A bunch of stuff I’ll bet you never knew about sea level

Joe Hanson (via a retweet from Gavin Schmidt)  tips us to an interesting video that gives some insight into the complexity of measuring sea level. A good use of 3 minutes follows. Watch.

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67 Responses to A bunch of stuff I’ll bet you never knew about sea level

  1. Brian Cooper says:

    I have long been confused how anybody could measure such a thing. For the most part we haven’t a clue on what goes on under the waves. I first came to this confusion during the 2009 Samoa earthquake. I remember hearing that a huge swath of real estate went vertical x amount of feet. Doesn’t this sort of displacement effect the rise in sea level. of course it does. Does someone compensate for these types of tectonic movements. Haven’t a clue. I doubt I’m the first to think of it.

  2. Robert A. Taylor says:

    Interesting. In the 1950’s I was taught tilt gravimeters reported, by actual measurements, lesser gravity toward mountains and greater toward oceans, because the continental rock was less dense than the sub ocean and the mountain was floating above more dense material with a keel extending into it.

    Does anyone know which is correct?

  3. Ken Hall says:

    Then add in a bunch of inaccurate tidal gauges, add in pseudo scientific alarm, pull down the odd tree on a beach on a Pacific Atoll and before you know it, you too can have an alarmist sea-level scare with which to extort money from Western governments.

  4. Eugene says:

    Wait!

    Did they say in the video that the model correctly estimates sea level to “one meter”????

    How on God’s green earth do we come up with increases or, for that matter, decreases of mm/year?

  5. Sea level? I thought obama had that handled…

  6. EW3 says:

    And they never mentioned the gravitational effect of ofter of other celestial bodies has on sea level. That really can confound things.

  7. philjourdan says:

    You are right! Not so easy to figure it out. But then some can measure it to a single millimeter. (uh huh).

  8. AnonyMoose says:

    “pull down the odd tree on a beach on a Pacific Atoll”

    I think you are referring to the Maldives tree, which is in the Indian Ocean.
    http://www.mitosyfraudes.org/Calen7/MornerEng.html

  9. Bob Greene says:

    Or, you could get your fishing gear and enjoy sea level
    http://www.downeasttour.com/sea_level/sealevel-wecome.htm

  10. spangled drongo says:

    But also if you continually observe at a good benchmark over a 70 year period that king and highest astronomical tides in your tectonically stable neck of the woods actually fall then you can be pretty sure there is not much to worry about.

  11. mikelowe2013 says:

    That reminds me of a stainless steel “marker” I saw last year at the Northern end of Bondi Beach in Sydney. It looked as if it had been damaged in some way, leaning at an angle, and totally unsuitable for giving any indication of sea-level as the minor chop surged up and down. But I’m sure it would produce useful data for the idiots who placed it there, at taxpayers expense, to justify their nonsensical claims for “rising sea levels”.

  12. Steve Keohane says:

    Given how quickly the magnetic poles are shifting, north shifted as much during 2000-2010 as it did 1900-2000, one would guess the gravity fields shift as well. Are they continuously updating their database?
    http://www.ngdc.noaa.gov/geomag/GeomagneticPoles.shtml
    Check out the map at the bottom of the page, a better graphic with more recent (2010) info.

  13. lemiere jacques says:

    I don’t know if i am the only one but to decide to measure sea level instead of sea volume makes the things even more messy?
    quite hard to define a reference and an increase in sea level is only proportional to sea volume in first approximation.

  14. Mike Smith says:

    Terrific little video.

    Of course, this is a gross oversimplification in the context of the climate/sea level change debate. That usually centers on the difference between the (complex) sea level and the equally complex position and movement of adjacent land masses.

  15. mbur says:

    Check out the Sea Height image/animation on this very useful website:

    http://www.stormsurf.com/

  16. mbur says:

    PS.- Thanks for all the interesting articles and comments.

  17. Julian Hancock says:

    As a Hydrographer I have always been interested in mean sea level and the rise an fall of the tide. I have always been blown away by statements saying the sea level has risen by 3mm blah, blah. I know in the real world I have never seen measurements that good even using real time kinematic gps to measure the z component, perhaps +/- 5cm.

    Measuring sea level there are so many sources of error.

    Millie-metric accuracy, they must be using some form of computer modelling?

  18. Eric ah says:

    I read somewhere (Daily Telegraph I think) last week that at any one time there are 100,000 ships at sea. With increasing trade and increasing sizes of ships I wonder what effect their displacement of water has had on sea levels. Any mathematicians out there willing to do a “back of the envelope” calculation?

