story.

    7. BB the links were to help you answer your question "How has that been factored in" (by people who measure the mass of water, the height of the sea, the depth of the sea floor). Read, then think about it.

  11. Billy Bob

    It was no more than 1C - 2C warmer globally during the last interglacial (the Eemian) that it is now. Mean sea level was >5m above present levels. There is a cause-effect relationship between temperature and MSL.

    Of course it will take a century or two for radical SRL to occur but it will still be a disaster for humanity. So the general idea is to avert this disaster by reducing CO2 emissions. It's conceptually very simple, really, unless you believe that BAU emissions will not result in ~2C temperature increase by the end of this century (that is a very conservative, almost lukewarm estimate btw).

    All you have to do is think.

  12. Actually, I think Billy Bob the archetype ought to start with Weart's book. That's a sincere suggestion; do read it, BB. If you're left with objections to what you read in Weart's book, you'll automatically be equipped to offer better-informed critique.

  13. Hmmm... so anonymous above can't even read my short comment eh? Dill. I 'did' work it out but who knows if I am right, my math is lousy. My point wasn't that specific event, I raised an obvious question based in physics. Not one of you addressed that. Except Sou whose links I will have a read of.

    Now, I don't care a whit whether what I asked has any basis in fact. It was my curiosity that caused me to ask, I figured you rabid catastrophists would know if that possibility had been considered and addressed in the past.

    My admittedly short search found plenty of references to the heat of undersea vulcanism and that's been well addressed. But I couldn't quickly see any reference to the matter of undersea intrusions.

    Simply put, if the sea floor rises, then so too will sea level. Has that been factored in. You cannot say to me "But Billy Bob, that's not true". it quite simply is.

    Now anonymous old pal, as I read it, those two earthquakes I mentioned raised several hundred square kilometres several metres. But there were no actual detailed figures. Based on the figures in those wiki articles let's go with as much as 1000 sq km. Each article suggests around 300-500km by maybe 100-200 km uplifted. That could therefore be as much as 1000 sq km. Let's assume 2 metres of lift. This gives a cubic volume of potentially 200 cubic kilometres. That, according to Billy Bob's notoriously poor maths (for which he was awarded dummy of the month in high school), equates to around 2mm of sea level rise. You'll recall in my earlier post I had figured that 30 cubic km = .3 mm slr, so 200 gives us around 2mm.

    Go do the calcs yourself and tell me what you get. I am probably wrong.

    My point is not my maths skills, it is that physically, any increase in seabed height must raise sea level.

    Has that been factored in? My calculatiopns, rough and derisable as they are, suggest that depending on the quantum of undersea events, the effect on slr could be significant.

    It probably makes little difference and frankly I don't care. It was what passes for intellectual curiosity in my loungeroom. I am sceptical that the sensitivity to CO2 is high and doubt that humanity will increase emissions that much more in the coming century. Given that increasing CO2 from what, 280ppm to 400ppm has made no appreciable difference to sea levels, I for one am not losing any sleep over it...

    1. Billy Bob

      Has that been factored in? My calculatiopns, rough and derisable as they are, suggest that depending on the quantum of undersea events, the effect on slr could be significant.

      What undersea events? We are, by definition, talking about a pretty major displacement of seawater here exhibiting an ongoing trend. Discrete events don't drive a trend unless they are occurring continuously. I suspect that if ocean basin geology was sufficiently active to drive a trend like that observed - enough to raise MSL by ~3mm/y for over two decades - we'd have noticed it by now.

      This sort of thing makes a great deal of seismic noise.

    2. BBD you misunderstand. I am not suggesting sea level rise on the whole is resulting from seabed activity. You are right, an ongoing trend must result from an ongoing cause and increasing ocean heat content must play the greater part.

      I AM saying that what happens on the seafloor could be a confounding factor. I just used two notable examples. There is considerable undersea activity at all times, remember the sea covers 70% of the earth's surface.

      We have tectonic plate activity, earthquakes, volcanoes and so on. The Pacific Ring of Fire is constantly active, do you have any idea of the volume of lave being extruded, or the extent to which undersea earthquakes are raising the sea floor? What's happening in the deepest trenches?

