Ponzi 2: What year will coastal property values crash?

[JR: Please Digg this post by clicking here.]

Coastal property values won’t wait to (permanently) fall until sea levels have actually risen 4 or 5 feet, as they almost certainly will by the end this century on our current CO2 emissions path (see Startling new sea level rise research: “Most likely” 0.8 to 2.0 meters by 2100 and Report from AGU meeting: One meter sea level rise by 2100 “very likely” even if warming stops?).

Coastal property values will crash when a large fraction of the financial community and of opinion-makers — along with a smaller but substantial fraction of the public — realize that it is too late for us to stop 4 to 5 feet of SLR. And remember, if we don’t get on the sustainable sub-450-ppm path soon, then people will quickly come to understand that SLR won’t stop in 2100. Seas will continue rising post-2100 perhaps 10 to 20 inches a decade (or more) for centuries until we are ice free and seas are 250 feet higher. And that makes protecting most coastal cities very, very difficult and expensive.

One of the points of my post “Is the global economy a Ponzi scheme and what comes next? Part 1,” of course, is that we haven’t hit that critical mass of knowledge yet. If we had, the world would be engaged in a massive, desperate effort to avert catastrophe.

And so I pose the question in my talks: What year will coastal property values crash?

I am certainly interested in your thoughts on this.

I pose the question mostly to stimulate thinking. And certainly the collapse is unlikely to happen in just one year — so perhaps the better question is, What year will U.S. coastal property values peak?

I tend to think the peak comes some time in the 2020s.

The peak will probably be linked to one or more major climate disasters of a kind that I enumerated in “What are the near-term climate Pearl Harbors?” Note that the growing fear of a hurricane damage has already been made getting new insurance for coastal homes in places like Long Island difficult (see here).

But awareness on SLR is growing (see US Geological Survey stunner: Sea-level rise in 2100 will likely “substantially exceed” IPCC projections). And it is poised to grow even more quickly in the coming years, as yesterday’s article in UK’s Guardian newspaper, “Scientists to issue stark warning over dramatic new sea level figures” makes clear:

This week’s climate change conference in Copenhagen will sound an alarm over new floodings — enough to swamp Bangladesh, Florida, the Norfolk Broads and the Thames estuary.

Scientists will warn this week that rising sea levels, triggered by global warming, pose a far greater danger to the planet than previously estimated. There is now a major risk that many coastal areas around the world will be inundated by the end of the century because Antarctic and Greenland ice sheets are melting faster than previously estimated.

Low-lying areas including Bangladesh, Florida, the Maldives and the Netherlands face catastrophic flooding, while, in Britain, large areas of the Norfolk Broads and the Thames estuary are likely to disappear by 2100. In addition, cities including London, Hull and Portsmouth will need new flood defences.

“It is now clear that there are going to be massive flooding disasters around the globe,” said Dr David Vaughan, of the British Antarctic Survey. “Populations are shifting to the coast, which means that more and more people are going to be threatened by sea-level rises.”

It certainly bears repeating that it is not too late to prevent the worst, were humanity to engage in an all out effort to stay below 450 ppm, but time is running out for that option very quickly.

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44 Responses to Ponzi 2: What year will coastal property values crash?

  1. Linda S says:

    We live on a barrier island in the Gulf of Mexico. Our island was hard-hit by hurricane Ivan back in 2004. About half of the property in our neighborhood has been for sale ever since. As far as we’re concerned, peak was 2004 and it wasn’t a downward slope, it was a cliff.

  2. Danny says:

    I think the real question is where will coastal property values crash first, and in which significant urban areas will they crash first? For example, Bangladesh may be flooded before New York or even Amsterdam, but the impact on the wealthier Western nations will be marginal, as compared to, say, most of urban Florida getting flooded. And that will be something people are less likely to ignore. So which major urban centers in the West will be affected first?

  3. paulm says:

    May be we should have a campaign to convince some of these weather men that they need to be more responsible about climate change…it seems to work on Senators.

    Veteran Meteorologist Bravely Calls It Like He Sees It

    How ironic that one of the last of the dying breed of global warming deniers in America is welcomed into our family home every night. They’re your local TV weathermen (yes, mostly men) who despite their careful tracking of weather disasters and trends are hell bent on denying that global warming is happening.

