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Friday, October 24, 2014

Sea level discussion

Sou | 12:14 PM Go to the first of 92 comments. Add a comment


Graeme M (who also comments as Billy Bob) has asked if he could continue the discussion on sea level that began under the article about the new paper from Kurt Lambeck et al (2014). He wrote: "I'd really like to get to the bottom of why I am wrong in this one".

The discussion had shifted to the fact that the oceans are not flat, which is what Graeme M seems to be disputing. I'll start the ball rolling with some of my thoughts together with some of the basic science and observations (measurements).


Height of the sea vs sea level


The height of the sea above the sea floor at any point is of interest to certain groups and individuals. However the discussion was not about the height of the sea at any point in the ocean, it was about sea level - the surface of the sea relative to some reference point.


Sea level vs land level


Sea level is mainly of interest in regard to its relationship to land surfaces. On land, the point at which the land stops and the sea starts will be affected by a number of things, such as an increase or decrease in the volume of water, ocean currents, wind, tides, a vertical shift in the land (subsidence or lifting), and coastal erosion.

There are different ways of expressing sea level.


Global mean sea level and volume of the ocean


Global mean sea level - is a way of monitoring the changes over time in the total volume of water in the ocean. It does not indicate precisely how sea level will change on any particular stretch of coast. The volume is determined by the mass of water and its density. Water expands as it warms (thermal expansion). Water evaporates and condenses, giving fluctuations in the mass of water. Glaciers and rivers flow into the oceans adding to the mass of water. Fresh water is less dense than salty water.

An NOAA chart shows that global sea level has increased by more than 60 mm since 1992:



The sea level has not changed by the same amount everywhere, as this trend map from NOAA illustrates. The map shows the change in sea level globally, since 1993, as measured by satellite altimetry:



Local sea level relative to land


The above map shows the change in sea level from the perspective of the ocean itself. To see it from the perspective of land, there are tide gauges and instruments to measure changes in the height of the land surface. These instruments monitor the change in sea level relative to the land, as well as determining the extent to which changes over time are caused by changes in the height of the local sea or changes in the the height of the local land surface (is the land rising or falling or is the sea rising or falling or both).

Below is a link to chart showing sea level changes from the perspective of land at different places around the world:

http://tidesandcurrents.noaa.gov/sltrends/sltrends.html.


The above is an introduction. Comments are welcome on the topic of sea level.

92 comments :

  1. A couple of years ago Rob Painting at SkepticalScience wrote a series of blogs on sea level rise, starting with the attempt by North Carolina lawmakers to legislate SLR out of existence, and continuing on to explain why sea level isn't level. As a science-deficient person, I found these fascinating and educational:

    http://www.skepticalscience.com/North-Carolina-Lawmakers-Turning-a-Blind-Eye-to-Sea-Level-Reality.html

    http://www.skepticalscience.com/Sea-Level-Isnt-Level-This-Elastic-Earth.html

    http://www.skepticalscience.com/Sea-Level-Isnt-Level-Ocean-Siphoning-Levered-Continents-and-the-Holocene-Sea-Level-Highstand.html

    http://www.skepticalscience.com/Jerry-Mitrovica-Current-Sea-Level-Rise-is-Anomalous-Weve-Seen-Nothing-like-it-for-the-last-10000-Years.html

    FLwolverine

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    1. I tried for a first, and then a second, but I'm just too slow. However, I still want to get in something reverential.

      Mitrovica's 2011 video, "the Fingerprints of Sea Level Change" is second only to Alley's Control Knob video, it its ability to simplify a complicated topic..

      I'm still waiting for that explanation that simplifies the differences between the different kinds of Climate Sensitivity.

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    2. This is an OK introduction to Climate Sensitivity and it's complications

      https://www.youtube.com/watch?v=aqmw46Q4LdE

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    3. three cheers SOF, but you forgot something
      Jerry Mitrovica, Harvard University
      SacklerColloquia
      https://www.youtube.com/watch?v=RhdY-ZezK7w
      Uploaded on May 18, 2011
      The Fingerprints of Sea Level Change

      This meeting was held March 31-April 2, 2011 at the AAAS Auditorium, in Washington, D.C. and was organized by Rita Colwell, Christopher Field, Jeffrey Shaman, and Susan Solomon

      Meeting Overview
      Climate science is addressing issues that require an increasingly interdisciplinary perspective, posing new challenges to scientists and to the organization and support of this science. Like other interdisciplinary activities, recognition and support of interdisciplinary climate science by the broader scientific community—including university and government administrators, journal editors and reviewers, and funding agencies—is advancing slowly. Often it is easier to recognize ideas that would represent major advances within a discipline, than ideas that would provide major advances but cut across multiple disciplinary foundations. This circumstance poses a challenge to interdisciplinary research and may slow interdisciplinary scientific advances. Such issues are of particular significance for studies of climate impacts, which may, for example,represent linkages between physical and social science, as well as feedbacks among physical, chemical and biological systems.
      ~ ~ ~

      cheers

      Delete
  2. Graeme M, if you don't understand why I disagree I'm not sure I can do much more to help you than point you at my previous extensive comments. There's more than one reason I disagree (depending on what the proposition is) and you only need to understand any one of them to understand at least some of the disagreement.

    If you want to try again, I reckon the easiest way to unlock the enigma is to focus only on this:

    1) If I understand it right, your argument asserts that over a long enough term sea level rises at ALL coastal locations around the globe MUST ALWAYS be very similar. This is because you assert that "on coastlines these two levels" (the geoid or gravitational equipotential surface, and the long term average sea level at the coast) "are pretty much the same (I think within 100mm or less though I have no references for that)."

    So correct me if I'm wrong, but that means that you're asserting that any two coastal average sea levels from anywhere around the world (corrected for land movements) and over a sufficiently long period (for some definition of "sufficiently long") must both be within (say) +/- 100mm of the actual geoid.

    2) SD observes at least one location around the world where he reckons sea level at a coastal location has not measurably risen in a timeframe exceeding the 21 years shown on Sou's figures. Let's call it a "rise" of 0 mm for the sake of argument.

    3) I observe at least one location around the world where sea level at a coastal location has risen by a lot more than 100mm in a timeframe of 21 years, e.g. see the NW of Australia in the figure Sou posted where sea level rise since 1993 has been 20cm or more in 21 years. And since SD is claiming no rise in 60+ years we could look in the tide gauge data sets over 60 years and almost certainly find at least one that has risen a fair bit more than 20cm in 60 years.

    4) By application of argument (1) to data point (2), one MUST conclude that sea level rise ON ALL COASTS AROUND THE WORLD in that kind of timeframe has been 0mm +/- the 100mm difference from the geoid allowed by the argument.

    5) By application of argument (1) to data point (3), one MUST conclude that sea level rise ON ALL COASTS AROUND THE WORLD in that kind of timeframe has been 200mm +/- the 100mm difference from the geoid allowed by the argument.

    6) But both (4) and (5) cannot be true, so something is wrong with this argument.

    Is (1) a fair representation of your argument?

    Assuming it is, do you disagree with this 6 point argument? If so, why? If not, what needs to change to eliminate the conclusion that "something is wrong with this [6 point] argument"?

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  3. https://www.youtube.com/watch?v=RhdY-ZezK7w

    Obviously Graeme and Billy Bob ~both~ managed to miss this video when it was put up before, or missed every single point that Jerry Mitrovica made about sea level and gravity.

    This is the chance to watch it all again. Maybe watch it through again after getting the general idea.

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  4. Sou, one thing you left out of your list of things that affect sea level relative to land is gravity. It turns out that the gravitational attraction of the Antarctic ice sheet is enough to raise sea levels around the continent. I'm not sure but a range of 5-20 feet (1.5-6 meters) sticks in my mind. That also applies to the Greenland ice sheet and the mountains along the west coast of the Americas and I'm sure elsewhere. It blew me away when I learned of it.

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  5. Well, I am impressed. Thank you for the indulgence Sou. I know your blog is not a classroom, so I appreciate it.

    I am often pressed for time and find it hard to get the opportunity to read as much as I like - hence this discussion has been done on the strength of my recollection of the thread at Deltoid. Today though I managed to do some further research into the geoid/MSL thing, and I don't think I've changed my mind. So, while I think I grasp the concepts, I must be missing somethng about its application.

    I will try to read this post more carefully tonight and will even look at Adelady's video.

    Just quickly though - Lotharsson, I don't think you've captured what I am contending. Would it help if we went by baby steps, that way you might be able to see where I am going off-track? And please don't get hung up on my language as I don't always know the correct terminology. It's the concepts that count.

    My first point then.

    I understand that a fluid will 'seek equilibrium' with the local gravity field. That is, a container of fluid placed on my bench at home will settle to a state where the surface is level, or flat, with respect to the local gravitational attraction. That is, its surface will be perpendicular to the direction of gravitational attraction. Ignoring things like surface tension, size of container etc. This is the reason that a spirit level works.

