Guest Essay by Kip Hansen
In remembrance of the victims of Hurricanes Harvey and Irma: I have held off publishing this essay until after the damage from Hurricane Irma could be determined hoping not to add to the fears, angst and now sorrow experienced by both victims and their relatives. My prayers and sympathy go out to all who have suffered losses.
Sea Level Rise: Is it the greatest threat the posed by Climate Change today?
The press tells us it is:
“The current best estimates predict that sea level will rise up to 6.6 feet, or 2 meters, by the year 2100.” — The Climate Institute, “Sea Level Rise: Risk and Resilience in Coastal Cities” by Erin A. Thead
“A rapid disintegration of Antarctica might, in the worst case, cause the sea to rise so fast that tens of millions of coastal refugees would have to flee inland, potentially straining societies to the breaking point. Climate scientists used to regard that scenario as fit only for Hollywood disaster scripts. But these days, they cannot rule it out with any great confidence. The risk is clear: Antarctica’s collapse has the potential to inundate coastal cities across the globe. … If that ice sheet were to disintegrate, it could raise the level of the sea by more than 160 feet — a potential apocalypse, depending on exactly how fast it happened.” — The NY Times, Looming Floods, Threatened Cities, a three part series by Justin Gillis
But is it, really?
“Sea level has been rising for the last ten thousand years, since the last Ice Age…the question is whether sea level rise is accelerating owing to human caused emissions. It doesn’t look like there is any great acceleration, so far, of sea level rise associated with human warming. These predictions of alarming sea level rise depend on massive melting of the big continental glaciers — Greenland and Antarctica. The Antarctic ice sheet is actually growing. Greenland shows large multi-decadal variability. …. There is no evidence so far that humans are increasing sea level rise in any kind of a worrying way.” — Dr. Judith Curry, video interview published 9 August 2017
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Sea Level Rise (SLR usually hereafter) is being characterized in the press — newspapers, magazines and television reports — as the latest and greatest threat to mankind from human-caused climate change.
Why? It is always difficult to assign motivation to social memes but it is not disallowed to speculate. The Global Warming threat has lost much of its appeal with the general public — air temperatures simply have not risen as threatened 30 years ago by James Hansen, despite the changing metrics used to measure and promote it, and, quite frankly, it no longer looks like they are going to. I needn’t repeat the story of IPCC model prediction failures and the shortfall of actual global temperatures to match their alarming projections. As we know, the public face of Global Warming shifted from Dangerously Rising Air Temperatures to Climate Change (including Extreme Weather, and Sea Level Rise) over the last 20 years — though the scientific community has always used both terms interchangeable (for the most part). But we see fewer magazine covers featuring a flaming Earth — instead we more often see images super storms and NY City underwater with the Statue of Liberty half submerged.
There are two important points which readers must be aware of from the first mention of SLR:
- SLR is a real imminent threat to coastal cities and low-lying coastal and near-coastal densely-populated areas.
- SLR is not a threat to anything else — not now, not in a hundred years — probably not in a thousand years — maybe, not ever.
It is easy enough to find some place on the planet foolishly built and occupied within a few feet of local relative sea level at some time in the past which is now flooding at Spring Tides [sometimes referred to as King Tides] or during periods of storm surge. Given that the average rise of the seas over the last century or so (the total length of our dependable instrumental record) has been about 8 to 12 inches, the chance that occasional tidal flooding will occur in these locations is almost 100%.
SLR is a real threat to coastal cities — today
First, let’s not kid around — The sea itself, whether rising or not, is a real imminent threat — a clear and present danger — to the many coastal cities and highly populated areas of the world that lie at or very near local mean sea level.
My recent essays on Miami Beach and Guangzhou–Canton point up real-life present-time examples of entire cities at risk from today’s sea level, today’s tides, and already experienced storm surges. Streets and neighborhoods have been built below Mean High High Water (highest normal tides) and below-ground infrastructure (water and sewage pipes, underground utilities, parking garages, subways) built many feet below sea level requiring them to have pumps to keep things dry and working.
There are not only cities currently below sea level (New Orleans, Amsterdam, Georgetown [Guyana]) but also major portions of whole nations (the European Low Countries and parts of the UK and Ireland among them). In Asia, Bangladesh, most of which is made up of river delta less than 12 m/40 ft above sea level, about 10% of its land would be flooded by 1 m/3 ft of SLR or storm surge.
