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Don Paul: With global warming come 'sunny day floods'

Don Paul

We have our own regional water level problems, which ebb and rise cyclically, as is currently happening along the shore of Lake Ontario.

There is a tenuous link between climate change and lake levels (more heavy precipitation events tied to a warming atmosphere over recent decades sending more runoff into the lakes). The cyclical nature of lake levels, however, was with us prior to accelerated mean global warming.

What are “sunny day floods?” The phrase refers to flooding which now occurs more regularly at high astronomical tides, along large stretches of the east coast and and some parts of the Pacific coast (as well as on other continental coasts). This kind of flooding is not storm-related and often occurs on bright, sunny days. It is directly related to mean global warming and its causally connected glacial ice melt with their production of steadily rising sea levels. In other words, this phenomenon didn’t occur when sea levels were lower, prior to the ongoing warming. This is what it looks like:

Some of the explanation offered by a Miami spokesperson in this AP video is a little garbled, but the video speaks for itself. It’s not confined to the east coast. Here is Longboat Key video from the City of Sarasota, on the west coast:

Despite these Florida videos, the greatest sea level rises on the east coast have occurred farther north, from North Carolina up to New Jersey. In that area, in addition to sea level rises due to ice melt and expansion of water volume due to warming oceans, there is another factor called “glacial rebound.” Since the last ice age maximum 26,000 years ago, the weight of the ice fields which retreated north has been lifted from the middle Atlantic seaboard, allowing the sea bed to “rebound” upward as detailed in Woods Hole Oceanographic Institute research.

Sea levels in this zone over the last century have averaged a one and a half foot rise, as opposed to about a foot near New York City and New England and Florida. This tidal flooding becomes acute at the highest astronomical tides with the alignment of the sun and moon maximizing gravitational tug on the waters. These tides are often called King Tides.

As we see even in just examining the east coast, sea level rises are not uniform globally. There are even a few small spots where the rise is not occurring due to upwelling cold bottom waters. But the mean global rate of rise is a little more than 3.3 millimeters per year, with levels derived from precision satellite and ocean buoy data.

Some coastal locations have geologic problems unique to the region. State and federal data suggest the greatest coastal land submersion in the U.S. is and will be occurring in Louisiana.

Louisiana’s vulnerability is exacerbated by land subsidence/sinking and soil erosion, combining with rising sea levels for a double geologic whammy.

Miami Beach has a mean elevation of just 5 feet above sea level. Worse, the city sits atop porous limestone which fills with sea water at high tide. This water comes bubbling up through drains farther inland, and normal land drainage into the sea is blocked by the rising waters’ resistance to outflow. So, towns and suburbs located further from the coastline are also experiencing sunny day flooding with gurgling waters coming up through drainage pipes and gratings.

The most acute threat for now, however, is at the sea’s edge. Yet, Florida realtors report land and property values on the water are still skyrocketing, even in the face of already serious high tide flooding, not to mention occasional much worse storm surges from tropical cyclones. This from TheRealDeal, a South Florida newsletter for realtors: “Meanwhile, residential prices and sales in coastal markets in the U.S. are on the rise. In Miami Beach, luxury home sales increased more than 60 percent year-over-year in the fourth quarter of last year. Home sales in Nantucket, a small island off Cape Cod, Massachusetts, rose 161 percent in 2018 compared to the previous year. And in the barrier islands off the coast of North Carolina, the average sale price rose 11.5 percent over the last three years, according to Bloomberg.”

The realtors report insurance costs are being kept artificially lower than you might expect by subsidizing capital, to keep the market strong. One Miami realtor said on a video that not one of her prospective clients even brought up the subject of coastal flooding. It’s not as if such clients could be unaware of the risk. It’s publicized widely and frequently.

Miami Beach has committed to spending $400-500 million to raise street and land levels by up to 2 feet, to keep the resort and residential center active and growing. Such mitigation efforts will bear some fruit, at great cost, but mainly for people alive now out to as far as, maybe, mid-century. Inevitably by the end of the century, rising sea levels and impacts will breach these buildups. The more costly mitigation structures proposed by former Mayor Michael Bloomberg to protect New York City, its harbor, and the nation’s fiscal center could mitigate impacts longer. Floodgates and barriers will cost many billions, but the costs from loss of large tracts of the New York metro area and Wall Street, as well as residential regions would be almost immeasurably greater than the cost of the mitigation structures.

In the meantime, here is something for current and future waterfront transplants to think about. Even if there is a surprisingly successful slowdown in our rate of warming oceans and atmosphere, sea level rises are not going away. There is a huge difference between how much they rise if we do almost nothing to reduce fossil fuel usage versus more aggressive reductions. But waterfront property will become riskier and riskier this century. It’s going to be a question of magnitude. This video from Harvard University tells a basic story:


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