    The ocean is a fluid. If the earth were a perfect sphere and there were no currents, waves, or tides etc, the surface of the ocean would also settle into a state of equilibrium. On average, the sea surface at Point A on the equator would be exactly perpendicular to the direction of gravitational attraction. It would be level. Equally, a Point B on the equator exactly opposite Point A, that is on the other side of the earth, would also be exactly level. I am not talking height, or shape, I just mean level at each point, in relation to gravity.

    Do we agree on this?

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    1. When you blow on your coffee, does the level rise slightly on the opposite side of the cup?

      Does it get lower on the near side?

      How might this apply to an ocean basin and major atmospheric circulation patterns?

      Does warm water expand? Does cold water contract? How might this affect coastal sea level?

      What about gyres?

      Etc.

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    2. >"If the earth were a perfect sphere and there were no currents, waves, or tides etc, the surface of the ocean would also settle into a state of equilibrium"

      No, it wouldn't.

      First - earth is in constant motion, it is not still. It rotates on an axis and revolves in an orbit. This movement exerts force, even leaving aside the gravitational force of the moon, the forces operating within the atmosphere, the forces operating within the ocean itself, the forces operating between the ocean and the atmosphere, the forces operating with of the sea butting against land masses (continents, continental shelves, even islands), and the forces operating fresh water flows into the ocean, changing the dynamics of temperature, density etc.

      That's just off the top of my head.

      Thing is, the water in the ocean is *not* like the water in a glass, or a sink or a bath or a small still pond.

      Also, as you say, Earth is not a perfect sphere.

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    3. Graeme, NOAA has some tutorials on the ocean, which would be useful background reading if you are to understand factors affecting sea level. They are short articles written for the lay person (non-scientist). Below is a link to the first page:

      http://oceanservice.noaa.gov/education/tutorial_currents/welcome.html

      The sidebar lists short tutorials on each of:

      Tidal Currents 1 and tidal currents 2

      Coastal Currents - be sure to click on each of the four tabs at the top of the article.

      Surface Ocean Currents - including the coriolis effect, trade winds, boundary currents and the Ekman spiral

      The Global Conveyor Belt - including thermohaline circulation, the global conveyor belt, and effects of climate change.

      How Are Currents Measured? - with a number of tabs at the top.

      How Currents Affect Our Lives?

      Some references.

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    4. Sou and BBD, let's not get this sub-thread off on to multiple tracks! Let me have a go at working through it starting from the way Graeme thinks about it and see if that leads to some progress. I think he's put up a useful starting point.

      Delete
    5. Graeme, agreement or disagreement depends on the precision with which we are working (and conflating different degrees of precision has been one of the core problems in the argument to date), so as your thought experiment currently stands I can't simply agree (or disagree) with it! However I think with more work on it we can reach agreement.

      Let me explain using your example why precision matters when checking for agreement. Consider the container on the bench scenario. First, let me try and refine the description you gave to (hopefully) more precisely capture your point. Would you agree if I tried to restate it as:

      "If water in a container is subject to a set of forces that don't change over time until it reaches an equilibrium state, then the water surface at each point will be perpendicular to the gravitational force at that surface point"?

      If so, then here's the rub:

      A) If we are are happy with a relatively low precision level in the description of the outcome, then I agree.

      B) If we are require a relatively high precision level, then I must often disagree depending on the scenario, and I would often have to ask you to specify more details before I could even tell you whether I agree or disagree!

      For low precision analysis like (A), we know from existing physics that gravity is the dominant effect in that scenario (i.e. the other forces acting don't modify the outcome within the low level of precision required). Hence while your description of the outcome ignores all of the other forces that's OK here because we know (from that other work) that including them doesn't make a big enough change at this level of precision. Great!

      But if we're doing high precision analysis like (B), then it is not correct to assert or assume that gravity is the only force that matters for the precision required. As just one example of another force that must be accounted for when the required precision is high enough (even in the really simple static container-on-a-bench scenario) the well known "capillary action" affects the water surface shape and it can cause a meniscus to form. When there is a meniscus the water surface is obviously NOT perpendicular to the gravitational field over the entire container - in fact the perpendicular to the surface can be quite a long way off the vertical axis (see the pictures), even almost reaching the horizontal axis in some cases!

      [...continued in next comment...]

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    6. [...continued...]

      Hence, strictly speaking, saying water seeks equilibrium with the local gravitational field is incorrect (or incomplete if you prefer). A more description is:

      "If water in a container is subject to a set of forces that don't change over time until it reaches an equilibrium state, then the water surface at each point will be in equilibrium with the sum of the forces acting on the water at each surface point".

      In other words, saying:

      "If water in a container is subject to a set of forces that don't change over time until it reaches an equilibrium state, then the water surface at each point will be perpendicular to the gravitational force at that surface point"

      is an approximation! And it can only be a valid approximation in circumstances where the forces unaccounted for by the approximation have impacts small enough to be ignored, for the required level of precision.

      But that raises another question - how do we know whether or not such an approximation is good enough for the purpose at hand?

      Well, you have to do some kind of assessment of either:

      (a) how well the approximation matches reality, which you can only find out by going out and measuring reality to sufficient precision (so you can't simply assert that it matches well enough) and showing that the discrepancy is small enough for your purpose (e.g. for the claims you are making), or

      (b) the size of the impact of all the known forces (which you can only find out by understanding those forces and how they affect water), so that you can remove analysis of some forces whose impacts are small enough to ignore at the level of precision required.

      In other words, you can't simply assert that "this approximation is good enough for this purpose", you either have to show through lots of measurement that it always appears to be good enough, or you have to work backwards from the most complete description we have to the approximation demonstrating that what you threw out of the complete description is justified at the given precision level. If your approximation isn't known to be good enough for your argument's purpose, then it cannot be used to support your argument.

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    7. Holy cow! We didn't get far did we. Lotharsson, all I am asking for is agreement on a general principle - that fluids seek to be level. Of course there can be all sorts of other forces at work. But, generally speaking - in my kitchen at least - a container of water on the bench will have a level surface with level being perpendicular to the direction of gravitational attraction. If I tilt my container, the surface will remain level, it won't follow the cup.

      Do you agree with the general principle?

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    8. We didn't get far did we.

      To be more accurate you did not get far. And you did not back up to try and reach some common understanding. Classic problem with people who will discuss on their terms only.

      Lotharsson laid out in some detail why he does not think your statement is sufficient or complete. In two different ways!

      Back up a bit to what he has said and see if you can establish where you part company. What you do not seem to get is that he is being more precise than you and more careful with the words and definitions to use. In a (so far futile) attempt to avoid misunderstandings.

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    9. "Lotharsson, all I am asking for is agreement on a general principle - that fluids seek to be level"

      Except that's wrong in two important ways, one of which has been pointed out several times.

      1) I can come to your house with a container, pour some water in it and point you to the resulting surface which is clearly non-level, as that Wiki page I linked to illustrates. Are you actually denying that menisci exist, and anyone can create one on their own kitchen bench?!

      2) More importantly, it's an incomplete description of the physics at work and thus by definition it cannot be a general principle. "General principle" means that the principle applies to all situations.

      The correct general principle here is "water that reaches equilibrium does so with respect to all forces acting upon it". This principle applies to ALL situations where water is in an equilibrium state.

      Do you agree with that?

      If you do, then we can move on to seeking agreement on a specific "principle" that looks somewhat like your "general principle".

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    10. Ignoring the effects of ocean currents, winds, isostatic rebound, geographic features, etc., this short video looks at the effect that variations in gravity have on sea level from around the 1min 15 sec to 2 min 45 sec marks. (The last 30 seconds are largely an advertisement for the sponsor firm who funded the video.) All in all it's pitched at a easy to understand level. One note: the video uses the term 'centrifugal effect', which is better than 'centrifugal force', but is more correctly known as 'centrifugal reaction' which sets off a minor skirmish among some 'purists' who've posted comments below the video.

      Oh! Based on the physics, if your glass of water is close to a large mountain range, or for that matter a large building, or is to one side of massive underground metallic/non-metallic ore body, its surface won't be horizontal. Not that you'll be able to see it but, with the right equipment, it could be measured even if it was off by nanometres.

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    11. Lotharsson

      Sou and BBD, let's not get this sub-thread off on to multiple tracks! Let me have a go at working through it starting from the way Graeme thinks about it and see if that leads to some progress. I think he's put up a useful starting point.

      Sorry, sorry :-)

      Following.

      Delete
    12. Graeme M - I'm not sure that I have ever seen it before on a blog thread but Lotharsson just provided a DH7 level entry to the discussion. Unfortunately you did not recognize this. Lotharsson actually improved your argument and then explained quite clearly why it is incorrect. You seem to want to get Lotharsson to agree to your premise that fluid surfaces equilibrate themselves perpendicular to local gravity as a general principle. However, as Lotharsson has very clearly explained, this is only precisely correct under special circumstances. I guess the only way to more clearly demonstrate the point is with a full solution to an idealized problem that provides a counterexample to your assertion.