Any sea-side or estuary-side city with major assets within ten feet of current sea levels are at risk now and those not taking active measures to mitigate those risks are placing losing bets on their futures. The tendency of societies to allow building in harm’s way seems inexhaustible — and to me, inexplicable.
The megapolis of Los Angeles, California is one of the country’s largest cities (and place of my birth, these many long years ago). It is nestled in the Los Angeles Basin, surrounded by coastal mountains.
An inundation of greater Los Angeles would be a truly world-class disaster. It is home to over 18 million people.
The NOAA Sea Level Rise Viewer, designed to inform us of the threat of sea level rise, allows us to map the inundation that would be caused by up to 6 feet (2 meters) of sea level rise. Let’s see what that would look like if it happened to LA — here is Los Angeles Basin, with six feet of extra sea level:
Now look at that — almost nothing happens. From Santa Monica in the north all the way down to San Pedro, almost exactly nothing. Up near the top , there is the bright green “low-lying area”. Primarily a section called Venice (you guessed it — a developer built canals lined with houses – waterfront homes) and a little flooding near the Marina Del Rey and Playa Del Rey (the King’s Beach in English). Marinas are built more-or-less at sea level by necessity — Marina Del Rey in the mouth of a river estuary and a small slough or brackish wetland. Then absolutely nothing until one rounds the Palos Verdes peninsula (Green Hills) and comes to San Pedro, the seaport of Los Angeles.
Let’s enlarge that portion of the map:
Pushing the sea level rise viewer slider all the way up to 6 feet gives us some flooding in the sea port — here there are the docks and warehouses, built intentionally just a few feet above MHHW (mean high high water) so that vessels can be unloaded conveniently. Circled in RED is an area of light industrial buildings associated with the docks and shipping industry, located along a sea-level river. The newer Long Beach Harbor area is unscathed.
There is bad news further south-east. Circled in YELLOW are areas of single-family homes built on what were salt marshes and a sandy, brush-covered sand bar, outfitted with canals so more homes could have their own docks on the water. Leisure World, a huge mobile and manufactured home park, also built in a filled salt marsh is entirely flooded out at six feet. Sunset Beach is a Miami-like development of canals and water-front homes built just above mean high high water.
The Naval Weapons Storage facility, built at sea level to accommodate loading munitions onto naval vessels, gets flooded, but not the storage areas themselves. The flood-prone portions make up an associated, not always open-to-the-public, nature preserve. Close-up views show the munitions storage bunkers built on raised-out-of-harms-way leaf-like islands, far from civilian populations.
The area circled in ORANGE is shown as already flooding at King Tides. Let me add that image once more, to keep it in view:
Right on the coast in this section is a State Marine Conservation area, but inland in deep water (at six feet of SLR) are literally thousands of single-family homes, cheek-to-jowl.
Just to the south, one half of Huntington Beach is flooded out. The area now covered with homes was in the 1920s and 1930s part of the great California Oil Boom, and looked like this:
By the 1950’s, the oil boom had moved on, and the low-lying lands were cleared for home-building to accommodate the post-war families cranking out the baby boom. As we can see from the flood map, little attention was paid to elevation or concerns about the sea. Riverbeds connect to the sea and bring the rising tides inland where the land is not protected by bluffs — one can see the bluff in the right hand side of the photo above….but further north (left hand side) the bluff doesn’t exist).
What has happened here?
Let’s try to be very clear about what has been allowed to happen here. Humans have been able to measure relative elevation for at least 150 years, since about 1850 when spirit leveling first came into use.
This means that when land is developed near a body of water, like the Pacific Ocean or its connected estuaries, it can be assumed that it was possible to know the differences between the elevation of the water (sea level) and the elevation of the land. Any time that modern infrastructure — buildings, homes, factories, warehouses — was built, the builders knew (or certainly were obligated to know) the elevation of the land above sea level.
Sea level, worldwide, is understood to have generally risen 8 to 12 inches over the last century. So all of the areas shown as flooding at six feet of SLR have been built on and developed despite their being 5 feet or less above expected levels of the sea on the day construction was started.
Terminal Island (in Long Beach, the port of Los Angeles) has a tidal range of 5.5 feet (1.7 meters), with Mean High High Water being about 2 ½ feet higher than mean sea level. The NOAA Sea Level Viewer adds “sea level rise” to Mean High High Water — which can be considered the same as Spring or King Tide.