  19. rgbatduke says:

    I agree. Terrific little video. However, no matter how you measure (or try to measure) SLR, it occurs at a rate of somewhere between 1.5 and 3 mm/year into the recorded past. There is no statitistically admissible evidence of acceleration, and at 3 mm/year (the upper bound of what has been observed we’re talking just over an inch per decade. For the record, it has increased only some 7 to 9 inches since 1870.

    Perhaps it will spike on up to the 1-5 METERS of SLR that form the more extreme predictions of Hansen et. al., just as perhaps the climate will suddenly heat up by 0.5C in two years and rejoin the high climate sensitivity models. However, there is little reason to think that it will given the instrumental records of either SLR or global average surface temperature, and the high climate sensitivity models (that naturally call for maximal SLR) are also maximally failing to have predicted the essentially neutral climate of the last 17+ years.

    Given the DIFFICULTY of measuring SLR, there is probably a serious apples to oranges problem underway — SLR as measured from tide gauges in 1870 is not likely to be particular comparable to gravitation-corrected, GPS corrected, satellite measurements of SLR today, any more than sunspot numbers from the 1870s can be compared to sunspot numbers today without substantial correction.

    rgb

  20. Pete Olson says:

    Interesting – Joe is my wife Frederika Haskell’s nephew

  21. Gunga Din says:

    Great little video.
    I did learn things I didn’t know.
    But one thing I did know before I watched the video is that my head is above water.
    (Give or take 860 feet or so.)

  22. Steve Garcia says:

    Since the video brings it up…

    The roundness of the Earth is often said to be ellipsoidal or an oblate spheroid.

    If shrunk to the size of a billiard ball, however, the Earth is within the same roundness tolerance range of a standard billiard ball. This is even allowing for the deepest ocean trenches and the highest mountains.

    Even generic of Wikepedia admits this:

    Local topography deviates from this idealized spheroid, although on a global scale, these deviations are small: Earth has a tolerance of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls.

    WPA Tournament Table & Equipment Specifications (Effective November, 2001)
    16. Balls and Ball Rack
    All balls must be composed of cast phenolic resin plastic and measure 2 ¼ (+.005) inches [5.715 cm (+ .127 mm)] in diameter and weigh 5 ½ to 6 oz [156 to 170 gms]. [from http://www.wpa-pool.com/web/WPA_Tournament_Table_Equipment_Specifications%5D

    In other words, if the Earth were that small, it would roll as truly as a tournament quality cue ball. I base this on the following:

    Billiard ball — .127mm tolerance/57.15mm diameter = 0.00222 = 0.222%

    Earth — 21km nominal tolerance/12,735km (nominal diameter) = 0.00165 = 0.165%

    So, nominally, the Earth is more truly round than a billiard ball.

    Now, if we take into account high and lowest points, which points are they and how high are they?

    [from Wiki>Marianas Trench] The trench is not the part of the seafloor closest to the center of the Earth. This is because the Earth is not a perfect sphere: its radius is about 25 kilometres (16 mi) less at the poles than at the equator.[5] As a result, parts of the Arctic Ocean seabed are at least 13 kilometres (8.1 mi) closer to the Earth’s center than the Challenger Deep seafloor.

    and

    [from Wiki>Extreme points of Earth] The point closest to the Earth’s centre (~6,353 km (3,948 mi)) is probably at the bottom of the Arctic Ocean (greatest depth 5,450 m (17,881 ft)) near the Geographic North Pole (the bottom of the Mariana Trench is near 6,370 km (3,958 mi) from the centre of the Earth).

    So we end up with this:

    Chimborazo at 6384 km height yields a 12,768 km diameter.

    The 6353 km deepest Arctic Ocean height yields a 12,706 km diameter.

    So, for Earth that would be 12,735km nominal diameter +33km / -29km. Let’s use a 31.0 km average of the two.

    That comes to 31.0km / 12,735km = 0.00243 = 0.2434%.

    So, even using the most extreme individual points on Earth, the roundness tolerance for the Earth is BARELY outside the standard tolerance for tournament billiard balls – 0.24% vs 0.22%. And I guarantee that many perfectly tested billiard balls have single microscopic POINTS outside that 0.22% range – especially on the negative side, which would not be easily measured; probe tips would not be small enough. (The Marianas Trench, for example, would not show up with standard measuring equipment.)