      Lotharsson - Unfortunately it does not appear that Graeme M has the background in mechanics to grasp your explanation.

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    13. Thanks Anonymous. (Not sure what DH7 level means but it reads like a compliment ;-)

      I have been hoping that anyone could grasp one of the problems regardless of background in mechanics by looking at counter examples such as a container where the liquid surface has a meniscus. Otherwise I'm getting a bit short of ideas for explanatory strategies, although I still have an analogy to common experience to try...

      Delete
    14. Yes, it was a compliment. I usually lack the patience to even try such responses. I had though about attempting a solution of a simple problem and posting it, but I can't think of any problems comprehensible to someone without knowledge of mechanics.

      Delete
  6. @Graeme M sock.

    How about this? First, state your hypothesis. Then provide evidence to support it (i.e.. scientific papers).

    If you can't even do this, then don't bother continuing.

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  7. A lump of rock 3000 miles across and 250,000 miles away can cause sea level to increase and decrease by several metres twice a day.

    Surely this is the clearest indication that gravity and other forces can vary local sea level!

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    1. Not only that but it varies the local land level too. Now that adds another factor to change of sea level.

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  8. "global sea level has increased by more than 60 mm since 1992"

    60 mm in that period of time is a lot. To me sea level rise is the line of evidence that proves Global Warming beyond reasonable doubt.

    Short of deniers claiming instrumentation inaccuracies or a conspiracy, I can't see them arguing this one.

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  9. Graeme " ...a container of water on the bench will have a level surface with level being perpendicular to the direction of gravitational attraction."

    Yup. Now see if you can find some information about the relative gravitational effects of massive things like continents and ice sheets and oceans.

    I strongly - repeat strongly - advise you to watch that Jerry Mitrovica video. If you don't want to watch all of it, start at about the 14 minute mark. He explains all the things that you're not taking into account. Like the huge mass of Greenland or East Antarctica. There's also a really, really interesting comment from him about the work of one of his students on the expected uplift of West Antarctica when the weight of the ice sheet is removed by melt.

    One example in the video. What would you expect to happen if the Greenland ice sheet melted all at once? Do you think the sea level at the coast of Greenland or Scotland to rise or fall with that huge quantity of water moving from land to ocean? The answer isn't as straightforward as most people might think.


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    1. "if I were standing next to the Greenland ice-sheet and it catastrophically collapsed sea level would drop by 100 metres. This is not controversial!" at 15:30

      Wow! Did I hear that right? Rather blows the idea of liquids being level into next week.


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    2. That change in sea level would be due to the removal of the ice mass on Greenland, which changes the gravitational field and hence the geoid surface.

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  10. This is very difficult, and I am not sure why it is so. Maybe my language is clouding the issue.

    I understand very well what Lotharsson is saying and I understand all of those other matters. What I am trying get agreement on is the general idea if you will about how a fluid acts on the earth's surface.

    There are two large forces at work - gravity and pressure. Fluids seek, in the absence of other forces, to be level. It's why a U-tube of fluid will have both sides level, in the absence of competing forces. I can level something using that U-tube idea - if I use a long enough tube, I can level objects quite far apart, relatively speaking.

    Of course I understand all of those things such as meniscus and so on, but these are micro factors that don't affect the general idea.

    Fluids, on the earth's surface, tend to seek to be level.

    Why is that such a difficult concept to agree on?

    Taking your example of the meniscus, that is an example of the local forces of the fluid overcoming the effects of gravity and pressure at a very small scale. If my tube were very very wide, the effects of the meniscus overall would be much diminished. In the case of the narrow measuring device at that Wiki page, they actually tell you that the level shown, being affected by those local forces, needs to be adjusted to provide an accurate reading. They calibrate the scale shown to allow for those effects, so that if you line up the bottom of the meniscus you get a correct reading. The core fact remains - pressure and gravity cause the fluid to be level.

    If I rock my container on my bench, the level inside will vary. Of course, that's a trivial observation. We can all see that. But if I stop rocking it, what configuration does it adopt? All stuck to the side of my container? Creeping up one side? A surface level of 45 degrees? No. In most cases, the vast majority of cases for containers of fluid, eg cups of coffee at the cafe, the surface is level.

    Do you agree?

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    1. This is very difficult, and I am not sure why it is so.

      Just what I was thinking.

      There are two large forces at work - gravity and pressure. Fluids seek, in the absence of other forces, to be level. It's why a U-tube of fluid will have both sides level, in the absence of competing forces. I can level something using that U-tube idea - if I use a long enough tube, I can level objects quite far apart, relatively speaking.

      One of your problems is that you are not being explicit about your assumptions. Even if gravity and pressure were the only forces at work you are implicitly assuming that they are uniform on an oceanic scale. The reason your U-tube works is that these forces are reasonably uniform locally. Your intuition about how fluids find a level is a good approximation at a small scale but you can't simply scale that up over the breadth of the oceans without making assumptions that don't match reality.

      Delete
    2. Bob, in that comment I wasn't wanting to introduce sea level as such, I just wanted agreement on the basic fact of fluids seeking to be level.

      This discussion overall may cover two ideas. One is the idea that the sea's surface is essentially level insofar as measurements of MSL are concerned. The second is what that means for measuring sea level rise.

      Initially then, I thought we could agree that fluids will tend to be level on the earth's surface, in the absence of other perturbing forces. I thought that was quite uncontroversial, it's what you learn when you do any reading on the subject. I am not trying to say that the surface is flat and level to the value of micrometres. I am just saying that fluids seek to be level in the generally accepted sense of 'level'.

      Heck, just go do it. Fill a bucket with water, let it rest for a minute, and tell me the surface configuration. If it's NOT generally level, send me a photo. Get 5 other buckets of different sizes and fill them to varying levels, same thing. What the heck is so hard about this idea?

      If we can't agree to this simple and well understood concept then I have no idea where to go from here.

      Do fluids on earth's surface tend to seek to be level?

      Delete
    3. Graeme, as long as you ignore what everyone else has written and keep pushing stuff like that, you'll be hard-pressed to find anyone willing to engage in discussion with you. Heck. Engagement isn't possible. You don't allow any.

      You wrote:"This discussion overall may cover two ideas. One is the idea that the sea's surface is essentially level insofar as measurements of MSL are concerned."

      As shown in the article above, and in the comments from various people, and in the references to papers and videos that have been posted. The above statement is way wrong. The sea's surface is not essentially level insofar as measurements of mean sea level are concerned.

      Therefore your second sentence: "The second is what that means for measuring sea level rise." is irrelevant and meaningless.

      Look at the chart and map in the article above. The change in global mean sea level has been ~60mm since 1993, but the change in different parts of the ocean has changed variously +200 mm in some parts and -200 mm in others. That does not denote "essentially level". Look at the tidal changes in the link in the main article. Look at the Jerry Mitrovica video that Adelady and others have suggested. Read what Lotharsson wrote here and in the other thread.

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    4. Bob, in that comment I wasn't wanting to introduce sea level as such, I just wanted agreement on the basic fact of fluids seeking to be level.

      OK, let's leave sea levels out of it. But it is not a 'basic fact' that fluids seek to be level. The basic facts are the physics of how fluids flow under the influence of forces acting on them. A consequence of the physics is that if you have uniform gravity and pressure in the region that you are considering the surface of the fluid then the surface will tend to be level.

      Do fluids on earth's surface tend to seek to be level?

      See above. The answer is yes if you mean a constrained situation such as your bucket example, but no if you are trying to state it as a general principle in the absence of clarifying the assumptions you are making.

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    5. Perhaps the problem is that you don't understand that your question is poorly defined. You don't define what you mean by "level" and it's not a trivial thing to define unambiguously.

      It is true that in a uniform gravitational field, the surface of a homogenous fluid will (ignoring the meniscus at the edges) be very close to a perfectly flat plane perpendicular to the direction of the grav field.

      But *none* of those conditions are true, at any time, anywhere on Earth. So it's a most a thought experiment. You keep mixing up a thought experiment with the real world (as your comments about taking photos of buckets makes clear) and then complaining when people tell you you're wrong.

      So the answer to your last question: "Do fluids on the earth's surface tend to seek to be level?" is no. Once you accept that, and understand why, you might start to make progress.

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    6. *Seek*, sure, but the earth's surface is not level, leading to variations in gravity, so while they may seek it they won't find it, except locally. For that matter, if you measured the fluid surface across your U-tube with sufficient accuracy, you would find it too to not be perfectly level.

      Note that over geologic time land has some properties of a fluid, but although it too would like to be level, and eventually would be if gravity were the only influence (assuming also some minimal erosional process, I suppose), it isn't.

      Perhaps the surface of a neutron star is as close as one could come to ideal levelness, but I suspect that even there bumps happen.

      You can discuss a spherical cow, usefully even, without imagining that it exists literally.

      So sea "level" isn't level at all, but is a local or global average of a bumpy and time-varying surface.

      Disagree with any of that?