  4. Considering that almost half of the US (according to census data) lives within 50 miles of a “coastal area” subject to flooding, any change in sea level would quickly affect a large percentage of the population. Although it may be difficult to discern the impact of SLR on coastal property values amidst tumbling real estate markets, it IS reasonable to note the long-term implications of stablizing properties in coastal areas vs those on ‘higher ground’. We have been economically driven into an opportunity to alter our behavior both environmentally and geographically, I hope we proceed wisely.

  5. DB says:

    “I tend to think the peak comes some time in the 2020s.”

    2020 (eleven years from now?!?) is probably too soon, as the probabilities for the next decade have to include the temperatures not rising much because of natural decadal cycles such as the PDO. See, for example, the Keenlyside paper.

    Advancing decadal-scale climate prediction in the North Atlantic sector
    “Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.”

    This situation would delay the price peak to 2030.

  6. paulm says:

    It certainly is peaking now. And it looks like the realization of this outcome will certainly happen in the next couple of years.

  7. ken levenson says:


    (the projected rise has grown exponentially over the last several years….what’s to stop it?)

  8. Sasparilla says:

    I think your date sounds about right Joe – at that point effects should be so blatant that we’ll finally might see larger portions of the population move into “we better fix this mode”.

    Unless the market does it somehow ahead of time (no insurance at all for coastal properties). Otherwise when this happens will probably be about when overpowering majorities here in the US starts seeing this a real crisis we actually have to address (not just another problem that we can wishy wash our way though) – in the 2020’s sounds about right, unfortunately, another generation hence.

    Our current US political system (Senate) isn’t up to saving our future for the time being.

    Its too bad Osama Bin Laden (or some terrible dictator) wasn’t inflicting global warming/climate change/climate chaos on us – we would be having a war on it and winning, right now, it would be a piece of cake politically.

  9. P. G. Dudda says:

    I don’t think sea levels will rise enough to make a serious difference for the USA till at least 2030, possibly even 2040, so I’ll split the difference and say 2035. Other countries, like Tuvalu and Maldives, will probably start evacuating by 2025, though…

  10. Florifulgurator (Germany) says:

    Oh the funny picture of London! They can re-use the wheel for electricity production and water pumping.

  11. paulm says:

    Any one interested in owning some potential scuba diving property…going cheap.

    You’ll be able to keep your pet shark and various other marine life in their natural habitat.

  12. tidal says:

    When are they GONNA peak? They peaked well over a year ago. As Austin Powers puts it, sadly, that train has sailed!

  13. Jock Gill says:


    From these first two posts on the Ponzi Scheme theme, a description I have been using for over a year now, and from Friedman’s article yesterday, I deduce that you agree that any and all attempt to “re-boot” the infinite growth Ponzi scheme will not only fail but are, actually, pathological. So what does this say about the sages in Washington and Wall Street who are desperately seeking a simple reboot? The cold reality is that we need an entirely new operating system on a new motherboard. I wonder if we have the time left to develop both and bring them to global scale?

    [JR: Sadly, the US political system operates within the boundaries of what is possible as defined by opinion makers, the media, and a pathologically obstinate but still potent political minority. That said, it is not possible to imagine a more informed or persuasive group than Obama, his cabinet, and advisors. So if the US political system can be moved to take a leadership position, we will soon find out.]

  14. paulm says:

    The depression is probably a god send…she’s helping us along in the necessary restructuring of society and at the same time reducing CO2 at a critical time.

    There was no way that the west was going to move to a sustainable structure with out sock and awe. Life was too comfortable.

  15. caerbannog says:

    I have worked out a strategy for my coastal San Diego condo.

    I’m about 65 feet above sea-level and directly under the Lindbergh Field flight-path.

    I figure that when sea-levels rise 5-6 feet, the Lindbergh Field runways will be flooded
    at high tide. This will greatly reduce the aircraft noise, and I should see a nice jump
    in my property values.

    At 10-12 feet, I’ll be on an island (Isle de Loma as opposed to Point Loma). Access problems could raise havoc with my property values, but I’m hoping that the exclusivity of living on an island will offset that.

    At 60 feet, I’ll have a nice little private inlet behind my place. At that point, I’ll hire a contractor to build a boat dock and invite a super-rich type to park his yacht there.