    And, again, using the nominal polar and equatorial diameters of Earth, then the Earth is well within the tolerance range for billiard balls – 0.16% vs 0.22%.

    So, the idea of the Earth being oblate is technically true, but in a real-world sense it is really still round.

    Either that or we need to start calling pool balls oblate spheroids.

  23. DCA says:

    I don’t know how the SL is measured but as a surveyor we use the latest GPS equipment and the verticle accuracy is only 1 cm at best.

  24. Psalmon says:

    The more you learn about sea level, this and Dr. Soon’s video presentation, the more you realize the sea is rising as much as the sky is falling.

  25. Latitude says:

    one would think…..if the Mississippi river can deposit enough silt to make New Orleans….
    but then, I’m sure all of the sea level rise is because of CO2….and higher temps hiding in the deep ocean

  26. Steve Reddish says:

    Steve Garcia says:
    November 26, 2013 at 2:18 pm

    “If shrunk to the size of a billiard ball, however, the Earth is within the same roundness tolerance range of a standard billiard ball.”

    But the Earth is not the size of a billiard ball! The Marianas Trench does show up with our standard measuring equipment. If the Earth was shrunk to the size of a billiard ball, and we were shrunk with it, our measuring equipment would still be able to detect the Marianas Trench.

    So, the point of your post escapes me??

    SR

  27. Duster says:

    lemiere jacques says:
    November 26, 2013 at 12:44 pm

    I don’t know if i am the only one but to decide to measure sea level instead of sea volume makes the things even more messy?
    quite hard to define a reference and an increase in sea level is only proportional to sea volume in first approximation.

    Sea level is at least relatively measureable. Ocean volume is far less exactly known. We don’t have anywhere near the necessary mapping precision of marine basin topography yet for one thing. Besides, even with that quality mapping, in order to estimate the volume, you would still need an estimate of sea level. Ocean basins are not graduated like measuring cups.

  28. Pippen Kool says:

    Eric ah “With increasing trade and increasing sizes of ships I wonder what effect their displacement of water has had on sea levels.”

    2.15 billion cubic meters divided by the surface area of the oceans equals about 6 microns (0.006 mm).

    http://what-if.xkcd.com/33/

    But the article goes on: you don’t have to worry about that six-micron sea level drop. The oceans are currently rising at about 3.3 millimeters per year due to global warming (through both glacial melting and thermal expansion of seawater).

  29. Alan Mackintosh says:

    Re steve Garcia,
    Is the emphasis of the spheroid not increased as the sea, being a fluid, will tend to be thrust out due to centrifugal force near the equator, and presumably drag some fluid from the poles to compensate?

  30. agfosterjr says:

    Robert A. Taylor says:
    November 26, 2013 at 12:09 pm
    ===========================================
    You learned right. See: http://en.wikipedia.org/wiki/Gravity_anomaly
    But that’s low resolution. At high resolution big marine volcanoes do attract the sea and raise sea level a little. –AGF

  31. Jimbo says:

    What I find absolutely astonishing about some Warmists is when they say stuff like:

    “But the sea levels are rising!”

    I then remind them that this has bee happening since the last de-glaciation. Then I tell them that the rate has flattened in the last few thousand years and there is no concrete evidence for acceleration. Sure, they show me references and I show them references to the contrary.

    American Meteorological Society – Volume 26, Issue 13 (July 2013)
    Abstract
    Twentieth-Century Global-Mean Sea Level Rise: Is the Whole Greater than the Sum of the Parts?
    ………..The reconstructions account for the observation that the rate of GMSLR was not much larger during the last 50 years than during the twentieth century as a whole, despite the increasing anthropogenic forcing. Semiempirical methods for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of the authors’ closure of the budget is that such a relationship is weak or absent during the twentieth century.
    http://dx.doi.org/10.1175/JCLI-D-12-00319.1

    Journal of Coastal Research – 2011
    It is essential that investigations continue to address why this worldwide-temperature increase has not produced acceleration of global sea level over the past 100 years, and indeed why global sea level has possibly decelerated for at least the last 80 years.
    http://www.jcronline.org/doi/abs/10.2112/JCOASTRES-D-10-00157.1

    Sea level rise is not an easy one to measure by any measure.

  32. Jimbo says:

    Pippen Kool says:
    November 26, 2013 at 2:49 pm
    …………………
    But the article goes on: you don’t have to worry about that six-micron sea level drop. The oceans are currently rising at about 3.3 millimeters per year due to global warming (through both glacial melting and thermal expansion of seawater).