      So now, what was your original question?

      Is it still this?:

      "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."

      If so, consider e.g. the current changes in the ACC driven by the expansion of the tropics. That'a a large, long-term effect with obvious effects on local sea levels all around the Southern Ocean. Similar effects can be expected all over the oceans.

      Another point is that as sea level rises the gravity exerted by the oceans increases unevenly (more toward the middle of the oceans), which will also make the distribution of sea level rise uneven.

      Finally, increasing depth will itself change currents, again changing local sea levels.

      So rather than being surprised, we should expect some pretty big variations in local SLR.

      Delete
    7. "This is very difficult, and I am not sure why it is so."

      Largely because:

      1) You aren't dealing with the key distinctions being made by people who are responding to your argument with a more precise analysis, nor the reasons given for those distinctions being important here.

      Simply handwaving those distinctions away or declaring them unimportant here does not invalidate objections made on that basis. Restating your case without explaining why you think the objections don't apply doesn't invalidate them either, it just makes the whole process more difficult.

      2) You refuse to accept the level of agreement that has been given to you, let alone deal with the reasons why full agreement is not forthcoming.

      If you don't like the difference between the level of agreement you seek and the level of agreement observed you have to engage with the reasons given for the difference. (Hmmmm, kinda like engaging with the reasons given for the difference between the level you say water seeks, and the levels of seawater actually observed...?)

      Also, whenever the going gets tough in one sub-thread you have a habit of starting another one instead ;-) That's always going to make it more difficult.

      Delete
    8. "I understand very well what Lotharsson is saying..."

      I'm not at all convinced that you do! If you do you'll be able to point out where you disagree with any of it and why. So far you have quite conspicuously and obviously avoided doing so.

      For example, you haven't said whether or not you agree with my yes-this-is-actually-a general principle, let alone point out a good reason to disagree with anything I have said (and you appear to have abandoned that sub-thread). You have ridden roughshod over several key points which, if you understood them, reveal several different reasons why I must reject your "general principle" unless appropriate qualifications are added (qualifications that I offered!)

      Feel free to restate what I said and explain where the difference between our positions lies in order to demonstrate that you understand (and then focus on the differences in order to advance the discussion).

      Delete
    9. "What I am trying get agreement on is the general idea if you will about how a fluid acts on the earth's surface."

      No, you quite clearly are not. The key giveaway is that you already have agreement but with added caveats that prevent it being misapplied and you have refused to accept that form of agreement.

      In other words, you are trying to get inappropriately unqualified agreement on an approximation of how fluid acts on the earth. And you're doing that in order to mis-apply the approximation (whether consciously or unconsciously) and the audience here sees right through that.

      Delete
    10. "The core fact remains - pressure and gravity cause the fluid to be level."

      Wait, what?! You've JUST FINISHED AGREEING IT IS NOT LEVEL, AND NOW YOU ARE SAYING IT IS!!!

      And you've spent all this time saying that IN GENERAL GRAVITY ALONE MATTERS AT EQUILIBRIUM and now you are citing the effects of PRESSURE too?

      You seem to be arguing with yourself now, but weirdly it might indicate a modicum of progress ;-)

      Delete
    11. Lotharsson, I'll have one last shot at this because I just can't think of a way to describe a well known effect in a way you'll just agree with. I *think* you are agreeing with me but your elaborate, verbose responses make it difficult. I'm not being critical, I just can't follow you.

      I am not trying to make a statement in a perfectly defined and constrained scientific way about something. I simply said that on average, a fluid seeks to be level at rest. That seems to be right to me even though I suppose my use of the language is imprecise. But all the other responses keep throwing up aspects to that idea that are simply distractions.

      I will therefore ignore all other comments and simply follow this one thread with you. Please, at this point I am not discussing sea level rise or anything like that. I am starting at the bottom to try to define what SD meant by his billiard table principle, nothing more.

      So. let us discuss water only. Water in its typical form on the surface of the earth at say 20C constantly. What is the underlying idea/principle/concept/effect/whatever term makes sense to you that makes the water in a cup, or a bucket, or a tank or a dam or a lake be generally 'level? Please explain in as few words as possible, in the simplest possible way.

      Delete
    12. "...I just can't follow you."

      OK, but this suggests a major problem. The details matter. Insisting on simplification because you can't understand the important details is like the drunk at night searching for his car keys under the streetlight 100m away from where he dropped them because at least here there's some light. He can see something, but by definition he can't possibly see what he needs to see.

      Anyway, let's see if we can make progress.

      "What is the underlying idea/principle/concept/effect/whatever term makes sense to you that makes the water in a cup, or a bucket, or a tank or a dam or a lake be generally 'level?"

      As previously stated it is in 2 parts.

      1) The general principle which applies everywhere and always:

      "Water that reaches equilibrium does so with respect to the sum of the forces acting upon each water molecule."

      In other words the shape of the surface for "water at rest" depends on all the forces and how that sum varies across the body of water.

      2) The specific application of that principle under certain conditions, and only under those conditions:

      "If that sum of forces is (close enough to) constant across a water-filled region, then the resulting equilibrium distribution of water (a.k.a. "the shape of the water surface at rest") will be (close enough to) "level" (i.e. perpendicular to the direction of the sum of forces)."

      (Even that is necessarily a simplification that I won't go in to, because making it more correct will only cause confusion.)

      Water "at rest" in a cup or a dam or a tank or a bucket in the situations you're thinking of meets the conditions in (2). The sum of forces (including but not restricted to gravity) is close to constant across the body of water, and the result is a surface that is close to level.

      Delete
    13. So you agree that as a broad principle, in most circumstances, water will seek to be level at rest. It may be influenced by other factors that result in its real surface NOT being level, but underlying that is a tendency to be level. If I fill a dam full of water and it generally meets condition 2, it will be 'level'

      If I then measure that surface over time, perhaps via some sort of altimetry or surveying capability, will the average surface more closely approximate level?

      Delete
    14. "So you agree that as a broad principle, in most circumstances, water will seek to be level at rest."

      No!

      A) You're talking about my (2) above. That is a quite narrowly applicable "principle", as I took some care to point out, so labelling it "broad" or "applicable to most circumstances" are both dubious.

      But more importantly "broad" and "most circumstances" are not even useful to this discussion. Since (2) is a "principle" that applies in certain circumstances, when we seek to apply it somewhere we don't care about how many circumstances we can think of that it applies to ("broadness" or "most circumstances"). We only care about whether or not it applies to these circumstances. That question is independent of "broadness" or "mostness".

      Imagine I said "it's a broad principle that most cars today rely on a combustion engine". I'd probably get agreement from most people as this is a genuinely broad principle right now. Imagine I then said "That means that your own car relies on a combustion engine". You'd see a lot of objections because the engine type of a specific vehicle is not determined by the fact that most vehicles have a combustion engine - as the owner of any pure electric vehicle can tell you. However, this kind of fallacy appears to be required by your argument!

      B) You are now talking about a definition of "level" that is perpendicular to just gravity, not perpendicular to the sum of forces acting on the water. That brings in an additional assumption that further narrows the applicability of the principle. If you want me to refine what I said in (2) to be closer to what you just said how about this:

      3) If gravity dominates the sum of forces acting on a body of water (i.e. "gravity is much larger than all the other forces combined"), and if gravity is (close enough to) constant across the water-filled region, then the shape of the water surface at rest will be (close enough to) "level" with respect to gravity".

      Now we have something that is hopefully quite close to what you say, but which includes the qualifications that are necessary before I can accept it. If we agree on that we can move on to see if the argument(s) that you make by trying to apply it respect that necessary qualifications.

      Delete
    15. You have muddled things up now.

      You stated, quite clearly, that:

      1. The surface of a body of water responds to the sum of forces on its surface. It's shape will be a product of those summed forces. I agree.

      2. That if those summed forces are constant, the shape of the surface at rest will be perpendicular to the direction of those summed forces. I agree.

      'At rest' means that we have removed from the equation all forces of greater strength than gravity. As we remove forces, the water will more and more approximate a state of 'levelness' to gravity. Gravity IS a constant force and it is one we cannot remove from the equation. Its vector may vary minutely due to topography, but it is largely one direction - down.

      Once we have removed as many forces as we can, the remaining forces are quite small in comparison to gravity. The direction of gravity, and the direction of the summed forces, is pretty much the same.

      Water at rest will be level on earth's surface, as required by your 1 and 2 above. The addition of other forces simply acts to perturb the surface away from level. As we subtract those forces, water returns to its level state.

      Overwhelmingly, the natural shape of the surface of a body of water on earth's surface is to be perpendicular to local gravity - that is, to be level. All other forces when they occur simply combine to change that shape, exactly as required by your 1 and 2.

      You even state this in your most recent comment at 3) when you observe that if gravity is dominant and constant the surface will be level in respect to gravity. Exactly.

      Water seeks to be level.

      Delete
    16. Lotharsson, Jonathon Gradie below has made a very good observation. This thread is simply messing up Sou's blog. Let us stop here as we aren't getting anywhere and it is counterproductive for the blog's visitors.