    Then I’ll put the place on the market (oceanfront condo with private boat dock) and hope to sell the place before salt water starts soaking my carpeting.

    Of course, this all presumes that I’ll live to be 300 or so….

  16. paulm says:

    Depressing article in Independent…

    Carbon cuts ‘only give 50/50 chance of saving planet’
    As states negotiate Kyoto’s successor, simulations show catastrophe just years away

  17. DB says:

    “Carbon cuts only give 50-50 chance of saving planet”

    And that is with cuts that aren’t even on the table according to the article:

    “At the moment, global emissions are thought to be rising at nearly 3 per cent a year – so turning that into a 3 per cent annual cut would be a gigantic slashing of what the earth’s factories and motor vehicles are pumping into the atmosphere. There is as yet nothing remotely like that on the table for potential agreement in Copenhagen”

  18. hapa says:

    what the money crash has done, following the iraq invasion, is demonstrated the reckless dogmatism and instant cupidity of the decider class. people looking at their “let compound interest tackle nature’s needs” approach with any objectivity ought to be disgusted. but the mechanisms for getting organized and starting the next way of doing things are not in place. our systems are sclerotic with debts and overcomplicated dependencies.

    i see this as ironic — remember that study showing that ice sheet behavior may be non-linear? what’s going to break, how, among the body politic, may be the same here. glacier, until flood.

  19. Andrew says:

    I live in the Houston/Galveston Area which is a unique in the world test case for the beyond the worst case sea level rise scenarios. Starting in the late 1960’s groundwater pumping caused coastal lands to begin sinking at rates up to 1′ per year!!! Total apparent sea level rise was up to 15′ in places. Whole subdivisions were submerged as was a tremendous amount of infrastructure. The beaches at Galveston were far enough away such that they only suffered 1-2′ of apparent sea level rise, though this means the beach is migrating inland at a clip of about 10′ a year.

    Some folks know how fast the “water is coming up” and plan for it. They buy a house a ways in from the Gulf knowing it has a limited life time. Or some folks haven’t got the word and are suprised when their home falls into the ocean. Or a lot of folks can’t afford to live anywhere else and live in rental properties that flood with every high tide.

    Over the years the inexorable march of the ocean inland has meant that realestate prices will never reach the levels seen on more stable coastlines and that Galveston, for example, if often thought of as a third world country (that’s from a BOI, born on island friend of mine so don’t yell at me for the description). But nothing, nothing is abandoned until it’s litterally out in the ocean. In fact, some homes have walkways to them out over the surf while the State battles them in court in an attempt to condemn the property; a many years long process.

    The decline in coastal land values will be a slow, punctuated process whereby values stay steady or even rise a bit before a storm causes them to drop sharply and recover partially. High coastal lands will increase in value as that of lower areas declines. Slowly, local governments of low lying towns will fail and after a long time the community will be abandoned to folks who are willing to live in trailer homes on stilts with no services. That’s what’s happening in Texas and Louisiana where the land has been sinking and the sea apparently rising for the better part of a century now.

    When will it this realization be broadly accepted? I’d say not until 2060, when the eustatic sea level has risen 2′ over today’s level.

  20. hapa says:

    also predictions of property values will depend on public policy choices (including watershed management and housing subsidies along with insurance) and of course the actions of private insurers. without deep stomachs for risk in investments, prices for risk on the insurance side should rise.

  21. Joe what a wonderful discussion.

    Sea level property values are now short term investments. Another Ponzi scheme. Who gets to own the property last?

    Our time has been the very best time to be alive, the very peak time for humans, certainly.

    Now starts our species decline and/or the beginnings of a new species. Very interesting times from now on. Happy to be here. This is the peak.

    Peak Human genome maybe now, or 2050 – toxins and viruses will mess things up after that. Any survivors will be a new species.

    Peak Global biological diversity 1700 –

  22. DB says:

    “Peak Global biological diversity 1700”

    FWIW, the time of maximum diversity (corrected for sampling) was probably back during the Cretaceous, some 90 million years ago.

  23. Dean says:

    Contagion is the word that applies to most things financial. The time that this issue “hits” will likely not relate too much to how much the sea has actually risen at that point in time. It may not hit in specific coastal locations most at risk. It will require some public event that galvanizes public opinion, like a run of extreme weather events of some type, particularly heat waves or droughts (is it possible for a major warming-caused ice sheet collapse to cause a tsunami?), and some public figures not previously tied to the issue making some public declaration or indication that they are selling. And anybody who tries to guess it will probably be wrong. This has as much to do with the herd mentality of finance as the science of climate.