      Did you see Matty England on catalyst telling us how sea level rise is very noticeable locally around the NW Pacific? Check the rates of SLR, see that spike in 2011? How do we know that the mouind in the NW Pacific isn't related to that 2011 earthquake event?

      That event moved Japan, widened the continent, and uplifted a monster portion of sea bed. How long would it take for the displacement of sea level post that event to propagate throughout the world's oceans?

      I have no idea, perhaps England's mound and the spike in global SLR is a response to that event. Perhaps we'll see a reducing trend in the next few years as that water dissipates.

      And maybe there is no relationship at all.

    3. Billy Bob

      Why can't you post like a normal person? If you were really curious and looking for answers you would treat the people you are asking with respect. And then you might get some respect back. Calling people "rabid catastrophists", saying you "don't care" and then muddling the post with comments about "not losing any sleep" do not mark you as an honest enquirer.

      You are right. I cannot be bothered to address your points. But that is because you do not convince me you are being genuinely inquisitive.

    4. Billy Bob

      There is considerable undersea activity at all times, remember the sea covers 70% of the earth's surface.

      You are still arguing for the trend in SLR being significantly influenced by a trend in seabed geological activity.

      There's no evidence for such a trend, or at least, none that I can find. If you can find any, please link.

      Did you see Matty England on catalyst telling us how sea level rise is very noticeable locally around the NW Pacific?

      I didn't but it doesn't matter. Sea level change differs from basin to basin and within individual basins for lots of reasons. Major wind patterns, temperature and salinity of the water, ocean circulation and the geoid all influence sea level.

      How do we know that the mouind in the NW Pacific isn't related to that 2011 earthquake event?

      For the sake of argument, let's say that it was. It won't have any significant effect on the long term global trend.

    5. BB, from your Wikipedia reference, the 2004 Indian Ocean earthquake ultimately raised the global sea level by around 0.1mm. Checking that out. The volume of the oceans is 1.3 x 10^9 cubic kilometres, has an average depth of 3.7 kilometres and a surface area of 3.6 x 10^8 square kilometres ( ocean. You've estimated that the volume of ocean displaced by the seafloor uplift from India 2004 was 200 cubic kilometres. (According to Indian Ocean earthquake, the estimated volume of ocean displaced was 30 cubic kilometres as you've pointed out.) The sea level rise that your estimated displacement would have caused is the volume rise spread evenly over the ocean's surface or 200/3.6 x 10^8 kilometres or 5.6 x 10^-7 kilometres or 0.56mm. (Based on the 30 km^3 figure, that would have been a 0.084mm sea level rise or 0.1 mm.) As for the Japan 2011 earthquake, you may be able to find an estimate of displaced ocean and do your own calculation. It's a tricky one as there was land subsidence as well as seafloor uplift.

      Volcanoes depositing lava on the ocean floor is also tricky. As the lava cools it contracts, loses volume, becomes more dense and its weight causes deformation of the ocean floor below it. And, to my meagre knowledge, undersea volcanoes come from rare ocean plate subductions so the deposition of 'lava' is more likely to come from seafloor spreading. Seafloor spreading is associated with mid-ocean ridges which, if the spreading is fast, causes ocean floor uplift and a seafloor subsidence if slow. Geologic hotspots could cause volcanoes as happened with the Hawaiian island chain but they've been around for millions of years so their impact on sea levels is probably irrelevant to the last 100+ years. The changes in sea level caused by seafloor spreading are of the order of mm/ka or m/Ma which is a lot less than mm/da and are similarly irrelevant. Given the dimensions of the world's oceans, the influence of volcanoes on sea levels is probably irrelevant too except on a geologic scale, if at all.

    6. Thanks GM, your calculation is correct, I was way wrong. But interesting in that you agree there would be an effect on SLR.

      Disregarding for a moment whether there was a net uplift in those two events, the change could have been in the order of .5mm over 7 years. Again, I am not making any claims, just observing a fact.