      Delete
    17. "You have muddled things up now"

      No, you falsely thought I was agreeing with you. Pointing out that is false is not "muddling things up", it is attempting to clear things up.

      "'At rest' means that we have removed from the equation all forces of greater strength than gravity."

      Woah! That's not what "at rest" means to anyone else! It essentially means not moving or changing. There are any number of situations where forces stronger than gravity are obviously at work but the substance in question is not moving or changing. It really really helps if you use the correct terms.

      "As we remove forces, the water will more and more approximate a state of 'levelness' to gravity."

      Yes, if we're doing that as a thought experiment - but then we must also acknowledge that the resulting thought experiment tells us less and less about the sea in the real world!

      "Gravity IS a constant force..."

      Not entirely. AGAIN it depends on how precise you need to be (for the problem at hand).

      As one example, if water density in one part of the sea changes, it changes gravity in that part of the sea. As continents move, they (slowly) change gravity. As magma flows under the crust - without even erupting - it changes the distribution of mass in the earth, which changes gravity.

      It's a matter of degree. You frequently think in binary terms ("it totally is" vs "it totally isn't") when it really matters how much it is. And you seek to get agreement on a simplified model that eliminates certain factors before you apply that model to your problem, which is fallacious! You have to show that the effect of simplifying the model is small enough for your scenario before you apply it, not assume that it is.

      "Water at rest will be level on earth's surface, as required by your 1 and 2 above."

      That's not true for (1). The sum of forces might be unchanging but that doesn't mean it's the same everywhere. If it did mean that I wouldn't have needed to define (2).

      And strictly speaking that's not true for (2). The sum of forces can be constant across the body of water, but the summed forces may not point in the direction that gravity points - in which case the water will be "at rest" but NOT level with respect to gravity. That's why I worded (2) the way I did, and then went on to define (3). If you say "water at rest under scenario (3) will be level on the earth's surface" I will happily agree.

      What you can say is that in many cases for water observed to be (close enough to being) "at rest", that it's (close enough to) level with respect to gravity. But you CANNOT say that it must always be like that because that's wrong. And as always when you're talking about real world observations rather than thought experiments it's a matter of degree - is it close enough to what you said for the question at hand or not? You can't simply declare that it MUST be close enough because you cling to a simplified principle, you have to demonstrate that it is.

      You are quite determined to wave away effects and complexities that are quite probably significant when discussing sea level rise. Furthermore, you clearly want people to accept the waving away as a general principle applicable everywhere - or at least as applicable to sea level, without having to go through the bother of showing that the simplifications you make don't affect the analysis of sea level too much. You can't do that because it's fallacious. It remains fallacious no matter how many times you try to get someone to agree to do it, and it will remain fallacious even if someone agrees to it. You might want to try a different argument, or actually take on board the feedback provided and try and fix this one.

      Delete
    18. "Water seeks to be level."

      No.

      A liquid will reach an equilibrium that is the sum total of the forces acting upon it. It's that simple.

      Your insistence on a gotcha-type of cornering is nothing more than imagining only Steve Bloom's and John Mashey's spherical cows. Reality is much more complicated, as Lotharsson summarised, and your attempt to limit a liquid's theoretical response to gravity alone is irrelevant to any argument about global sea level. If nothing else, you are working on a model of water as a fluid that ignores that the atmosphere is also a fluid, and hence that the topography of the surface of the seas is the sum of the distribution of the single overall system that is both water and air. And we all know that the planet's atmosphere is hardly static...

      "Level" is a naïve concept, and a seriously misleading one in attempting to grasp the profoud ignorance that underlay Spangled Drongo's countless errors of understanding on those lengthy Deltoid threads. Drongo had nothing substantive to offer the sea level debate because he ignored so many parameters germane to the discussion that everything he said was rendered irrelevant.

      You seem determined to follow exactly in his footsteps.

      Delete
    19. "Water seeks to be level"

      Well what do the OBSERVATIONS say.

      "The ocean surface has highs and lows, similar to the hills and valleys of Earth's land surface depicted on a topographic map. These variations, called ocean surface topography (or sea surface topography), also dynamic topography, are mapped using measurements of sea surface height relative to Earth's geoid. Earth's geoid is a calculated surface of equal gravitational potential energy and represents the shape the sea surface would be if the ocean were not in motion.

      The height variations of ocean surface topography can be as much as two meters and are influenced by ocean circulation, ocean temperature, and salinity."
      http://en.wikipedia.org/wiki/Ocean_surface_topography

      So that's a big fat NO.

      So the discussion should have ended there, but were the FACTS and OBSERVATIONS accepted. NO. They were denied and denied and denied and denied and denied.

      So given that the ocean is in fact not level, measurement of sea level at a SINGLE location to determine sea level rise is totally and utterly useless. That's where the M in GMSL comes into play. It stands for mean, or average, and to determine a good average requires many data points, over a long period of time.

      But did Graeme M incorporate this simple FACT into his brain. NO.

      "Your summary of my simple model is simply NOT what I said"

      Why don't you state what your model is then in the first place, instead of skirting around it. So if my interpretation of your model is incorrect, then WHAT is your model? State it in ONE sentence. I asked you to do this but you refused/ignored me. It is a very simple request.

      Delete
    20. DJ - Graeme M/Billy Bob won't be commenting here any more.

      Delete
  11. "Holy cow! "
    Yes, assume the spherical cow.

    ReplyDelete
  12. You have a manometer filled with two immiscible fluids, water on one side and oil on the other side. Why are the two fluid surfaces NOT at the same elevation?

    You have a magic manometer with infinite specific bulk modulus and infinite specific elastic modulus and infinite specific strength (basically the same thing as all are in the units of F/(L*L)), 1012 miles long. This is a very magic manometer as it is cut along it's entire length, but once in place instantly seals itself.

    You place the magic manometer into the ocean depths, such that the distance between the two ends is ~ 1000 miles (but you also have a 12,012 mile long magic manometer in case you have ANY doubts). Once in place the magic manometer instantly captures the exact water column throughout.

    Again the same question, why are the two fluid surfaces NOT at the same elevation?

    Both questions have the same one word answer, and it begins with a 'd' and ends with an 'ensity'. D'oh!

    The very 1st thing you learn in any undergraduate hydraulics course is something called hydroSTATICS (as in equilibrium as in STATIC and NOT moving)

    Bonus trick question. If the elevations of the water columns at the two ends of the magic manometer seek a different elevation then the surrounding ocean water levels outside the magic manometer, what physical process occurs within the magic manometer (big hint: something moves, and it isn't the magic manometer, and this word begins with 'hydro' and ends with 'dynamics').

    Now you are still quite unprepared to attempt to read the JFM.

    You might also want to look up geoid and isopycnal.

    You also might want to go to a university and take a dozen+ courses in fluids, then get a job for 30+ years in that field of expertise (field, laboratory and numerical).

    Teh stupit, it burns!

    ReplyDelete
  13. Somebody needs to get Graeme M a GFD tank with an optical altimetry camera!

    http://www.ocean.washington.edu/research/gfd/#aiv

    ReplyDelete
  14. Graeme,

    A fluid is NEVER level in the true sense of being perfectly flat.

    When you take a surveying level and look through it, if forms a perfectly flat 2D surface.

    Look at the Sun or Jupiter or the Moon. Do you consider any of those to be flat, as in a perfectly flat 2D surface.

    In all your examples your horizontal length scale is many orders of magnitude smaller than the radius of the body in question (i. e. the Earth).

    Given a surveying level and a body of water with a horizontal dimension of ~100m and you will just begin to capture the Earth's curvature in that body of water (~0.8mm).

    If you don't believe that then please go here:

    www.tfes.org

    ReplyDelete
    Replies
    1. Everett, are you being deliberately provocative? You second last para seems to imply that you think I am saying water doesn't follow the curvature of the earth. But that is exactly what I AM saying!

      Delete
    2. But the water does not EXACTLY follow the curvature of the Earth. Changes in the density profile lead to changes in the water elevation at different locations caused by different temperature and salinity profiles, differences in the gravity field and the variable bathymetry of the ocean basins.

      Delete
    3. Yes you are right, but we aren't dealing here with the actual water surface. We are dealing with Mean Sea Level, a computed average. Over time, that averaged level is largely coincident with the geoidal surface, to I believe a precision of within 1-2 metres. We could for example substitute, broadly speaking, the geoid (in this case the geoid in question is the one which most closely matches MSL) for MSL. And that pretty much DOES exactly follow the curvature of the earth including local topographic features. I say this not to teach you because you know this better than me, but rather to demonstrate that I *think* I understand generally what is meant by water following the curvature of the earth.

      Delete
  15. As I understand it, Graeme is wanting to argue that the ocean surface is flat and that sea level is going to rise and fall by the same amount everywhere.

    Even assuming he adds the proviso "given enough time", his analogies suggest he is making two big assumptions, both of which would be wrong.