    Pippen, have you wondered what else might cause sea levels to rise?

    Global groundwater depletion leads to sea level rise
    Large-scale abstraction of groundwater for irrigation of crops leads to a sea level rise of 0.8 mm per year, which is about one fourth of the current rate of sea level rise of 3.3 mm per year.
    http://www.un-igrac.org/publications/422

    Here is the study.

    Abstract – 26 OCT 2010
    Global depletion of groundwater resources
    [1] In regions with frequent water stress and large aquifer systems groundwater is often used as an additional water source. If groundwater abstraction exceeds the natural groundwater recharge for extensive areas and long times, overexploitation or persistent groundwater depletion occurs. Here we provide a global overview of groundwater depletion (here defined as abstraction in excess of recharge) by assessing groundwater recharge with a global hydrological model and subtracting estimates of groundwater abstraction. Restricting our analysis to sub-humid to arid areas we estimate the total global groundwater depletion to have increased from 126 (±32) km3 a−1 in 1960 to 283 (±40) km3 a−1 in 2000. The latter equals 39 (±10)% of the global yearly groundwater abstraction, 2 (±0.6)% of the global yearly groundwater recharge, 0.8 (±0.1)% of the global yearly continental runoff and 0.4 (±0.06)% of the global yearly evaporation, contributing a considerable amount of 0.8 (±0.1) mm a−1 to current sea-level rise.
    http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/abstract

    It’s not as simple as you previously thought!

  33. Jimbo says:

    Will groundwater abstraction get worse if we don’t act now?

    BBC – 20 April 2012
    Scientists say the notoriously dry continent of Africa is sitting on a vast reservoir of groundwater.

    They argue that the total volume of water in aquifers underground is 100 times the amount found on the surface.
    http://www.bbc.co.uk/news/science-environment-17775211

    The abstract of the paper is here.

  34. Steve Reddish says:

    Since tidal gauges all around the Baltic Sea have displayed isostatic rebound of the coastline, is it not safe to assume that entire basin is on the rise, displacing seawater out into the North Atlantic? Likewise, for most of northeastern Canada? These are just two examples of how rising or falling sea bottoms around the world would have a tremendous effect upon global sea level. How could any human caused SLR, if there is such a thing, even be determined?

    Since coastlines likewise rise and fall, all that really matters now that continental ice sheets of North America and Eurasia are melted, is the rise or fall of local sea level. Global sea level rise is swamped by local sea level changes.
    As those areas that are subsiding have been doing so since before industrialization and people have been able to cope with the local rise of the sea, this is an artificial crisis created to bolster that other artificial crisis – CAGW.

    SR

  35. David in Cal says:

    Very nice video. Of course, from the standpoint of CAGW, the key isn’t sea level, but sea level change.

  36. ATheoK says:

    “Brian Cooper says: November 26, 2013 at 12:06 pm

    … I doubt I’m the first to think of it.”

    You just might be!

  37. Mike Rossander says:

    Robert A. Taylor at 12:09 pm above asks about tilt gravimeters showing lesser gravity toward mountains and the apparent contradiction with the video.

    Both are true. The difference is in where you take the measurement. The experiments in the 1950s were made based upon measurements relative to the surface. Those measurements would correctly show that continental rock is less dense (and thus has less gravitic effect).

    The video’s calculations assume an external orbit uniformly above both the mountains and oceans. From that perspective, the less-dense mountain sits in a depression in the denser crust. But the ocean also sits in a depression in the crust. The sum of mountain plus crust is greater than the sum of ocean plus crust, leading to the video’s “puddling” of gravity around mountains.

  38. stuart L says:

    Hmm We want to know if the sea level is rising and how much, so why measure it all over different places, if we took just three measurements in places that were not affected by gravity, isostatic rebound etc, like one in the Atlantic, one in the Pacific and one in the Indian ocean. wouldn’t that be more representative of true sea level rise.

  39. Brent Walker says:

    There is also the tidal effect of extra-terrestrial bodies such as the moon and the sun (and the great planets when they are in alignment.
    What about erosion. When I visited the ancient city of Troy, which was a port a few thousand years ago I found it is now 14 kilometers from the sea. Apparently this is because the river that was next to Troy has dumped so much sediment from the mountains in Turkey into the sea at that point. It makes you wonder how much sea level rise is due to sedimentary increases. This would be accelerating as mankind develops cities and towns. Another source is deliberate dumping of waste into the ocean. The OK Tedi mine in Papua New Guinea comes to mind as 80 million tons of waste was dumped each year into the local river which in turn would have taken most of that to the sea.