      What would the combined total of all such events across 70% of the globe's surface in any given year be? Minimal as you suggest? We don't know, that's just a guess. But by your own calculations we have potentially half a mil over 7 years from just two events. I will try to do some further reading - not because, Jp, I want to prove anything, just because I am interested to find out if my thinking is good. Which so far, it appears to be.

      GM, I don't know much about undersea vulcanism, but why do you suggest it is only related to 'rare ocean plate subductions'? Volcanoes occur on the surface in a variety of locations not always associated with plate subductions, why should it be different under the sea? Your point about Hawaii is taken, but active events of that nature have taken place recently. Surtsey is an example. http://en.wikipedia.org/wiki/Surtsey

    7. Billy Bob / Graeme M

      Multiple handles don't look good. People with think you are a troll.

      You are *still* blanking the point, so I will repeat it yet again:

      There is no continuous string of major earthquakes raising the floors of the major ocean basins every year. Therefore the multi-decadal trend in SLR **cannot** be explained by such a mechanism.

      Read the words. Give the thermal expansion denial a rest. It's boring.

    8. Sou please quote where at any time I suggested that either earthquakes caused the broad trend or that I deny thermal expansion. If you csn then we can give your comment some credibility. Otherwise...

    9. Graeme, to which comment of mine are you referring?

      As for your comments, there's this wild extrapolation based on no evidence whatsoever:

      Disregarding for a moment whether there was a net uplift in those two events, the change could have been in the order of .5mm over 7 years. Again, I am not making any claims, just observing a fact.

      What would the combined total of all such events across 70% of the globe's surface in any given year be? Minimal as you suggest? We don't know, that's just a guess.

      Then there's this equally wild speculation:

      I have no idea, perhaps England's mound and the spike in global SLR is a response to that event. Perhaps we'll see a reducing trend in the next few years as that water dissipates.

      And this:

      Simply put, if the sea floor rises, then so too will sea level. Has that been factored in.

      Then there's this mixed up contradictory spectacular:

      So while I don't think it affects the overall trend in SLR, I DO speculate about the extent to which those events might affect the trend. And I wouldn't be at all surprised to find it a relatively constant background effect.

    10. Sorry Sou, it was BBD I was responding to. Mind you I think your effort is way off-beam too :)

    11. Billy Bob / Graeme M

      Stop wasting everybody's time.

    12. "Now, I don't care a whit whether what I asked has any basis in fact." and bye, bye.

    13. Gee, there's no stopping you guys once you work up a head of steam is there? Let me repeat this slowly, and perhaps in words of few syllables so's you can follow it (are you listening BBD?).

      1. I am not suggesting that undersea geological activity is causing the current rise in sea level over time.
      2. I am not denying the contribution to sea level rise of thermal expansion.
      3. I am not denying that melting glacial ice is contributing, or might contribute in future, to sea level rise.
      4. I AM wondering aloud whether undersea geological activity contributes to sea level rise, and if so what is the magnitude of this. So far, no-one has offered a single reference to this one way or the other.
      5. It is simple physics that if the sea bottom experiences localised surface rises, those rises must displace an equivalent volume of ocean which must therefore raise sea level.
      6. it is similarly simple physics that any object floating on the surface of the oceans will similarly displace volume and hence raise sea levels.
      7. The example of the two earthquakes illustrates the question of the extent of such activity, and the extent to which it may or may not contribute to sea level rise.
      8. The only person willing to offer a calculation, George, finds that IF those two events raised an area that displaced 200 cubic km of ocean, the sea level rise would be something like .56mm. That is potentially .28mm per event, or averaged over those 7 years, .08mm per year. Nearly .1 mm/yr. Given that glacial isostatic adjustment is, averaged globally, in the order of .3mm/yr, those numbers are not insignificant.
      9. This postulation is just that and is largely uninformed by more than a quick look at Wikipedia. I wondered at the extent to which this activity might or might not affect SLR. I did not say that it does, nor that I have any well formed idea of magnitude nor any substantial evidence. On the contrary, I asked if anyone could point to references that it has been considered as a factor and discounted. No-one has provided such a reference.
      10. George M wondered at the prevalence of such undersea activity. I agreed that I do not know. But given the amount of ocean floor that covers the earth, some 70% of total area, I suggest it may be more substantial than other commenters here think.
      11. Here is a link to an article about another interesting event in 2012. Further evidence that such events may be more common than my fellow commenters here are suggesting: http://www.smh.com.au/national/education/havre-eruption-leads-scientists-to-biggest-undersea-volcano-20140509-zr7dw.html.