    He assumes that gravity is the only force acting on the water, which is wrong.

    He assumes that the force of gravity is everywhere directed to the centre of the earth, which is also wrong.

    Graeme wouldn't be the first person to think like this, and if a poll were taken, he might find himself with the majority in his thinking. An article about Jerry X. Mitrovica work starts off with:

    "IN THE POPULAR imagination, sea levels rise in response to a warming climate in the same way water rises in a bathtub when the tap is turned on: evenly and uniformly around the globe.

    Until nine years ago, many scientists also assumed the same thing. That’s when professor of geophysics Jerry X. Mitrovica (then at the University of Toronto) and collaborators including Harvard College Observatory associate James L. Davis reported in Nature that incorporating glaciers’ gravitational pull into the equations used to describe sea-level changes would help explain the extreme variation scientists were already seeing around the world..."


    http://harvardmagazine.com/2010/05/gravity-of-glacial-melt

    That doesn't address all the other forces acting on the ocean, mind you - only the force of gravity. It goes on to explain how the mass of ice has its own gravitational pull:

    "In fact, some places on Earth could find the local sea level falling. This is because the sheer mass of glaciers generates gravitational pull and draws water closer, raising the sea level nearby. As glaciers melt, though, this pull weakens and the adjacent sea level falls. At locations far from a given glacier, the most noticeable effect of its melting will indeed be the increased volume that meltwater has added to the sea; closer in, though, decreased gravitational pull becomes the predominant effect."

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    Replies
    1. "He assumes that the force of gravity is everywhere directed to the centre of the earth..."

      To be fair and head off potential confusion, I don't think he does.

      In earlier discussions he made it clear that "level" in this context means "perpendicular to the local gravitational vector", which is essentially the same as saying that "level" here means coincident with the surface of the true geoid.

      However, within that framework he is actually arguing [my clarifications] "that the ocean surface is flat [coincident with the geoid to within a couple of metres] and that [because it's within a couple of metres of the geoid] sea level is going to rise and fall by the same amount everywhere [to within 100mm of so]".

      The head in the sand is evident from the comparison of "couple of metres" and "100mm or so" in that clarified restatement. And also from pointing out that his argument reaches two different conclusions if two different data points are used.

      Delete
  16. I've been rather enamored with this blog site, its objective and its success in pointing out the absurdities posted at WUWT. However, this discourse on sea level has left me aghast since it reads very much like a sophisticated version of WUWT. Graeme asks legitimate questions, naive, but ones which have been asked centuries before by minds clearly greater than any who comment here. It is clear that no one here really understands Graeme’s questions or his perspective, an understanding which must take into account his degree of ignorance (lack of background, not innate intelligence). Since no one really knows what that degree is,one can only surmise and even then in the context of one's individual bias, bias which shines through quite clearly. One needs to interpret Graeme's questions in that context, not your personal context. What I have read in this discussion reminds me of the detailed gobbledegook I've seen countless times when a student attempts to explain a complex problem without really understanding the basics and complexity him/herself. Some who comment have resorted to heckling, which does nothing to help either Graeme, this blog, nor the larger effort to help change misunderstandings about a complex system. Heckling and derision is counterproductive and should be left to WUWT. Helping Graeme sort through the detailed complexities and counterintuitive aspects of this dynamic planetary system means going back to the basics, static systems, and then working stepwise into the increasing complexity of dynamic systems.
    I'll suspect none who comment here ever contemplated the effects on the local gravitational field of the Greenland or Antarctic landed ice masses and the subsequent counter intuitive effects on sea level as the landed ice melts until it was pointed out to you. Surveyors didn’t recognize this significance of this effect on land until the mid-1800s -- if you had intuitively known this, you would have published about the ice sheet melting and sea level long before anyone else. Likewise, I suspect none of those who comment here has ever brought students from a state of no understanding to full understanding of complex systems, a process which can take years. Otherwise your tutorial approach would be very different.
    Remember, all that you think you know so far you have accumulated over the years through a steady progression of education. All the counterintuitive phenomena you now understand you have learned because someone took the time to teach you or you took the time to learn it over the years. So give Graeme a break. Go back to basics as they were understood in 1700 in your explanations/teaching, then work your way forward with each new level of understanding of how hydrostatics expands into hydrodynamics and then, one by one, how the myriad of other static and dynamic forces on the planetary scale conspire to produce the counter intuitive effects which cause so much confusion about the details. Peel the onion layer by layer. Clearly, this approach is beyond the scope of this blog, but what has been provided here has done nothing to elucidate, educate or encourage anyone. And, has left me with an intellectually sour taste.

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    Replies
    1. Jonathon, I do agree. I think this thread has overwhelmed the purpose of this blog and is largely useless to most of the visitors. I think I'd rather take it offline, and engage with one or two people that can work through it with me. I understand that Lotharsson is a smart guy, but he seems intent on muddying simple concepts.

      Sou, I think it's better if we stop here, to protect the integrity of your blog.

      Jonathon, would you be willing to undertake a discussion via email on this one? I'd be just as happy to talk to Lotharsson, but my feeling is that we just aren't going to be able to work this one through. I don't know why he has made this so hard but it sure isn't going anywhere fast.

      Delete
    2. Jonathan,

      It might help to consider the fact that Graeme M previously commented here as "Billy Bob" and apparently also as "Bolt for PM". This isn't behavior that would make other people seriously believe he is actually interesting in learning anything. That is, we have someone who previously showed troll-like behavior, who now supposedly is seriously interested in learning something.

      Delete
    3. It's perplexing to know what GM is arguing (hopefully that doesn't apply to this GM). Originally, it appeared that GM thought that the ocean is flat because water seeks its own level, hence the reference to a tumbler of water. It appears that some of that argument has been deconstructed and reconstructed as averaged MSL matching the geoid and following the shape of the earth. But, maybe that's a misinterpretation of mine, as that 'shape' can't be ellipsoidal as the geoid is 'lumpy' and hence the ocean isn't 'flat'. Furthermore, the literature doesn't say that the averaged MSL matches the geoid. It may approximate it to within plus or minus 1 or 2 metres but that's not uniform across the earth and is not matching it. On reflection, the following comment might have made a better reply than earlier comments for GM.

      Why does water 'seek its own level'? Under the influence of gravity, water flows downhill from a place of higher gravitational potential to lower gravitational potential. Landslides, skydivers, etc. do the same thing. So there's the mechanism, a movement to a lower gravitational potential. Eventually the water stops moving when it reaches the level of lowest potential. So water in a glass, bucket, dam, lake or ocean settles until its surface is at the lowest potential. (Ignoring wind, tidal, standing wave, etc effects)

      Now for the paradox of why the global sea level isn't 'flat'. Or why the ocean's surface doesn't flow from a higher level in the ocean to a lower level (ignoring the effects of winds and tides) and why there are variations in levels of the earth's oceans relative to the idealized ellipsoid of the earth. When the atmosphere and ocean are in equilibrium on a rotating earth, the ocean's surface would have a shape that is called the geoid (ref: Geophysics Dept, Oklahoma University) and here (AW's old uni). The geoid is an equipotential surface which means that the water in the oceans have reached their lowest gravitational potential i.e. they have 'found their own level'. In other words, ignoring the effect of winds and tides, even if the surface of the ocean is higher in one location than another, there is no net movement of the ocean along the geoid from where it is 'higher' to where it is 'lower'. Why? Gravity is everywhere equal along the geoid so there's no imbalance or net force to 'pull' that water into the 'hollows'. Or, all points on the geoid are at the same gravitational potential or 'level' (in a gravitational sense) so there is no ocean water 'seeking its own level'; the ocean water is already there at its own level and, at the same time, the sea level isn't flat.

      And now, JG, put your skills to good use and establish your credentials. Explain to GM (not me, the other one) exactly why SLR is not uniform around the world and get him to actually accept your explanation. Also, OT, could you clarify for GM (me this time), why the earth doesn't lose the moon when the sun's gravity is pulling on it more than twice as much as the earth's gravity? Ta.

      Delete
    4. Jonathan Gradie

      So give Graeme a break.

      No. He isn't listening and worse, he isn't *thinking*. I'm sorry you find the discussion intellectually distasteful, but you are not alone, albeit for rather different reasons.

      Delete
    5. And Jonathan, let us not forget that behind all this crap is an entity called Graeme M / Billy Bob / Bolt for PM who is trying to insinuate that sea level rise is not happening / not caused by thermal expansion of water resulting from an accumulation of energy in the oceans. He says he isn't doing this, but he is. This is climate change denial rather successfully obscured by a vast, tedious and irrelevant excursion into fluid dynamics which, we will recall, started off with half-baked nonsense about seismology. It is easy to lose sight of the fundamental motivations of the climate troll after the first couple of thousand words but one must not. As Lotharsson pointed out on the previous thread, we are watching a hobby horse that has been well exercised elsewhere in the past being ridden round and round and round on this blog. Now that leaves a sour taint on the intellect, or at least it should.