  40. Curt says:

    The video, while raising many valid points, is only scratching the surface (sorry if that sounds like a pun) of the problems in trying to measure sea level changes. Prevailing weather patterns of high and low pressure, plus general wind direction and magnitude, can lead to significant changes in sea level at various locations. For instance, California levels are quite a bit higher during El Nino periods.

    Geological effects include isostatic rebound at high latitudes, seismic movement, and human induced pumping of groundwater and/or petroleum.

    Satellite measurements bring in a host of other issues. Fundamentally, they measure distance from the satellite to the sea surface by measuring the speed-of-light delay in bouncing a laser off the surface. But the speed of light varies with atmospheric conditions such as temperature and humidity that are not that precisely known.

    The fundamental resolution of the satellite measurements is far above the annual trend they claim to measure. I believe it is only recently that this base resolution has gone below 1 meter. It is only by averages of averages of averages that can claim the precision to measure the trends.

    Also, the satellite altitude is not that precisely known either. All of the gravitational variations that the video mentions do affect the satellite’s trajectory at this level of precision, as well as density variations in the very tenuous, but still real, atmosphere, there. So the measurements must all be calibrated against ground measurements.

    Many other issues as well…

  41. TNA says:

    Speaking as sailor, I’ve yet to see a change to the lowest or highest astronomical tide measurements on any nautical chart. Nor have I managed to find detail that any have ever changed as a result of climate change.

    http://thenewaustralian.org/?p=10285

    To misquote Joe Strummer; London ain’t drowning and I….. live by the river!

  42. RoHa says:

    There is no problem with finding sea level. Go down to the beach and find the sea. (Look for something big, wet, and moving slightly. No, not that. Bigger, and made of water.) Found it? Now look at the top of the sea. Sea level is where to top of the sea is.

  43. mbur says:

    @Brent Walker “What about erosion. When I visited the ancient city of Troy, which was a port a few thousand years ago I found it is now 14 kilometers from the sea. Apparently this is because the river that was next to Troy has dumped so much sediment from the mountains in Turkey into the sea at that point. It makes you wonder how much sea level rise is due to sedimentary increases. This would be accelerating as mankind develops cities and towns. Another source is deliberate dumping of waste into the ocean.”

    Maybe that’s part of the Anthropogenic part of it.People are always changing (i.e. Port Building, Levees,Dredging,Canal Building) their environment .But,i think that natural forces dominate the system.My comment on another article:http://wattsupwiththat.com/2013/11/26/real-pollution-not-carbon-pollution-increases-storm-clouds/#comment-1484975 ,IMO,says that also.What i mean is that the high pressure(more dense) cold weather(air) system causes an inversion layer where it pushes down on the lower level emissions.Warming is not caused by the anthropogenic forcing because of the natural atmosphere phenomena.Well,that’s what i’m thinking,Who really knows?

    Thanks for the interesting articles and comments.

  44. Sea Level Trends – NOAA Tides & Currents, at http://tidesandcurrents.noaa.gov/sltrends/sltrends.html might be of interest.

    [Very interesting NOAA reference page, Thank you. Mod]

  45. lee says:

    Sea level rise due to subsidence seems incongruous.

  46. Peter Miller says:

    And to top everything, we rely on sea level measurements, using the speed of light, from satellites in decaying ellipsoid orbits.

    Then there are also these factors to consider: wave heights, currents, tides, winds, isostatic rebound, tectonic movements and seasonal changes in ocean temperature.

    And we believe we can measure changes in sea levels to an accuracy of 0.01mm!?!

  47. Bychart says:

    What about erosion. When I visited the ancient city of Troy, which was a port a few thousand years ago I found it is now 14 kilometers from the sea. Apparently this is because the river that was next to Troy has dumped so much sediment from the mountains in Turkey into the sea at that point.

  48. eo says:

    The video missed one important aspect of sea level which is the rotational speed of the earth. The earth moves from west to east. Land mass are fixed to the earth while the sea being liquid is mobile. Long land mass such as the north and south america practically slams the water in the Atlantic Ocean and in the process increases the sea level and in the process creates a slight vacuum on the Pacific Ocean side reducing the sea level. The separation could be very short as in the Panama canal, it could have the same gravitational force, same force of attraction from the land mass within this small area, but the sea level could be different on each side of land mass.