      In summary, I make no claim. I suggest a possibility and ask where there are references to the consideration of that possibility. I pose a clear statement of why such an effect may occur, based on simple physics.

      I also don't care whether the idea holds water or not. By that I mean that I have no vested interest in the outcome. If such effects have been scientifically considered and discounted, then great. I'll file that away in my ever expanding catalogue of great sceptical ideas that didn't fly! :) That is what I meant by your quote, cRR Kampen (another comprehensionally challenged contributor to this blog).

    14. BB you are missing the point either deliberately or inadvertently. I'd guess the former going by your past form.

      The point being that there is no evidence to suggest that volcanic activity under the ocean is any different now to what it has been for the entire Holocene (or earlier). If it is no different now, then it won't have any net effect on sea level. The ups and downs are not only minute, they balance out.

      And to cite a "once in a century" event as "more common" than your fellow commenters are suggesting is wrong. No-one has, AFAIK, discussed how common are undersea volcanoes - only that there is not any evidence to suggest that the frequency or magnitude of such events has changed. (Logic is not your strong suit, is it.)

      As for not making any claim - you are making a claim. You are claiming there is a possibility that volcanic activity has suddenly increased in frequency and/or magnitude in the last several decades.

      It is incumbent on you, not anyone else, to provide evidence supporting your speculation. While an absence of evidence is not evidence of absence, the sums on thermal expansion + glacial melt +/- post-glacial adjustments are already done. So you'll have to not only point to evidence to support your speculation, you'll have to point to what happened to the water that is calculated should be there, that got displaced by your speculative upheaval of the sea floor.

      You do have a vested interest in the outcome. You have admitted (implicitly and/or explicitly) to being by inclination a science denier. You have a vested interest in "anything but CO2" that deniers are so fond of.

      You've written multiple comments all saying exactly the same thing. You've provided not one jot of evidence to support your speculation.

      You might as well say that it's possible that earth is spinning out of orbit. Not that you'd have any interest in the outcome one way or another, but you want someone to prove that it's not spinning out of orbit.

      And you'll write ten or more comments begging people for proof that the earth isn't spinning out of its orbit. You aren't saying that it is spinning out of its orbit. You are just raising the possibility and you want someone to do the sums on your behalf to prove that it's not.

      Ad infinitum.

    15. Graeme M --- George is off by a factor of 1000.

      He wrote, "5.6 x 10^-7 kilometres or 0.56mm." except milli is 10 to the -3, micro is 10 to the -6. The calculated sea level rise over the world's oceans would be 5 thousandths of a mm or 0.00056 mm.

    16. Uhm, Kevin, km to mm is a factor 10^6.

    17. Graeme M / Billy Bob

      Denial denial is even more tedious than acknowledged denial.

      Stop wasting everybody's time.

    18. BBD, did you see this?

    19. I did! Well spotted/remembered. 'Bolt for PM' the one-time Spangled Drongo endorser seems to be our man Graeme M the Billy Bob.

      Coincidence or small world?

      Actually, that's a sock, old chap!


    20. Kevin O'Neill, I think you are wrong. George is right.

      Sou, I think it is you whose logic is off. First no, I made no claim, I asked a question. I don't know the answer. Nor do I care what the answer is, it is curiousity only.

      You argue that undersea activity is likely no different now to any other recent time. That may well be correct but it's a claim that you make with no evidence. Show me your references.

      You also claim it could have no net effect, but again this is based on no evidence. If it is small, say less than 0.1mm per/year, then of course its effect is not noticed against the broader trend whether that be up or down. Scientists did not include the GIA in GMSL until relatively recently, yet we must presume it was always there.

      You also argue it is incumbent on me to provide evidence. Say what? I repeat, I don't care. I asked a question. No-one can answer. That's OK, we can leave it at that.

