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New York Flood Risk through 2300 CE

  1. Nov 10, 2017 #1
    This recent Open Access article in PNAS reviews flood risks in NY through 2300 CE. The findings are summarised in the Significance paragraph:

    We combine downscaled tropical cyclones, storm-surge models, and probabilistic sea-level rise projections to assess flood hazard associated with changing storm characteristics and sea-level rise in New York City from the preindustrial era to 2300. Compensation between increased storm intensity and offshore shifts in storm tracks causes minimal change in modeled storm-surge heights through 2300. However, projected sea-level rise leads to large increases in future overall flood heights associated with tropical cyclones in New York City. Consequently, flood height return periods that were ∼500 y during the preindustrial era have fallen to ∼25 y at present and are projected to fall to ∼5 y within the next three decades

    I find it an interesting example of the kind of practical study that can inform decisions on how to mitigate the effects of global warming.
     
  2. jcsd
  3. Nov 12, 2017 #2

    mfb

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    New York can build a wall if necessary. The Dutch built a wall, and then some more. London has a wall. Saint Petersburg joined recently.

    Developed countries can manage this and build walls for populated areas with quite a small fraction of the GDP. Other countries will have more problems.
     
  4. Nov 16, 2017 #3
    Here is a further example of research that can inform decisions to mitigate the effect of climate change. A news article on the BBC alerted me to this technique for identifying cities at risk of future flooding due to ice melt and pinpointing the ice masses most likely to impact them. The authors note that:

    As land ice is lost to the oceans, both the Earth’s gravitational and rotational potentials are perturbed, resulting in strong spatial patterns in SLR, termed sea-level fingerprints. We lack robust forecasting models for future ice changes, which diminishes our ability to use these fingerprints to accurately predict local sea-level (LSL) changes. We exploit an advanced mathematical property of adjoint systems and determine the exact gradient of sea-level fingerprints with respect to local variations in the ice thickness of all of the world’s ice drainage systems. By exhaustively mapping these fingerprint gradients, we form a new diagnosis tool, henceforth referred to as gradient fingerprint mapping (GFM), that readily allows for improved assessments of future coastal inundation or emergence.

    from E.Larour et al "Should Coastal Planners have concerns over where land ice is melting?" Science Advances 15 Nov 2017:Vol. 3, no. 11
     
  5. Nov 17, 2017 #4

    Evo

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    One bit of good news is that if the ice is from land, the land will eventually rise as the weight of ice is lifted, reducing the rise of sea levels. The main concern is ice melting that is not on land.
     
  6. Nov 17, 2017 #5

    mfb

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    Rising land only helps where the ice was and only at coasts. Greenland will gain a bit of land, Antarctica will gain some land. Not the most popular places. And the rise of the land is a very slow process. Meanwhile all other coasts have to deal with rising sea levels.

    Melting sea ice doesn’t change the sea level.
     
  7. Nov 17, 2017 #6
    True, but it is rather delayed good news. The rise in sea levels is practically instantaneous, whereas isostatic adjustment to reduced ice load takes years, centuries and millenia. Scandinavia is still rising today, some 10,000 years after the loss of most of its ice and this rise is likely to continue for a further 10,000 years.
    Also, uplift in one area may be accompanied by subsidence in another. For example, in the UK, where the glaciers never extended beyond the current line of the Thames, the north of Britain continues to rebound, but south of this line it is sinking. This will exacerbate the effect of any separate sea level rise.

    (Having written that, I note mfb made the same first point, but more concisely.)

    Sea ice melt will have a minor effect on sea level on account of thermal expansion, but this will be complicated by the fact that maximum density occurs at around 4o Celsius. IIRC we should see an increase in volume on initial melt, a reduction in volume as (and if) the water temperature rises to 4o and thereafter, an increase in volume.
     
  8. Nov 17, 2017 #7

    Evo

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    All very good points. And a good point on the sea ice, for some reason I was thinking of melting water runoff where ice still remained on land, but that just shows why you shouldn't post while you're waiting for a root canal. I made no sense! o:) I will return to reading and taking pain pills.
     
  9. Nov 17, 2017 #8

    phinds

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    Ouch ! Good luck w/ that.
     
  10. Nov 17, 2017 #9

    jim hardy

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    Just when i thought it was safe to go in the water..



     
  11. Nov 20, 2017 #10
    This is another fascinating example of how intuition can lead you in completely the wrong direction. When an Ice Sheet melts sea level drops locally? No way!!
     
  12. Dec 1, 2017 #11

    Tom.G

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    Please be careful about absolutism. A quote from Science magazine:
    "http://www.sciencemag.org/news/2017...s-arrived-boat-now-they-re-beginning-prove-it

    "To maximize their chances of finding ancient sites, McLaren, Fedje, and their UVic colleague Quentin Mackie have spent decades mapping the local sea level changes along the coast of British Columbia. On Calvert Island, where the footprints were discovered, sea level rose only 2 meters. Around nearby Quadra Island, local sea level actually fell, stranding ancient shorelines in forests high above modern beaches. There, "potentially the entire history of occupation is on dry land," Mackie says."
     
  13. Dec 4, 2017 #12
    Please clarify your point.
     
  14. Dec 5, 2017 #13

    Tom.G

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    I took your "No way!!" as declaring that local sea level could not drop when an Ice Sheet melts, under any circumstances at all; or absolutely could not happen. I provided a counter-example.

    One definition of absolutism is: "doctrine of absolute decrees." Admittedly, the word is more often associated with political or religious concepts. So, yes I did stretch its use a bit.

    This side discussion could be hinging on the definition of local sea level. A rather common usage (which I assumed) is the relationship between the local land and the local water level. Another interpretation could be the local water level in relation to the center-of-mass of the Earth. So it seems we could both be correct! If you choose to continue this discussion, let us do so using the Conversation facility so we don't further clutter this thread.
     
  15. Dec 5, 2017 #14
    Ah, you misunderstood me then, it simply was meant as an exclamation of how cool and counterintuitive it was.
     
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