  49. ColdinOz says:

    Psalmon says: “The more you learn about sea level, this and Dr. Soon’s video presentation, the more you realize the sea is rising as much as the sky is falling.”

    And according to the IPCC (and no one else) that is very very fast.

  50. Bertram Felden says:

    I love Minute Physics.

  51. Paul Homewood says:

    Or you can just adjust the measurements to what you would like it to be!

  52. Birdieshooter says:

    Andres Valencia-

    When looking at the map and the difference between the New Orleans area and say Miami or Charleston, we can see how much subsidence influences the numbers. Likewise isostatic rebound up in Alaska. Lots of things going on. That is a great map.

  53. Tom Moran says:

    Bychart says:
    November 26, 2013 at 11:55 pm
    What about erosion.
    I agree, what about all the land that is added to the water? Doesn’t that just push sea level up? Linear in, linear up…

  54. Disputin says:

    You lose.
    I’ve known about orthometric vs. geodetic heights for some time, but then, as a sea surveyor for some 35 years, so I should.
    Some others above have mentioned actual sea level measurement, so here goes.
    I had a chat at a trade show to some chaps from the Proudman Oceanographic Lab (one of the froremost labs in the world for tidal matters) about their charts displaying how sea level is rising due to Global Warming and asked them how they measured it. The answer came that they took them from a network od tide gauges, as I’d expected. Where were they? I queried? Placed like Sydney, Hawaii, Cape Town, Bombay, etc. So, on the forearc of growing mountain ranges, a bloody great shield volcano, etc., etc.?
    In the UK, Land Levelling Datum is at Newlyn, in the southwest. By carefull levelling, this level has been carried accross the country. You use it to put in a tide gauge. When you’re doing surveys for a navigational chart, though, your average seafarer couldn’t give a monkey’s about Newlyn, he wants to know how much water he’s got under his keel. So you usually choose a zero datum such that the sea level will almost never get that low, and call it Chart Datum. Then you work out the relation between that and the land levelling datum, so that you can relate stuff on land to the water. Clear so far?
    OK, how was the Newlyn Datum determined? By years of careful observations of Sea Level! So land levels are determined from sea level, and sea levels from land levels. ???
    In addition to which, only about 18,000 years ago there was a couple of miles of ice sitting in the centre of Great Britain, which pushed it down. As the Earth has about the consistency of jelly at that scale, the land arond the edges bulged up in a Periglacial Bulge. Quite suddenly, the ice melted, so the Pennines are now rising and the periglacial bulge (including Newlyn) is sinking. Or would be if the whole island wasn’t also tilting to the south east.
    That’s the UK, with probably the oldest records and expertise in tidal and sea level measurement. The rest of the world is later, with less well understood data.
    You still want to believe in global sea level rises at all, let alone a few millimetres per century?

  55. Disputin says:

    Apologies for typos. Why can’t we edit this?

  56. Disputin says:

    eo says:
    November 27, 2013 at 12:07 am

    Not so, the rotation is (more or less) constant, so Newton’s First Law of Motion applies.

  57. Alberta Slim says:

    Peter Miller says:
    November 26, 2013 at 11:49 pm
    “And to top everything, we rely on sea level measurements, using the speed of light, from satellites in decaying ellipsoid orbits.

    Then there are also these factors to consider: wave heights, currents, tides, winds, isostatic rebound, tectonic movements and seasonal changes in ocean temperature.

    And we believe we can measure changes in sea levels to an accuracy of 0.01mm!?!……………”

    Yes, I totally agree with Peter.
    And, are tides factored in accurately?

    The UN IPCC sea level scare is a COS in my opinion.

  58. Yes, Birdieshooter, thanks. We can see the details in the arrows and the trend values. http://tidesandcurrents.noaa.gov/sltrends/ is definitely a good map by NOAA’s Tides&Currents.

  59. vuurklip says:

    Off topic, sorry, but have you seen this? Groningen (Netherlands) suffered a level 3 earth quake which is ascribed to gas recovery by the Nederlandse Aardolie Maatschappij. 69 Building have been damaged. See here:
    http://www.nrc.nl/nieuws/2013/07/03/enkele-schademeldingen-na-lichte-aardbeving-in-groningen/

  60. rgbatduke says:

    That’s the UK, with probably the oldest records and expertise in tidal and sea level measurement. The rest of the world is later, with less well understood data.
    You still want to believe in global sea level rises at all, let alone a few millimetres per century?