    I want to know when the southwestern droughts will cause housing values to plummet (again?) in Phoenix and Las Vegas. I’ve been telling a friend who owns retirement income property in Phoenix not to wait too long.

  24. ecostew says:

    It may be that mortgage/insurance entities will start not lending/ensuring if one is in the 100-year predicted to be new sea level zone. They could be mapped and updated quite easily.

  25. Coo says:

    After Katrina, I researched and wrote a report on damage to a segment of utility infrastructure. A few items of note:
    –Damage from rising sea levels will happen during storms, when storm surge will be ever higher.
    –Katrina storm surge (of 10-22 feet, I believe, and I saw much of it) hit a 250-mile-wide swath stretching from the western edge of Alabama, across Mississippi, and well into Louisiana. The entire coast line of Mississippi had a debris field 500 yards inland (see NOAA satellite images here: ). No one knew it because a high tide caused by a hurricane is termed Storm Surge; if from an earthquake, it’s called a Tsunami. No difference in infrastructure damage, big difference in media coverage.
    –This damage happens all the time, but in smaller areas of usually five-to-ten miles along a coast line. (As an aside, reinforced concrete structures are about the only structures to survive.)
    –Currently, local areas rebuild. But as this continues, the cost will become prohibitive. Insurance is already a problem, and one more Katrina will probably seal that fate. But the poor will remain in these regions, as the coastal areas are beautiful and housing will become cheap, if not very nice (for an example of where this is already occuring, visit Plaquemines Parish, LA, where there are many jobs supporting the port. All homes were lost during Katrina, but I’m betting there are many people living there again).
    –Populations will slowly decline in most areas, as people leave only reluctantly. The cost of maintaining services across a smaller population (and tax base) will be prohibitive. States and developed countries will have to regionalize services to spread the costs of infrastructure replacement (or mitigation and adaptation) across a greater number of people. A significant decline in services is likely, especially in developed countries, where we have farther to fall.
    –We have massive investment in infrastructure (buildings, transportation, ports, water and wastewater, power, telecom, etc) along the coasts and across entire countries in low lying regions. We cannot simply leave these investments, as much of this infrastructure is linked. We didn’t build it out based on altitude and we still aren’t. Wealth destruction over the next century will be appalling, as will the environmental impact.
    –Human suffering will be severe, particularly in Asia, and that will further hamper our ability to address the economic issues.
    –We are still wimps. No one talks about the inability to support current and projected population levels.
    Sorry to be so negative but I read Calculated Risk’s February Economic Summary today.

  26. greg says:

    is there a way to short sell real estate?

  27. Greg Robie says:

    In a lighter vein (with an interesting link), the same year that the government does not insure ocean front property, , and that will be, lets see, the same year that girls stop looking great to the opposite gender in their swim ware (or not)?

    ”Well, with two swingin’ honeys for every guy
    And all you gotta do is just wink your eye

    “Ya, we’re goin’ to Surf City, ’cause it’s two to one
    You know we’re goin’ to Surf City, gonna have some fun
    Ya, we’re goin’ to Surf City, ’cause it’s two to one
    Ya, we’re goin’ to Surf City, gonna have some fun, now
    Two girls for every boy”

    Oceanfront property, or is it what goes there to catch the sun, has such an allure . . .

  28. TomG says:

    Yeah…I’ll go with the 2020’s.
    But I noticed you said all US coastal property, not just the low Gulf Coast and Florida. Those guys are going to get a double whammy….higher water and more intense storms. These properties will lose their value much quicker…

  29. jorleh says:

    Business as usual is going to destroy our possibilities not to go over ppm 450, and 550, even 1000.

    We have these Lomborgs and Inhofes enough to stop any science to get heard before 2020, and it´s too late then.

  30. Greg Robie says:

    On a serious note, the query is part of the paradigm that cannot survive in the paradigm that insures survival.

    For example, Manhattan was not “sold” for $24 in trinkets, only the right to share it was agreed to by one of the parties involved in that transaction. In a paradigm that insures survival, one can only “own” (in a Western sense) that which you can take with you at death. Last time I checked that amount out, it wasn’t very much in terms of property/wealth.

