Sea-level rise

Discussion in 'Environmental Discussion' started by tochatihu, May 22, 2019.

  1. tochatihu

    tochatihu Senior Member

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    Is pegged at 3 mm per year globally. Or 3.6. This is a very small number so it's appropriate to to have not been part of recent discussions here. But I must have gotten a wild hair in an improper place so with reader's great forebearance, I'll share.

    Global coastline length is about 356 thousand kilometers. From CIA fact book and no doubt there are others estimating such things. So, how much land area 'goes under' from 3 millimeters?

    A moment's thought reveals one parameter is missing. How steep are coastal slopes? I've not found that, so I made one up. Seriously. This might be 10% (rise over run) or might be quite different from that. But with that value and a spreadsheet too simple to describe, 10.7 square kilometers of land area are inundated per year.

    Double the slope and halve the area. or whatever slope you choose. Take latest published expert assessment of sea-level rise by 2100 (which I recall is less than a meter) and convert it to land-surface area.

    This is doubtfully anything more than my fascination with counting, but dang, somebody ought to do it. Obviously it fails to address many important matters, like future suitability of coastal structures, seawater intrusion into coastal freshwater aquifers, inland penetration of high-water events, among others.

    But I just had to know - y'know? And for careless thread clicking, now you know as well. I hope we are both satisfied...
     
  2. wjtracy

    wjtracy Senior Member

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    Virginia shoreland sinking about the same rate due to glacial period rebound effect and groundwater depletioin...not sure if any places in the world have landmass is rising.
     
  3. tochatihu

    tochatihu Senior Member

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    Glacial rebound in high North is a very big thing. And yet, a slow thing. Greenland is slowly becoming decompressed and will take many centuries to rebound as Nordics are doing now.

    Ice is slow. Rocks are slower.
     
  4. tochatihu

    tochatihu Senior Member

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    May have been Indonesia in news recently for groundwater-depletion sinking? Most of my attention has been elsewhere. But the largest view is that many factors influence tidal gauges.

    Those elevate 'stick in the mud' to a higher meaning. On biotic side, corals are doing their best to keep Pacific islands above water, but for those gangs also, 3 mm/yr is fast.
     
  5. bisco

    bisco cookie crumbler

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  6. Salamander_King

    Salamander_King Senior Member

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  7. fuzzy1

    fuzzy1 Senior Member

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    To extend some careless thread clicking ...

    This rate amounts to just over 3 and a half square feet of lost land per second.

    I don't have much insight to add to the 'average slope' question. But while the many near-vertical cliffs don't lose much area at all, the almost-flat zones will more than make up for them, that is the nature of this nonlinearity.

    For more carelessness, I see a wikipedia page showing average elevations of U.S. states. (Meaningfulness very unclear, as all states have suspiciously coarse round numbers.) If we carelessly assume that Florida and Louisiana (118,000 square miles) have uniform slopes to produce their average elevations of 100 feet, then they lose 5.8 square miles (15 square km) per year. This alone exceeds that earlier planet-wide guesstimate.

    Then apply this to Bangladesh, where most of the land is under 10 meters ASL. It would be losing 22.1 square km per year.

    Oops. Now with just three little 'states', we are now well past triple that original annual land lost estimate, while still ignoring the vast majority of the planet.

    :eek:
     
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  8. tochatihu

    tochatihu Senior Member

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    Average slope of 10% may not be a good guess. But wonderfulness of counting goes deeper than that. Distribution functions matter and examples like this can teach a lot. A small-seeming area of 1% slope throws average values (or medians etc.) right out the window.

    ==
    Seaside cliffs 'just stand there' in context of such analyses. But they are what gets undermined and fall in. Such loss of land certainly matters if your seaside mansion was built there.
     
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  9. Trollbait

    Trollbait It's a D&D thing

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    I'm guessing the decrease in sea level rise as it spills over more land isn't accounted for.
     
  10. fuzzy1

    fuzzy1 Senior Member

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    With 360,000,000 square kilometers of ocean surface area, I'm figuring that 'decrease' rate is far far far too small to be detectable, let alone meaningful.

    We'd need to be flooding 360 sq km per year in order to see even a 1 ppm /year slowdown. Compared to the doubling of the sea level rise rate over my lifetime ...

    Even flooding the entire planet's land surface area, Waterworld-style, would produce only a 30% slowdown. But there isn't anywhere near enough known water available to do that.
     
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