    I don’t think things are quite as bad as you make them out to be. People have been sailing the world for hundreds of years, and there is reasonably reliable tide gauge data from all over the world going back well over 100 years. The tide gauges, it is true, won’t reflect coastal uplift, but on average one expects uplift and sinking to about balance — some places may rise, but others will fall. Even without any effort made to identify those places/trends by other means, I rather trust the average of tide gauge data (more than I trust satellite data, actually — to many modern apples being compared to historical oranges).

    It isn’t a few millimeters a century, either — it is a few millimeters a year, 2-3 cm/decade, some 20 cm/century. Again, the tide gauges might or might not do a good job of resolving a year’s changes on a scale of mm, but 2 cm is pretty hard to miss and 2 cm plus or minus 2 mm pretty easy to believe. That’s the kind of result summarized here:

    http://en.wikipedia.org/wiki/File:Trends_in_global_average_absolute_sea_level,_1870-2008_%28US_EPA%29.png

    One can worry about whether or not the satellite numbers in the last 15 years of this figure (that doesn’t seem to extend to 2013 for some reason) are comparable, and as has been pointed out in other posts/threads, some of the tide gauges used are probably rejectable on the basis of egregious coastal changes as opposed to actual SLR, but there is little doubt that the tide gauges themselves show a total SLR of around 9 inches over 140 years, and there isn’t any particularly good reason to doubt that the sea level is currently continuing to rise at a rate of around 3 mm/year. That rate is hardly unprecedented in the tide gauge data — there are steeper rises in the 1930-1950 early 20th century warming (that was almost certainly not driven by CO_2) — and it is not, actually, alarming. It is boring. If SL continued to rise at 3 mm/year for the rest of the century nobody would, or should, much care, any more than there has been any panic caused by a rise of about that rate in the last century. Coastal changes due to other factors (such as hurricanes or changes in tidal current patterns or due to silting) are usually a lot more important and happen a lot faster.

    In a sense, whether the isostatic level of “the sea” is rising is irrelevant anyway. What we care about is whether or not it is rising on the coasts, and coastal gauges are a direct measure of this. What satellites show about the ocean bulging (or not) in the middle of the Atlantic is almost irrelevant.

    The major fraction of SLR comes not from land-based ice melt, but from the thermal expansion of the water above the thermocline as it gradually warms post-Wisconsin glaciation. There are lovely and again, fairly reliable pictures of this:

    http://en.wikipedia.org/wiki/File:Post-Glacial_Sea_Level.png

    Note well the scale is twenty METERS — the thickness of the line is around a meter, and the entire changes in the former figure over a century aren’t even close to this. Note also the time scale of things like “the meltwater pulse” produced when the land mass glaciers rapidly melted, to be terminated by the Younger Dryas (return to partial glaciation for a thousand years or so). The slope of SLR on this timescale appears to still be rising as it approaches the present at a rate of a meter per thousand years, but note well that the data does not resolve to annual or even century scale changes — it is pretty sparse. Nevertheless, if you look closely you can see a single red dot corresponding to the MWP and a single dot corresponding to the LIA at the far right hand edge of the curve, suggesting that the current SLR is still dominated by “rebound” from the SLF (sea level FALL) of the LIA, and that the current level is within a hair of the average over several thousand years (where a “hair” on this scale means “within a meter” since smaller variations are invisible).

    This is a very instructive figure, actually. If we return to glaciation, one of the first effects is going to be the leaving of all of the world’s major ports high and dry. Note that the change in SL over 22,000 years was a rise of 120 to 130 METERS, and that, if anything, the rise rate has come very close to levelling. OTOH, even in the worst of the warming rises, SL did indeed rise five to ten meters “overnight” (over a few hundred years). This makes Hansen’s claim of a 5 m SLR over a century “barely” believable, if one assumes that the entire continent of Antarctica and/or the entire Greenland plateau start to melt in a near-tropical breeze. More realistically, the rise rate during the Holocene Optimum, when temperatures were at their highest and there was still a lot of unmelted ice was around a meter/century (a rate that persisted for some 4000 years, BTW). EVEN with temperatures that persisted at or close to optimum levels from 7000 to 9000 years ago, SLR had long since tapered off since most of the temperate zone glaciers were gone and the remaining ones were largely immune to global warming.