      BBD old clot, I have no idea what a sock is, but yes, I am indeed the poster Bolt for PM from that long ago utterly bizarre thread at Deltoid.

      Sea level is an intriguing matter. At an ideological level I have no stake in whether it rises or it falls. I am not a policy maker that has to consider the impacts. My curiosity is just that. And I think, and continue to think, that SD has a point.

    21. There you go again. Read my comment again. And again. Then if you still don't get what I wrote, ask someone else to explain it, in its entirety.

      As for your claim you don't care, your actions here and elsewhere betray you.

      (Liar, liar, pants on fire.)

    22. Billy Bob Graeme M argument in summary:

      I made no claim, I asked a question. I don't know the answer. Nor do I care what the answer is, it is curiousity only. repeat, I don't care. I asked a question. No-one can answer. That's OK, we can leave it at that. At an ideological level I have no stake in whether it rises or it falls. I am not a policy maker that has to consider the impacts. My curiosity is just that. In summary, I make no claim. I also don't care whether the idea holds water or not. By that I mean that I have no vested interest in the outcome. If such effects have been scientifically considered and discounted, then great. Now, I don't care a whit whether what I asked has any basis in fact. Again, I am not making any claims, just observing a fact. not because ... I want to prove anything,
      And maybe there is no relationship at all.

    23. Oops, GM! (@ October 21, 2014 at 6.29 am) Poorly worded on my part. In very general terms and within the limits of my understanding, ocean vulcanism can be caused by sea floor spreading, subduction and by hot spots or plumes. Volcanoes on land mostly come from plate subduction (subducted ocean plate melts, less dense parts rise through more dense magma, etc), some from intraplate hotspots and, as in the case of Surtsey, from (the Mid-Atlantic) ridge spreading in a shallow sea. Sea floor spreading produces most oceanic volcanoes. Vulcanism can result in basaltic lava extrusions which fill the space left by the sea floor spreading, see here.

      With seafloor rise there will be an effect on SL, as you are contending, but will the effect be permanent or temporary or transitory? Relying on better wordsmiths than moi. Less than an hour before the eruption, the seafloor saw an abrupt uplift of 2.75 inches (7 centimeters). After the eruption, the seabed deflated by more than 6 feet (2 meters) as the magma flowed into the oceanic crust and erupted as lava (See here) A similar effect is seen with subduction. The part of the crust nearest to the fault zone rapidly moves upwards by a metre or so, lifting the entire body of water above it. A hundred kilometres away the opposite may happen: the seafloor drops and the ocean above it also falls in the process of subduction-generation of a tsunami (+ 30 sec. video). The sea floor drops as a result of dynamic subsidence of the lithosphere and the associated infill of water to this area may compensate in part for the sea level rise.

      To my knowledge, the mechanism for the above uplift linked with subsidence of the sea floor involves mainly Archimedes Principle and gravity with an invocation to Pascal's Principle, if necessary. When a less dense plume from a subduction or geologic hotspot rises up (Archimedes Pr) through the mantle and eventually through a continental plate or oceanic plate, more dense material from nearby in the mantle moves in to the space that the plume leaves behind as it rises. This movement of replacement material is gravity induced and is repeated through the mantle until somewhere nearby there is a crustal slump. This mechanism occurs within the rock cycle. In a similar manner, this applies to a mid-ocean ridge replacing crust as subduction removes crust.

    24. But wait, GM, there's more which is probably more direct than the previous post. In the case of the Icelandic island Surtesy, here's an estimate of its impact on the global sea level using a topographic map of Surtsey, its maximum size 2.4 km^2 (1967) and the 130 m depth of ocean it sits in. I'm assuming that its base is a 'generous' 14 km^2 (which includes the nearby islands of Jolnir and Syrtllinger), it's completely solid without fissures in its flanks, its underwater flank has an average angle of 10 deg to the horizontal and its shape is that of a cone. In which case its volume below sea level, including the volume of nearby islands Jolnir and Syrtlinger, is 1.1 km^3 and its total contribution to sea level rise is 0.0031 mm.

