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Earth Science

Florida Keys Prepare For Sea Level Rise 101

Posted by Soulskill
from the good-excuse-to-get-out-of-florida dept.
An Associated Press report details how the Florida Keys are starting to prepare for seasonal flooding and rising water levels overall. "A tidal gauge operating since before the Civil War has documented a sea level rise of 9 inches in the last century, and officials expect that to double over the next 50 years." Flooding used to be a much rarer occurrence, but now many businesses are finding it necessary to have plans in place to deal with it. "The Keys and three South Florida counties agreed in 2010 to collaborate on a regional plan to adapt to climate change. The first action plan developed under that agreement was published in October and calls for revamped planning policies, more public transportation options, stopping seawater from flowing into freshwater supplies and managing the region's unique ecosystems so that they can adapt, too." The Keys are one of many places beginning to seriously evaluate their options for dealing with flooding after witnessing the damage caused by Hurricane Sandy.
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Florida Keys Prepare For Sea Level Rise

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  • perspective (Score:5, Informative)

    by stenvar (2789879) on Wednesday July 03, 2013 @12:28AM (#44173205)

    To put this into perspective:

    http://en.wikipedia.org/wiki/Florida_keys [wikipedia.org]

    The Florida Keys have taken their present form as the result of the drastic changes in sea level associated with recent glaciations or ice ages. Beginning some 130,000 years ago the Sangamonian Stage raised sea levels to approximately 25 feet (7.5 m) above the current level. All of southern Florida was covered by a shallow sea [...] Starting about 100,000 years ago the Wisconsin glaciation began lowering sea levels, exposing the coral reef and surrounding marine sediments. By 15,000 years ago the sea level had dropped to 300 to 350 feet (110 m) below the contemporary level.

    The Florida keys are an environment that's neither stable nor safe from flooding, and when you live near the water, you have to live with the fact that you need to move sooner or later. Even without anthropogenic warming, there would have been substantial sea level rise over the last century, and these precautions would be necessary and prudent.

  • Re:perspective (Score:5, Informative)

    by garyebickford (222422) <gar37bic.gmail@com> on Wednesday July 03, 2013 @01:13AM (#44173349)

    I don't know the specific geology of the Keys, but most places with ocean interfaces are either raising or lowering with respect to sea level. For an example of short term movement, the shore of Japan close to the quake and tsunami in some cases is feet lower than it was before the quake because as the pressure built up over centuries, that land bowed upward, and when the stress was released the land dropped again. And on the Oregon coast there is a shallow marsh that before January of 1700 was a cedar forest, but it dropped six feet in that earthquake.

    Other areas are dropping or rising more gradually. Many Pacific islands would be gradually going under water over the next few centuries regardless of the global sea level change.

    Basically, the entire surface of the Earth is a bunch of scum piles being shifted around on an ocean of semi-liquid material, bumping into each other and tilting in various ways. As the Asian and Indian Ocean plates collide and tilt up to form the Himalayas, the other ends of those places are dropping. And there is now evidence that the Atlantic plate is cracking in the middle, offshore of Portugal because of similar activities.

  • Re:perspective (Score:5, Informative)

    by Anonymous Coward on Wednesday July 03, 2013 @04:13AM (#44174049)

    ...the entire surface of the Earth is a bunch of scum piles being shifted around on an ocean of semi-liquid material, bumping into each other and tilting in various ways

    Generally, yes, but that ignores the fact that there are no plate boundaries nor obvious tectonic processes operating within any distance of the Florida Keys that can account for more than the most inconsequential sea level change over the last 150 years. In short, the keys are tectonically stable. A nine inch in rise in sea level over the last hundred years or so is consistent with the change in global sea level over the same period.

    More generally, many ocean/continent boundaries are active margins, but far from all of them. Consider as counter examples the east coasts of North America and South America, the west coasts of Europe and Africa (despite evidence for incipient subduction off Western Europe, as it certainly doesn't currently dominate tectonic regime there), three sides of Australia, the east coast of Africa, the entire coastline of Antarctica, the northern coast of North America along the Arctic Ocean, and most of the northern coasts of Asia, are all passive margins. These areas as not devoid of tectonic activity, but it's usually mild compared to areas around the Pacific Ocean and other active continental margins.

    It may also be worth observing that some parts of the world, especially Northern Europe and parts of North America, even where the tectonic environment is mild, are still isostatically rebounding upwards following the last glacial maximum. The ice sheets were so massive that they depressed the continents underneath them. Now that the ice has melted, the land is slowly rising back up from the viscous mantle upon which the continents float. In those places, with the land rising, local sea level may be falling. Isostasy can also locally affect other areas where there's a lot of geographic relief, such as in high continental plateaus where erosion unloads the land surface, or where high relief upstream contributes large volumes of sediment. The Florida Keys are not, however, subject to these processes.

    The global average sea level, or sea level measured against an artificial reference point, is called eustatic sea level. Over hundreds of millions of years tectonic processes can affect eustatic sea level, but on shorter time frames the tectonic variation averages out: if rock is rising in one place, it's falling in another, so the contribution to sea level changes by tectonic processes are generally only local. For example, the sea level in the Florida Keys won't be affected by changes in the local sea level along the coast of Japan.

    The biggest general contributor to most sea level change on the timescale of our species is climate, not deeper geologic processes. There is a minor component related to the thermal expansion of seawater, which accounts for probably about half the currently observed sea level rise, but the dominant longer term factor is variation in the amount of ice sequestered in continental ice sheets -- like the those that once covered much of North America and Europe, as well as the extant Antarctic ice sheets and Greenland Ice Sheet. Broadly speaking, throughout geologic history the amount of water impounded in continental ice sheets will tell you more about eustatic sea level than any other single factor. Back through the Pleistocene, if you had to guess how much water covered any random point on the globe, knowing the level of glaciation would on average give you a better answer than anything else. Sea level tracks very closely with glaciation.

    You can look at the Greenland Ice Sheet as a remnant of the much larger Pleistocene ice sheets in the northern hemisphere during the last glacial maximum. The Greenland Ice Sheet contains enough water that if it were to melt or flow in to the ocean, eustatic sea level would rise a couple dozen feet even without contributions from other reservoirs. Since the late Pleistocene, eustatic sea level has ris

  • by Thud457 (234763) on Wednesday July 03, 2013 @08:43AM (#44175741) Homepage Journal
    It's all about the storm surge
    two thirds of Key West was underwater during Wilma [google.com].
    That used to be a once in a generation thing. Then it's going to be every 20 years. Then every 5. Even if it doesn't turn into New Atlantis, that's gonna put a real crimp in the island lifestyle.

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