      Delete
    6. I appreciate that this isn't HotWhopper's typical fare, though I think this article and the comments have some useful info and it's not a total loss. For one thing, I've learnt a bit more (as I usually do with every article and comment.)

      I'll also echo BBD's comments. I've given Graeme M/Billy Bob much more than one break over the past few weeks. I was about to ban him for multiple infringements. (Graeme M/Billy Bob features prominently in the HotWhoppery.) He claimed he wanted to understand sea level, so I relented (temporarily) and gave him his own thread.

      Since he's now said he's had enough, that will be the end of it. He won't be commenting here any more.

      Delete
    7. Ah, I see Sou has brought this to an end.

      Jonathon, you might want to understand the background first. Read the previous thread (linked in the OP) and follow the links I posted there back to the thread at Deltoid. I reckon it's not quite the situation you portray it to be.

      I also think given that history I do understand Graeme's questions. An inability to get him to understand my points in response to those questions doesn't imply lack of understanding of the questions themselves.

      And it's not just ignorance of science driving it, there's also a refusal to accept basic logic which is another form of denial which is one of the subjects of this blog. It does not take years to bring a student to understand that if the same argument applied to two different but equally valid data points produces two incompatible results, that either the data or the argument is invalid.

      I got the impression that this time around Bolt for PM/Billy Bob/Graeme M was either attempting to learn something (if only why his arguments don't convince other people) or saying that he was, and took the opportunity to take him at his word. Sometimes that results in intellectual distaste for other people, but no-one is forcing them to read the results.

      Delete
    8. "I'll suspect none who comment here ever contemplated the effects on the local gravitational field of the Greenland or Antarctic landed ice masses and the subsequent counter intuitive effects on sea level as the landed ice melts until it was pointed out to you."

      Why would you suspect that? You may be expressing dismay at this thread but I do not see why you need to make such a sweeping and wrong dismissive statement. I suspect most of the people here have some inkling of the effects.


      Delete
    9. Yes, I thought that was an odd comment to make, particularly seeing that more than one person did the pointing out, which nullifies the "none who comment". Regular readers would be familiar with the work of Jerry Mitrovica. He has been featured here at HW a few times already, for example:

      http://blog.hotwhopper.com/2013/11/sea-level-for-dummies-video-by.html

      http://blog.hotwhopper.com/2013/11/wuwt-readers-are-too-scared-to-read.html

      http://blog.hotwhopper.com/2014/05/the-desire-to-not-look-stupid-is-pretty.html

      Delete
    10. OK so I watched the ~30 minute long Mitrovica video.

      Very informative, and certainly not intuitive at all.

      If I understand what all he is saying, is that the geoid is dynamic (a function of time).

      It sure would be nice to see a time lapse of the changing shape of the geoid though.

      So Graeme M is left with developing a different system of geophysical partial differential equations, showing that "water is level" and publish that in the (E&E) "peer reviewed" literature.

      Dynamic equilibrium. What a concept.

      Delete
    11. Re the gravity issue, I think I misunderstood Jonathan's comment as applying to us all this week. It's more likely he meant commenters here wouldn't have thought of it all by themselves, as he said "until it was pointed out to you" - whenever in the past it was pointed out to us (by Jerry Mitrovica and colleagues or someone else). Which would certainly be true in my case.

      Delete
    12. The other thing that strikes me on reflection about Jonathan's comment is that it seems to be predicated on the only way forward being to teach Graeme to (fairly) fully understand the complex system we're talking about. That presumes the goal of most of the other commenters - and Graeme - is understanding the system, or drawing conclusions that require that understanding.

      I doubt that very much, although in Graeme's case I've operated on this thread with the assumption that he does want to improve his understanding.

      I think it's a reasonable inference from this thread, the previous thread here and the original thread at Deltoid that Graeme's goal is to find a way to conclude that sea level rise due to global warming is not happening and nothing to worry about.

      My own goal is to have readers (and maybe even but not necessarily Graeme) understand the invalidity of his argument asserting that (essentially) one sea level time series observation at one coastal location that (allegedly) doesn't show much change in several decades does not imply that the sea level changes have been the same at all other coastal locations (give or take 100mm) - which implies that any observed variations exceeding this level in sea level rise at different locations around the world are "not real" and hence sea level rise due to global warming isn't anything to worry about. This goal does not require a solid understanding of the complex system as it can be achieved by applying basic logic sans any real climate system understanding to the argument. (Readers will note that Graeme refused to touch that point with a bargepole.)

      It can also be achieved by understanding that the argument relies on ignoring factors that matter as known by people who do understand the complexities of the system (in other words, that the argument springs from too far into the confident incompetent state described by Dunning & Kruger), although I find it's rare that people exhibiting the characteristics of denial rather than mere ignorance who start out there will admit to themselves that that's where they were - perhaps because I don't follow the incremental approach Jonathan recommends?

      All that said, if Jonathan cares to show us how it's done I'd love to see how he would approach it with Graeme and how the resulting dialogue would evolve. We all might learn something really valuable.

      Delete
    13. Lotharsson, you're spot on - ie in line with the reasoning behind HW in general and this thread in particular. It doesn't rely on any assumptions about Graeme or his motivation or any expectations of what he might learn. It was not primarily intended to "teach" Graeme about anything. It's completely unrealistic to expect that a blog can replace years of learning in a classroom environment, or that a single blog article could present all that is known about oceans and sea level.

      The purpose, as with most of HW, is to expose denialist memes and point people to where they can find out more about the science itself. To that end, the article and the comments here aren't too bad, I'd have thought. Not a patch on what we'd learn from a series of lectures by people from the Potsdam institute or Jerry X. Mitrovica. (Graeme would have to pass some pre-requisites in ocean studies before attending, I'd expect, if he wanted to learn from those :D)

      Delete
    14. The main problem as I see it was that BB was trying to apply his simple model, (water in a glass is flat, therefore the ocean is flat, therefore sea level rise can be measured from a single location) while totally ignoring/denying the observations that invalidated his model. This is anti-science, and is typical of denier mentality. Instead of accepting that their model is wrong, deniers will try and gish gallop their way to 'proving' that their model is indeed correct. This is not the first time we have seen this, and I doubt it will be the last.

      Delete
    15. I said I shan't comment here again about any post, and that is the case. I will continue to visit and read. But I had to make one last response to some of the more recent observations, and DJ's above sort of encapsulates what I mean.

      DJ, you are completely misunderstanding my position. Your summary of my simple model is simply NOT what I said. I have no idea why I cannot communicate what seems a relatively simple concept. What you have said is simply nonsensical and if I had such a simplistic naive idea, I'd agree that my arguments are quite fallacious.

      George M above makes an observation about my argument and how that relates to MSL and the geoid, and similarly completely misinterprets my argument.

      Everett then notes that the geoid may be dynamic over time and that this clearly escaped my notice. No Everett, that the geoid varies over time is a completely obvious concept. I do understand that. Not only does it vary over time, but our computation of its surface has improved considerably over time. For example, EGM2008 is a much better model than EGM96. This is thanks to advances in satellite altimetry, notably GRACE measurements.

      Delete
    16. Looks as if Graeme / Billy Bob is trying to make out he's not as ignorant about climate science as his comments over the past few weeks indicate. If that's the case (and I'm not convinced), then his history of (a) dumb denierisms (and (b) tone trolling) over the past few weeks is even more reason to ban him. It would mean he had simply spent the last few weeks trolling for attention, and didn't mean what he wrote. Like I say, I'm not convinced that (a) wasn't for real, though (b) is evident. Whatever. That's it now.

      Delete
    17. "as he said "until it was pointed out to you" - whenever in the past it was pointed out to us "

      OK, I probably misunderstood this. Though that probably applies to 99.9% of what we know. (For the most creative amongst us that is).

      Delete
  17. Well I actually find this a somewhat amusing thread, observing the lack of communication between people who seem to think they are trying. Expertise in fluids is something I know I lack very acutely because just this past week I was working with an expert on a new taxonomy of fluid dynamics and found a series of terms I'd never heard of before - "imbibition" for one. Every subject is more complicated than a first, second, or even 100th experience would suggest to you, and one needs to learn humility in the face of reality. In this respect maybe we would all do well to think about Asimov's old essay on the relativity of wrongness: http://chem.tufts.edu/answersinscience/relativityofwrong.htm
    - Graeme's simplistic view here is wrong, but so is every other explanation offered. Which one is less wrong is a matter of comparison with observation. Can we focus the discussion on the graph posted in the body if the article? Does Graeme dispute the observed changes?

    ReplyDelete
    Replies
    1. "Which one is less wrong is a matter of comparison with observation"

      Indeed. I did try to make pretty much that point earlier...