      Extending this to undersea volcanoes, there is an estimated annual 3 km^3 of lava added to the ocean floor by mid-ocean ridge volcanoes. Which translates to a annual contribution to sea level rise of 0.01 mm (3 x 0.0031), assuming there is no compensating crustal subsidence for the lava extrusion. From the reference in the same link, it's estimated that ridge spreading adds an annual 10 km^3 of new crust to the ocean plates (this includes the lava from volcanoes); putting this in perspective, the average volume of lava extruded by Kilauea each year is about 0.1 km^3.

      Hope that clears up some loose ends.

    25. Thanks George, that's some nice solid info. And all with references and not a single nasturtium cast. Your reference to the 3 cubic km of lava is a good read, as is one of Sou's references which led me to a very interesting site regarding satellite altimetry and plotting the topography of the sea floor.

      So the answer to my question - is it a significant effect - is a resounding no.

      One thing I will say is that from some other digging I've done, significant earthquakes, volcanic eruptions and island building are much more common than 'once in a century' events, which is an interesting thing in itself.

    26. BB in the newspaper article you linked to upthread, a scientist described that particular volcanic eruption as a "once in a century" event. You know, in your comment where you said volcanoes happened more often than some (unnamed person or person) claimed, despite nobody here claiming anything remotely related.

    27. Dunno Sou, that's a funny point to get hung up on. I wondered at the extent of a background effect from undersea activity. You and others generally argued it either wasn't significant, or that the larger events like the earthquakes or volcanoes were relatively infrequent. BBD in particular suggested that when he said, in an evidence free assertion plucked presumably from a centre of ignorance he finds beneath him when he is seated, that:

      "there is no continuous string of major earthquakes raising the floors of the major ocean basins every year."

      I asked for references. So far, only George M has supplied any references which gives us some sense of the scale of events. But even so, the question of the frequency of said events has not been clarified to any extent.

      In the context of your comment, you have again selectively misquoted me. I did not claim that volcanoes happened more frequently than a scientists said. The scientist was referring to a significant event, the birthing of an island, as a once in a century event. A Google search will show you that new islands arising from volcanic activity certainly occurs more than once a century, there are at least several this century alone. So I suggested that maybe such events occur more often than people think.

      Note too that I was commenting in relation to George's suggestion that such activity as major eathquakes or eruptions is probably relatively infrequent or minimal. However George's own reference shows that typical undersea volcanic activity, as distinct from major events, produces some 75% of global annual magma extrusion, so it is clear that the background activity in the oceans is actually quite significant in frequency, if not in scale.

    28. If there's no trend in undersea geological activity it cannot be causing a trend in sea-level. Any such trend would be noticed by geologists. No such trend having been noticed, you'll have to dream up an alternative.

      Have you considered the recovery in whale volume as a contributing factor? I doubt there's any specific evidence to the contrary so you can hug that one to yourself indefinitely.

    29. BB is trying to squirm his way out. Anyone who could be bothered reading the entire thread will see how he misrepresents not just himself ("it's volcanoes" "it's earthquakes"), he misrepresents everyone else too, claiming they said stuff they didn't.

      He's not a master of deception. He can't do it very well at all. He does score highly on the verbal diarrhoea scale.

    30. Sigh... how is it you guys can post seemingly intelligent, well-researched comments when you all agree with each other, but as soon as you start arguing with someone who doesn't, you go off the rails?

      Cugel I never said that undersea activities, whether earthquakes, whales, or US submarines, influences the TREND. I suggested that the activity might affect sea level. Quite a different thing. Like GIA, it could be a minimal adjustment factor. Or, it might be a one-off irregular contribution such as the Indian Ocean earthquake.

      I even said, quite clearly, that the broader trend must be due to thermal expansion and glacial/ice pack melting.

      As for your mischievous misquoting Sou, well... can't help you there. Must be a cognitive thing eh?

    31. I expect as soon as you clicked "publish" you had an "oh shit!" moment, BB/Graeme.

      Just in case you didn't, what did you mean by "sea level" when you wrote:
      Cugel I never said that undersea activities, whether earthquakes, whales, or US submarines, influences the TREND. I suggested that the activity might affect sea level. Quite a different thing. Like GIA, it could be a minimal adjustment factor.

