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Sea level rate of change

Discussion in 'Environmental Discussion' started by bwilson4web, Jun 24, 2012.

  1. tochatihu

    tochatihu Senior Member

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    I understand there are three ways for geology to affect seal level. Post-glacial isostatic rebound, local land subsidence (often from local fluid withdrawal), and water being pulled differently by gravity from ice or rock. This is not a clear explanation of the third, but it is a thing and different from the other two.

    Just one among many studies of isostatic rebound, with nice images:

    www.ngs.noaa.gov/CORS/Articles/2006GL027081.pdf

    Land subsidence would occur at smallest scales. Perhaps there is a general review of that topic? Otherwise it would be many site-by-site studies.

    If there are examples of published climate studies ignoring geological effects on 'net' sea level, we could have a look. Actually we've done similar before but I have to search archives for that.
     
  2. tochatihu

    tochatihu Senior Member

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  3. tochatihu

    tochatihu Senior Member

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    I remember that we discussed a particular study that chose 50 (out of many more) US tidal gauges to look for trends. Did not show up by searching here. Maybe remembering wrong, or maybe someone can post a link?
     
  4. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Subsidence and upwelling are well known phenomena that have lead to 'cherry picking' tide records. So it is important to understand that some coastal flooding, like around Lake Charles, also includes subsidence. Houston has a similar problem.

    Bob Wilson
     
  5. bwilson4web

    bwilson4web BMW i3 and Model 3

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    There was a NASA aerial study of an interference instrument to measure wide area subsidence. To the best of my knowledge no one has proposed that mission. Meanwhile, the Jason series have covered the sea level, world wide but I think we need the land studies too. That way smarter decisions can be made about how to mitigate the problems. Some area will have to go but others might respond to well designed solutions.

    Bob Wilson
     
    #45 bwilson4web, May 26, 2017
    Last edited: May 26, 2017
  6. Trollbait

    Trollbait It's a D&D thing

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    Only a warming denier would claim as such.
     
  7. mojo

    mojo Senior Member

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    Because apparently only deniers have the ability to be honest.
    Take subsidence ,measure sea level rise ,then adjust that figure by dishonestly ADDING to that figure accounting for isostatic rebound(which has nothing to do with rising sea levels either) .
    Pure BS.
     
  8. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Source: CU Sea Level Research Group | University of Colorado
    [​IMG]
    Since 1993, measurements from the TOPEX and Jason series of satellite radar altimeters have allowed estimates of global mean sea level. These measurements are continuously monitored against a network of tide gauges. When seasonal variations are subtracted, they allow estimation of the global mean sea level rate. As new data, models and corrections become available, we continuously revise these estimates (about every two months) to improve their quality.

    An accurate technical description of tide metrics: Tide Gauge Sea Level | CU Sea Level Research Group

    [​IMG]

    . . . Although the global network of tide gauges comprises of a poorly distributed sea level measurement system, it offers the only source of historical, precise, long-term sea level data. Major conclusions from tide gauge data have been that global sea level has risen approximately 10-25 cm during the past century.

    Bob Wilson
     
  9. tochatihu

    tochatihu Senior Member

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    http://www.nature.com/ncomms/2014/140414/ncomms4635/abs/ncomms4635.html

    From 2014, how to detect accelerations in trend, possibly already in BobW collection.

    They used only a few sites with long records and corrected for isostatic rebound. AFAIK all serious studies do so; they are reviewed prior to publication. OTOH one could pick a Norway site for example and not correct for isostatic rebound, and obtain opposite result. Might find an affinity website interested in featuring that.
     
  10. tochatihu

    tochatihu Senior Member

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  11. mojo

    mojo Senior Member

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    Its amazing how a satellite can accurately measure a fraction of a millimeter increase ,in a body of water with 30 meter waves.
    Its beyond amazing ,its unbelievable.
     
  12. fuzzy1

    fuzzy1 Senior Member

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    Averaging over thousands of kilometers of ocean surface, and over long time periods, easily takes care of large transient
    waves.

    Signal processing techniques are indeed amazing. We can detect millivolts of DC shifts or tíny other AC signals superimposed on large AC signals, though not with a single data point. Thousands or millions or billions of data points must be processed and averaged.
     
    #52 fuzzy1, Jun 30, 2017
    Last edited: Jun 30, 2017
  13. RobH

    RobH Senior Member

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    Millimeters, inches... Sea level has been 400 feet lower, and there's about 200 feet worth of ice on Antarctica/Greenland.
     
  14. tochatihu

    tochatihu Senior Member

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    ice cores from both polar regions show rapid +T at end of glacial periods and slower -T descending into glaciations. Using the sea-level equivalents of stored ice stated just above, we can calculate average +SLR during the melting times of 18 mm/year. During glaciation, sea level falls at 3 mm/year.

    When the most recent glaciation was melting fast, +SLR was 17 mm/year according to coral records and similar. So there is concordance between these two separate lines of evidence.

    Now there is much less ice to melt. Have suggested before than such rapid melt rates would not be sustainable throughout loss of the 60 meters (sea-level equivalent) of remaining ice. This does not exclude possibility that a few of those meters could 'come off' quickly. If there are some fragile bits here and there. Any century of more than 1 meter of SLR (10 mm/year) would require substantial rapid changes in how humans use coastal areas.

    For context, sea levels were rising 1 to 2 mm/year until the most recent (warmer) decades. Now. 3 to 3.5 mm/year.

    +++
    Have linked above to some recent publications about SLR. Nature Communications bundled up several others:
    Sea level rise research in Nature Communications
     
  15. tochatihu

    tochatihu Senior Member

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  16. tochatihu

    tochatihu Senior Member

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    iplug and Zythryn like this.
  17. bwilson4web

    bwilson4web BMW i3 and Model 3

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  18. iplug

    iplug Senior Member

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    Nice read. Slow moving and less whimsical inertia of our heat sink. Good to point out to denialists (still unlikely to change their beliefs):

    The large fluctuations in GMST and its sensitivity to natural variability mean that using this measurement to argue that global warming is (or is not) happening requires care. An excellent example is the 1998–2013 period, when energy was redistributed within Earth’s system and the rise of GMST slowed [Yan et al., 2016].

    By contrast, the OHC and sea level increased steadily during this period, providing clear and convincing evidence that global warming continued.
     
  19. tochatihu

    tochatihu Senior Member

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    Ocean and atmosphere are our two interacting fluids dealing with energy imbalance in time and space. Not equal partners; ocean about 270 times more massive. Each has characteristic circulation patterns and 'sloshes'.

    This being one&only Planet, improved knowledge of all such details would be valuable even in a time of stable climates.

    All those Argo 'ocean reporters' seem used for temperature vs. depth. There is much more to be learned about ocean dynamics though, and maybe these will make a large contribution.Y'all heard that Paul Allen (rich guy) is providing Argo funding now?