    Consequently (and logically), the other party of the above “sale” is non-rationally stuck in a paradigm that trusts (finds comfort/oxytocin) in the ownership of private property. It is lost to the delusions of its socially agreed on motivated reasoning.

    If survival of homo sapiens is held as a moral tenant, thinking that property has any value that can collapse is irrational thinking. This is true whether it is in terms of ownership, or holding or “investing in” mortgages, or allowing a currency “coined” in such debt to be the bases of ones economic interactions.

    In a sustainable paradigm, beyond owning the responsibility of stewardship for property that is lived upon; that a living is derived from, no other ownership is rationally possible. Therefore, the date we become rational in our knowing as homo sapiens is the year oceanfront property “values” collapse . . . the 12th of never?!?

  31. cait says:


    On a related but not directly question:

    Presumably there has been some research done on the de-salinisation of the oceans as they increase in volume with dissolves fresh water ice. Are there any guesses as to what the levels of change are / what that will do to the salt water fish stocks?

    Note: I am not talking about the changes that are eg: affecting coastal reefs right now. Specifically talking about whether the volume of fresh water entering the oceans will actually affect it enough to make any difference (given the vast volume of salt water on the planet in the first place).

  32. Ray says:

    Hey cool….What a deal I have for you! I live @ 5800 ft elevation, high enough to remain dry regardless of what sea levels do, far enough inland to not be overwhelmed by the soggy masses as they retreat. 15 acres, a shop, garage, a very nice custom two level house with a huge tree covered yard.

    Trade straight across for equal layout on the coast of Oregon or Wash. I would also consider a south pacific island. This offer does not extend to property in Calif.

  33. Lou Grinzo says:

    This is going to sound very cynical and unkind, and I sincerely apologize for that in advance.

    I think that our capacity for self-delusion will reach new heights on this topic in the coming years and decades. Say, for example, we have the Hurricane Season From Hell, and New Orleans and/or Houston get smacked several times in a single season. The human loss and suffering, the economic impact, are vastly greater than Katrina. Major news magazines run covers with headlines like “Eco-Holocaust” and “Apocalypse This Summer”.

    What will happen? The rest of the country will, for the most part, shrug it off. We’ll watch the reports on TV and online, donate money to the Red Cross, but it will largely be a “there” problem for the overwhelming majority of Americans, not a “here” problem. The mostly unspoken undercurrent will be a feeling that these people were dumb enough to live in such an area, so they shouldn’t be surprised at what happened. After all, look at the storms that hit those areas “years ago”, right after 9/11, wasn’t it?

    Major storm damage in South Florida would elicit much the same half-feeling response from the rest of the country: “Sucks to be them” and a shrug.

    Even if one of the less-talked about scenarios played out–a killer storm runs up the East Coast and hammers Washington or NY City (as one cut a swath through Long Island in the early 1900’s), it wouldn’t make a big difference, as it would be seen as a freak occurrence.

    The only impact that would dramatically affect coastal areas across the US would be enough SLR to cause huge losses in multiple cities. The denierbots would still do their best to tell people it was nothing to worry about, but the (vast?) majority of Americans would (for once) ignore them.

    I hope no one thinks that I’m in any way saying this “sucks to be them” indifference is a response I have or that I would in any way approve of; if such a terrible turn of events were to happen, I would be deeply ashamed of many citizens of the country I love. But I’m convinced that this is the most likely response to such a storm scenario.

  34. Greg Robie says:

    The oceans currently have different salinities and salinity zones. These will change with ice melt, but given the mixing that goes on with ocean current macro dynamics, such as the great ocean conveyor, unless it stops, changes will likely be gradual enough for species to adapt to the change. In addition, fresh water is less dense that salt water. It floats on top of the salt until it is mixed in via micro currents and thermal incline transfer dynamics.

    Marine fish stocks are already threatened by overfishing, and dead zones. Sea level rises will disappear estuary systems and salt water marshes. These are the nurseries of much of the oceans’ marine life. The study I would like to see is what a 5′ sea level rise does to these nurseries and what remains of the balancing dynamic that supports the marine ecosystem (if we do not fish the oceans empty before these nurseries are submerge and lost.