      To most of us, certainly to me, that makes no sense. I don't mean it's wrong. I mean it's nonsensical. It's "not even wrong". You are arguing that at some time scientists calculated the global mean sea level, added a plus or minus to allow for earthquakes and volcanoes, then set a new global mean sea level.

      Just what to you understand when scientists talk about sea level and sea level trends?

      Might as well comment on your "I never said" bit while I'm at it. You are contradicted here in your very first comment, for example, when you said: ""And I reckon the sceptics who suggest undersea volcanoes just may be onto something."; and here, and here. In nearly all your comments you were speculating that seismic activity under the ocean impacted sea level rise, eg in another comment you wrote: "My calculatiopns, rough and derisable as they are, suggest that depending on the quantum of undersea events, the effect on slr could be significant."

    32. Always amusing when someone blows their sock-puppet anonymity out of the water.

    33. Gee... I find this exchange fascinating, perhaps in person we wouldn't have this confusion.

      All I meant was that the broad trend is up, not down or stable. That is largely caused by thermal expansion and ice melt. If there were an effect from undersea events on sea level, it might affect the trend rate (or the degree of trend if you like), but I cannot imagine it being substantial enough to affect the broad trend.

      That's it. Just like the GIA is an adjustment against the trend rate but doesn't affect the overall trend.

      I guess not being a scientist means I am sloppy with the language, so I apologise for that.

      KR, what is a sock-puppet?

    34. Billy Sock

      There is no continuous string of major earthquakes raising the floors of the major ocean basins every year.

      That's a matter of established fact.

      Don't like it? Post evidence that contradicts it. Telling me I am talking out of my arse doesn't count, although it does reveal that you have no evidence-based counter-argument. But we knew that already.

      You have persistently insinuated that seismic activity *is* a significant contributor to sea level trend while claiming that you are doing no such thing. You have been doing it since your very first exchange with me on this thread and I have been telling you to stop since that exchange. You are being transparently dishonest and you are wasting everybody's time.

      BBD old clot, I have no idea what a sock is

      You are also using multiple screen names - aka "socks" or sock-puppets - which is standard practice for trolls and time-wasters seeking to hide their history of dishonesty from moderators and other commenters.

      So in summary, you are being dishonest, you have no evidence to back up your claims and you got caught running a sock on this thread. I'd say it was time to fold up your tent and go.

    35. BB/Graeme, you don't know if you are coming or going, do you.

      First of all you speculated lots of times that seismic activity under the ocean is contributing to sea level rise.

      Then you denied saying that and said it affected sea level once off, and asked if it was adjusted for. Which makes no sense.

      Now you are contradicting yourself when you write:

      "If there were an effect from undersea events on sea level, it might affect the trend rate (or the degree of trend if you like), but I cannot imagine it being substantial enough to affect the broad trend."

      What you are now saying is that seismic activity isn't just making seas rise, it's making them rise faster ("trend rate"). In other words, you're arguing that seismic activity isn't just causing the sea level to increase, each year it's causing a bigger increase in sea level this year than last year, which was bigger than the year before etc. But at the same time you say it wouldn't affect the broad trend. Which is a contradiction.

      I think you should take a break and give your brain a rest - quit before you get any further behind. While you are resting, think about the meaning of: "trend' vs "trend rate" vs "increasing trend rate" vs "positive/negative trend" and other variations. (Think: velocity vs acceleration - if that helps.)

      Oh, and while you are giving your brain a rest, or exercising it with trends, ask yourself:

      1. To what extent seismic activity would have added to sea level over the last, say, one hundred thousand years, assuming no change in the frequency or size of seismic events over that time. In other words, there were as many earthquakes and volcanic eruptions each century, and the average impact each century was the same.

      2. How would that affect the land mass.

      3. How would it affect the shape of the earth and the size of the earth.

    36. @Billy Bob Sock Puppet and/or Graeme M sock puppet. You decide.

      "KR, what is a sock-puppet?"

      You don't know what a sock puppet is? But somehow you know the comment is aimed at you? If a comment is not named then by default the comment is probably aimed at the person who started the thread - which is Billy Bob, not Graeme M.