    Just one of many things that we don’t really understand and cannot model.

    rgb

  61. NOAA report: The Budget of Recent Global Sea Level Rise 2005-2012

    For decadal and longer time scales, global mean sea level change results from two major processes that alter the total volume of the ocean.
    Changes in the total heat content and salinity produce density (steric) changes.
    The exchange of water between the oceans and other reservoirs (glaciers, ice caps, and ice sheets, and other land water reservoirs) results in mass variations.
    With sufficient observations of sea level, ocean temperatures and salinity, and either land reservoirs or ocean mass, the total budget of global mean sea level can in principle be closed.
    Expressed in terms of globally-averaged height, contributions to the total budget of global mean sea level are

    SLtotal = SLsteric + SLmass

    where SLtotal is total sea level, SLsteric is the steric component of sea level, and SLmass is the ocean mass component.

    In this analysis, the global sea level rise budget for 2005-2012 is closed when the Paulson GIA correction is applied. The sum of steric sea level rise and the ocean mass component has a trend of 1.1 ± 0.8 mm/a over the period when the Paulson GIA mass correction is applied, well overlapping total sea level rise observed by Jason-1 and Jason-2 (1.3 ± 0.9 mm/a) within a 95% confidence interval.

    From The Budget of Recent Global Sea Level Rise 2005-2012 (.pdf, NOAA report, June 2012. Revised January 2013)

    See also NOAA Tides & Currents (Operational Oceanographic Data)
    – Sea Level Trends (World Map), at http://tidesandcurrents.noaa.gov/sltrends/

  62. The The Budget of Recent Global Sea Level Rise 2005-2012 (.pdf, NOAA report, June 2012. Revised January 2013) is at http://ibis.grdl.noaa.gov/SAT/SeaLevelRise/documents/NOAA_NESDIS_Sea_Level_Rise_Budget_Report_2012rev1.pdf

  63. Chris R. says:

    To rgbatduke:

    Have you ever visited the late John Daly’s site,
    “Still waiting for Greenhouse”, particularly the
    area devoted to the sea level measurements at
    the “Isle of the Dead” near Tasmania?

    http://www.john-daly.com/deadisle/index.htm

    Seeing a mark that was struck in 1841 still above
    sea level in 2004 puts the 20-30 cm/per century
    in doubt. John Daly, who was an amateur observer,
    but in my opinion, a careful one, estimated only 2.5
    cm of sea level rise over 160 years at this marker.

  64. Rathnakumar says:

    Interesting video, Mr. Watts!

  65. Robert A. Taylor says:

    @ agfosterjr says:
    November 26, 2013 at 3:09 pm
    Robert A. Taylor says:
    November 26, 2013 at 12:09 pm
    ===========================================
    You learned right. See: http://en.wikipedia.org/wiki/Gravity_anomaly
    But that’s low resolution. At high resolution big marine volcanoes do attract the sea and raise sea level a little. –AGF
    ===========================================

    So 1950’s Geology 101 agrees with Wikipedia.
    Since the Video was wrong about that, I wonder what else it was incorrect about.

  66. hideki motosua says:

    May seem like a stupid question to some but what happens on the sea bed?Is it an impermeable membrane or can water leak through it and if so what happens to it.To use a crude analogy is the basin a bit like a bath tub where you can let water out by pulling the plug?

  67. richardguy72 says:

    The interesting video shows the complexity of measuring sea level. The point, clearly made, is that sea level is a mythical entity. Having realized that we also have to realize that “Isostatic Rebound” is also a mythical entity: it does not exist. Darwin deduced erroneously that the land rose from the sea, what he termed “Raised Beaches” Agassiz built his Post Glacial Rebound Theory on Darwin’s error by stating that ” The reason the land rose from the sea is because of the Great Ice Age burden which depressed the land: now that the Ice has melted the land is rebounding” The original Darwinian observation was fiction and hence the Agassiz theory of Post Glacial Rebound is also fiction.

    It is time that the error is corrected. V. Mueller has stated that if you multiply the Hubble Constant by the Radius of the Earth we get the rate of Isostatic Rebound. What Mueller has shown, mistakenly, is profound proof of Earth Expansion. The rate Mueller has shown is the same rate of the earth’s expansion proposed by Earth Expansionists. So Mueller has shown unwittingly that the earth is expanding at a rate which is identical to the rate of Isostatic Rebound. If Post Glacial Rebound is mythical the rate of expansion must be attributed to the actual expansion of the earth. Richard Guy Mse, Structural Engineer. [number removed, mod]

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