    BTW, these nurseries are also highly effective carbon sinks. Losing them is another positive feedback. Recreating them, dynamically, with sea level rise is another labor intensive ongoing miracle that will be a desired social endeavor that we are not thinking or feeling about yet.

  35. Greg Robie says:


    The point you make is morally sobering, but our collapsing economy may cure us of the infection of individualism’s meme. If so, things may not play out as you posit. Regardless, we are much more interdependent that we feel we are.

    To back this up consider that a strategic study was done by the military at the outset of the nuclear age. It purpose was to determine how many atomic bombs were needed to destroy the Soviet Union. That study, hosted at MIT (BTW, Joe), determined that the social chaos that would be effected with five major urban centers experiencing a nuclear explosion would be sufficient to destroy the Soviet Union capacity to function as a society. Does such logic apply to us/US today?

    Katrina packed the wallop of a nuclear bomb. $80 billion in Federal aid and all that has been pumped in from other levels of government, charities and volunteers did little more than wobble the economy of the time. Even so, had Rita leveled Houston, had Miami been hit, Philly, NYC, Boston (I won’t list DC, for loosing it would be a blessing), throw in a major drought event, and the big one out west, and that would wake us up from the illusion of our separateness long before such a check list is checked off by mother nature.

    Regardless the economy that barely wobbled is gone. It is not coming back (no matter how much the hope of the bright and light greens; no matter how strong the denial of the grays). Mother nature holds the trump card of global warming and it has been played. We are on a fast track for learning things we have long considered unimaginable. Our denial of our interdependent is being shattered. The homework this lesson assigns us is figuring out whether we will choose to respond violently or non-violently. Your own despair gives me hope. It suggest that your desire to be compassionate will trump you cynicism when push comes to shove. The volunteer response to Katrina supports such a hope as well.

    Robert Fulghum, in his book, _All I Really Needed to Know I Learned in Kindergarten_, listed, as one of those things, to hold hands when crossing the street. It is a hell of a street that we have to cross. We may not make it across. But if we hold hands while trying we will demonstrate that as sapiens we have the capacity to learn anew what we know; what is the best that makes us human.

  36. papertiger says:

    If a for profit wind energy hack is to be trusted , then I’ll have to move my beach towel in about 11 years, instead of going by the best evidence which suggests it can stay where I left it for another hundred.

    Ah what the heck. I feel like living dangerously. Life is too short to go through it without a spine.

  37. Ella K. says:

    I think the H2Os are going to be here earlier than 2020s.
    Once the temps increase beyond a certain threshold, NO ONE knows how all the ice packs will react.
    You know the Anderson Ice shelf that caved in the Antarctic a couple of years ago, they had predicted it would take 100 years for it to melt and satellite pictures showed how it took a couple of months or so, from when the cracks appeared in it until it was all gone!That was the most horrifying moment for me and the fact that it virtually got no publicity was even worse!
    I have had nightmares of BIG waters for over a decade now( thought that this was due to the fact that I cannot swim to save my life), but I have finally put it together!
    Those waters are closer to us than we think!!

  38. The Peak Was 2006 says:

    Joe, we overemphasize the “flooding.” It’s the salinization of our adjacent lands, water tables, estuaries ….It’s the breakdown of the balance that quells pests and viruses … People don’t understand that IT AIN’T JUST THE BEACHFRONT PROPERTY!

  39. Dick C. Flatline says:

    What’s with all this negativity? As a hardcore sportfisherman, I personally look forward to (a) a shorter drive to the Gulf, and (b) the ability to refer to Florida’s coastal cities as “incredible structure”. I’d rather see Tampa filled with redfish than with crackheads and rude tourists.

  40. Diane Trout says:

    A BBC documentary “Britain from Above” had a segment on a village that was abandoned because the coast is disappearing at the rate of 40 feet per year.

    During the clip the reporter was told he could probably buy one of the houses for £1

  41. John in Portland Or. says:

    South Florida would seem to have it the worst… most of it to disappear. All of this talk of flooded coastal lands brings to mind the great dikes of the Netherlands. But its said that the time line for projects like this would be 30 years and at astronomical cost… And where dikes and levies may work for certain parts of the country, not so for sunny south Florida where the entire region is said to be built on a bedrock of porous limestone. It drains very nicely after a storm… and will conduct sea water freely under any barrier as sea levels continue to rise…