      Such innocence!

    37. GM, some information for you. But first, "the background activity in the oceans is actually quite significant in frequency, if not in scale." is irrelevant as frequency has a time dimension and scale has a length (cubed) dimension. In other words, submarine volcanoes could be going off like fireworks but, unless there is a large volume involved, the impact on sea levels is minimal. And, hovering in the background are geological processes which can't be ignored. Which leads to:

      Sea floors are covered in water-saturated, non-consolidated sediments and depending on depth. It can be difficult for lava dykes to actually reach the sea floor. The intrusion has to overcome the pressure from overlying water plus sediments and puncture the sediment, because it's not brittle. In which case, at depths greater than 3 km, the dyke tip stalls and it spreads out between sediment layers, compacting the underlying layers with its weight. At less depth, when lava does spread out over the sediments, it compacts (and metamorphoses) them. When subaerial (on land) volcanoes or submarine volcanoes erupt, the ground/seafloor around them swells prior to eruption and then subsides after the eruption, a post-eruptive deformation. When a volcano develops, there is subsidence related to the downbowing of the crust as a result of the weight of the volcanic material added to the crust by the active volcano. Counteracting that subsidence, the area surrounding the volcano's subsiding zone is uplifted by material moving downwards and outward from the subsidence zone e.g. as happens with the area around Mauna Loa and Kilauea (they're sinking faster than SL is rising). So by now you can see where this is going. In the genre of quotes about the tides: land goes up, land goes down somewhere else. Along with the calculations in one or both of my previous responses, it would appear that the effect of volcanic activity on sea levels is minimal or, at least, nowhere near as great as you have assumed. And, whatever the effect is, it can be identified and adjusted in the SLR measurements by comparisons among multiple sources e.g. altimetry, tidal gauges and crustal motion measurement.

      Finally, vulcanism is a source of myths. They revolve around or are variations of the 'human activity pales into insignificance beside nature's might' theme. Volcanoes don't put out more carbon dioxide than humans; mid-ocean ridges actually convert more CO2 into carbonates in hydrothermals than the CO2 they release. The annual heat flux from all land-based volcanoes is three orders of magnitude less than (or one-thousandth) that generated by the USA's annual energy use for heating, transportation and manufacturing. And, off topic, taking a Murry-Salby-like position, how do you know that the increase in sea levels isn't causing the vulcanism through some, as yet, unexplained mechanism? Speaking of Murry, my further conversation on this particular topic is terminated.

  14. Oceanic crust does indeed pile up at mid-ocean ridges. However, the ridges are also spreading. The ocean floor slopes away from these ridges, with the relative 'steepness' of the slopes being inversely proportional to the rate of spreading. Combined with the decrease in crust at the subduction zones, the total volume of the ocean basins and thus the sea-level in the absence of any other drivers, remains in a steady state. There was a lot of work in this area from the 60s onward, following the 1961 Nature paper by Robert Dietz.

    1. Graeme M may be assuming that plate tectonics only began in the 60's, following that 1961 Nature paper.

  15. Shorter Billy Bob: "I can't do math, I know f..k all about science... but I doubt that...blah,blah,blah."

    "Now, I don't care a whit whether what I asked has any basis in fact."
    Pretty well sums up your typical denier _ doesn't care about facts, period.

    "I figured you rabid catastrophists would know..."
    Not much of vote of confidence for his idiot denier friends if he comes here to seek information.

    "Has that been factored in?"
    Another typical characteristic of deniers is that they always think that they've spotted something or know something that the experts have missed, such is the hubris of those idiots.

  16. This comment has been removed by a blog administrator.

  17. BB, you really ought to go meet your would-be new best buddy, Spencer Weart. Clearly you're quite intelligent; you don't have to show up in public playing the role of ignorant buffoon.

    OTOH, perhaps your character is intended as a kind of subtle and deeply sarcastic object lesson? The undersea volcanoes gambit is so comical that it's almost too broad but then some folks would say the same of Voltaire's work.

  18. Comments are closed here. Feel free to continue the discussion on this new article on sea level in general.