      Delete
  18. Sou, I do appreciate what you did here, and speaking quite genuinely I can't for the life of me figure out what went on. But I'd definitely like to talk to anyone who's willing to have a serious talk with me so I can see how this went so far astray. I speak seriously when I say I understood every word everyone else wrote, so it beats me why they can't understand me. It's incredibly perplexing. My wife, an ex-science teacher, just shakes her head when she reads this thread. Could I just post my email address here, and leave it at that - I shan't post here again. I'd REALLY appreciate someone getting in touch though.

    gmc99 at bigpond.com

    ReplyDelete
    Replies
    1. Jonathon Gradie, the (private) floor is yours ;-) Let us know how you get on!

      Delete
    2. "I speak seriously when I say I understood every word everyone else wrote"

      No. You really didn't. And that's the underlying problem. You demonstrated repeatedly that you did not understand most of what was explained to you. And no amount of further explanation will help.

      The only way you'll make progress is to go study physics, starting from a very basic level and working up. By the time you get to the point where you have enough knowledge and understanding to think about questions like this people's comments will make sense to you.

      If you do devote the time and effort to that, I wish you luck. If you don't, then please have the honesty to admit (to yourself and others) that *you* don't understand, rather than claiming that it is the scientists who don't "get it."

      Delete
    3. Quite an interesting bit of conversation in which I do not have time at the moment to participate, unfortunately. I think the comment, "The only way you'll make progress is to go study physics, starting from a very basic level and working up," is accurate. Advocating, "If you do devote the time and effort to that, I wish you luck, " is an appropriate "bon voyage;" we all wish Graeme well. Unfortunately, there is truth in, "If you don't, then please have the honesty to admit (to yourself and others) that *you* don't understand, rather than claiming that it is the scientists who don't "get it." This outcome is not something any teacher wishes to see, but we have all witnessed. i am sorry to leave Graeme dangling but I must.

      Delete
  19. I can say one definite thing about "Graeme M" misunderstanding something very basic, having just read the first ~third of the previous post.

    MSL is NOT the same everywhere regardless of what one reads on Wikipedia (or elsewhere on the Internet).

    MSL, historically speaking, was always a LOCAL convention. MSL was never meant to be a universal absolute benchmark, it was, and has been a locally derived relative benchmark, just like MLW, MLLW, MWL, MHW, MHHW are meant to be locality only benchmarks.

    There then are other local "absolute" datums like NGVD29 and NAVD88.

    Finally, there are attempts to define the global geoid in an absolute reference system (global x,y and z).

    I use to be a coastal engineer working for the USACE ERDC WES CHL.

    In that career I did a lot of work on harbor resonance and moored ship motion (nodes and antinodes) for the POLA/POLB (post 1982-3 El Nino (but I did a lot of work on those wave/surge datasets) and afterwards).

    I also did DGPS surveys at Barbers Point HI, Charleston SC and the Panama Canal (during the 1997 El Nino).

    In Charleston Harbor (and the other two) we placed 3 GPS receivers aboard inbound/outbound cargo ships. We traveled ~ 10 miles out to sea and ~20 miles inland (Charleston). In doing that research effort, I came to realize that all the water level benchmarks were local and had NEVER been tied together by ANY surveying method whatsoever. All water level benchmarks were locally defined. Purpose of all these efforts? Define relative and absolute ship motions (like roll and squat).

    So in short:

    MSL = Local relative defined benchmarks
    Vertical Datums = Continental scale absolute defined benchmarks
    Geoid = Global absolute defined benchmarks
    Nodes/Antinodes = locations on minimum changes/locations of maximum changes

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    1. "MSL is NOT the same 'height' everywhere …" (in the potential energy sense). Exactly, EFS. Some parts of the ocean are persistently higher than others due to local factors including temperature and currents. Therefore, tidal datums are superior at measuring relative to the (local) coastline and local sea level, and geoid-based vertical datums are superior at measuring heights consistently over large areas including both ocean and land.

      In a set of papers in the July issue 2009 of Nature Geoscience (behind a pay wall) devoted to sea-level rise, … researchers are acknowledging that a single value of projected sea level doesn't fit all. Satellite data … show that the sea is already rising more quickly in some regions than in others. "Indeed, one of the few statements that can be made with certainty is that future sea-level change will not be the same everywhere."

      Global mean sea level (MSL) isn't a physical constant so much as a concept. For one thing, cold, salty waters occupy less volume than warmer, fresher seas, so MSL tends to be higher near the equator and lower toward the poles. However, trends in temperature and salinity, 'steric' processes, aren't unfolding equally across the globe, because some areas (of seawater) are warming and/or freshening more than others.

      Just as a jet stream in the atmosphere separates zones of higher and lower air pressure, the fast-moving Gulf Stream separates areas of differing MSL as it runs up the Atlantic coast. The average MSL to the east of the Gulf Stream is considerably higher than it is between the current and the shoreline. For example, sea level typically runs about 60 cm (2 ft) higher in Bermuda than in New York. "I don't think most people appreciate this fact," says Michael Schlesinger, a professor at the University of Illinois at Urbana-Champaign (UIUC) who has studied sea-level rise since the 1980s. If the Gulf Stream were to weaken, the difference in sea level on its east and west sides would slacken, thus bringing higher sea levels to the U.S. and Canadian coasts." Source

      Excuse the lazy comment. I lack the pedagogical skills of a JG to take it from the static to the dynamic.

      Delete
  20. I'm the "Mostlyharmless" whose WUWT comment was quoted in the Ocean Chemistry post. I'm a sceptic in the scientific sense (as everyone should be), and see myself as truthful, objective, and hopefully incisive. I delight in exploding myths. I also post under my real name Tony Price.

    I read WUWT because occasionally there's something useful and informative there. I rarely comment there these days - incisive and critical comments are often (usually?) ignored. However, when I see a piece of gratuitous ordure like the Japanese lake research extrapolated to ocean chemistry post, I couldn't remain silent. Introduction over, back on topic.

    The ocean surface is not level, but "lumpy" for various reasons; local gravity, density (temperature, salinity), air pressure, currents, wind, outflow from rivers, rotation of the Earth, tides, changes in Moon's orbit, ocean cycles such as the Pacific Oscillation, North Atlantic Oscillation, and a few others I can't remember just now. MSL change is far from uniform, mainly because of changes in the factors I've listed. I've been studying sea-level change in some depth (pun intended) for several years, and I've come to some (inevitable) conclusions.

    The most significant (as far as this blog is concerned) is that those who claim that global MSL isn't increasing have their heads in the sand; they'll get their hair wet anytime soon. Those who claim that satellite sea-level data is "rubbish" are wilfully ignorant and disingenuous. Steven Goddard and Nils-Axel Mörner are foremost amongst those. The former hasn't ever directly compared satellite data with tide-gauge records over the exact same period, and the latter just lies about it, and sea-level change in general. The mere fact that his off-the-mark, ignorant, and worse-than-misleading outpourings are received uncritically by many (including Anthony Watts) tells you more about them than about him.

    I have to depart (literally) now, but will return soon to comment further on past and present sea-level change. I use the word change deliberately - note the blue and white areas on the satellite graphic above - mainly the central Pacific, and the whole Pacific seaboard of the Americas.

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    1. Welcome to HotWhopper, MostlyHarmless.

      (Here's the link to the ocean chemistry article MostlyHarmless referred to.)

      Delete
    2. I should have included that - my bad.

      I'm working on the correlation between ocean oscillations and sea-level change once more (took a long break from blogging). It's ENSO (Southern Oscillation) which has caused the big difference in sea-level change between east and west Pacific over the satellite period. SOI went strongly negative after 1978, and at many W Pacific sites sea-level actually dropped; at others the rate of rise dropped significantly or to zero.

      After 1994 SOI trended strongly positive, and W Pacific sea-levels reflected that with a strong rebound, which unfortunately pretty-much coincided with the start of satellite altimetry. This has resulted in a distorted view of sea-level rise in the W Pacific. The simultaneous, also correlated, stasis or drop in the central and E Pacific has been largely ignored (white & blue areas on the NOAA graphic above). NOAA is quite aware of the effects of ocean oscillations on sea-level change; it's just that few if any have ever attempted to quantify those effects.

      If SOI stabilises as mostly positive over the next couple of decades, short-term rates of rise should more accurately reflect the underlying trend. I'm preparing a blog post on the subject, hoping to partly fill a gap in our knowledge of such effects.

      Delete
    3. I look forward to your blog article, MH. I've been reading up a bit on ENSO and related topics (eg Indian Ocean and probable ENSO teleconnections) and saw there is discussion in the literature of the link between sea level in some parts and SOI/ENSO.

      Delete
  21. Take a look at how mm the graph has added since this article was posted.

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    1. 2014.7051 65.864
      2014.7323 58.023
      2014.7594 60.736
      2014.7866 67.344
      2014.8137 68.780
      2014.8409 65.301
      2014.8680 65.015
      2014.8951 59.381
      2014.9223 61.591
      2014.9494 70.723
      2014.9766 70.522
      2015.0037 66.662
      2015.0309 64.804
      2015.0580 62.115
      2015.0852 68.589
      2015.1123 69.745
      2015.1395 75.007

      Delete

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