Mean High High Water is not to be confused with the tidal datum known as “Maximum — Highest Observed Water Level”. The tide station at Los Angeles, located in San Pedro Bay, has an historical Maximum that is another two and a half feet higher than MHHW, meaning that many of these flooded areas have already been flooded at existing sea levels.
The Bottom Line for Los Angeles:
Most of the megapolis of Los Angeles is protected from any threat from the sea by the bluffs along its coastline, with some minor exceptions at river estuaries, where some incursion could take place if there was to be six feet/two meters of sea level rise.
Where the greed of developers and lack of foresight by city planners (under the assumption that there was anyone doing city planning) has allowed thousands upon thousands of homes to be built in harm’s way in Sunset Beach, Huntington Beach, Seal Beach and other low-lying beach communities at the southern edges of the LA Basin. These homes stand at risk under present sea levels, requiring only King Tides and Storm Surges to inundate them with as little as six feet of extra sea level. As a comparison, Los Angeles has already historically experienced high water half of that in the past. As a reminder, Hurricane/Tropical Storm Sandy recently pushed 13 feet of storm surge into New York Harbor.
How much SLR can we expect?
What can we expect from rising seas? The generally accepted guess is “more of the same” — about 1 foot per century. If the temperatures rise a bit more, as expected by the luke-warmers in Climate Science, this could increase to about 18 inches over the next 100 years.
Los Angeles, though founded in 1781, did not become a mega-metropolis until after the 1920s, about a hundred years ago and may have seen the one foot of SLR over the last 100 years but it will not see 6 feet of SLR in the next few hundred years, so they have plenty of time to adapt and prepare.
The situation in LA’s low-lying, at-risk areas will not get much worse due to actual rising seas within a reasonable time scale. But, with the understanding that some areas are already at risk at current levels, anything other than a sea level drop will make a bad situation worse in those areas.
Neighborhoods built on sea-level canals with only a foot or two of freeboard (the factor of safety, usually expressed in feet above a sea level or MHHW) will probably have to be abandoned over the long term. Building codes will need to be enacted forbidding building on low lying areas prone to sea water inundation. All new homes built in flood-prone areas should be mandated by code to be built on “stilts” or with living spaces raised on eight to ten foot foundations as they are now in some East Coast areas. Existing homes in many areas will have to be raised or when next flooded, abandoned.
Southern Florida has been making these types of changes in building codes and development requirements for the last ten years, along these lines, requiring new homes to be at least a foot above FEMA flood map levels. Sea walls, when newly built or repaired are required to be raised to match expected flood levels. New homes in the Beaufort area of North Carolina (and all throughout the low country as it is called) can be seen going up in compliance with codes requiring living areas to be raised — most often ground level is dedicated to garage and storage space, and the living spaces up one floor. The following image shows (in light blue) how much land would be flooded by 6 feet of SLR or storm surge.
As a personal note, my wife and I sat out Hurricane Irene in August 2011, near Beaufort, NC, in a tiny marina along the Atlantic Intracoastal Waterway, about three miles inland. There we had over 8 feet of storm surge. We watched as the docks and the pilings disappeared under the rising waters. We had our car parked on a hill 10 feet above MSL, it was touch and go through the night whether the hill too would be flooded. (On the map above, Beaufort is just south of the “ville” portion of the city name for Jacksonville.)
The Low Countries of Europe have long ago developed the engineering skills necessary to deal with and mitigate past errors of building too close to sea level. The rest of the world’s nations and cities each need to carry out an exercise similar to the one above — and as was done in Dade County — much more detailed and exacting on the level of professional civil engineering and develop mitigation plans for their current situation and for the expected continued rise in sea levels over next century — mitigation plans that will correct for past errors and oversights and protect them in both the short term and the long term.
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- local relative sea level — the average level of the surface of the sea in relation to the land at any given locality. NOAA says : Tide stations measure Local Sea Level, which refers to the height of the water as measured along the coast relative to a specific point on land. Water level measurements at tide stations are referenced to stable vertical points (or bench marks) on the land and a known relationship is established.” (back to essay)
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Author’s Comment Policy:
I am always eager to read your comments and to try and answer your on-topic questions.
Try not to jump ahead of the series in comments — this essay covers only the existing sea level threat with a single example (added to the examples in my previous sea level essays). I will cover, in future parts of the series: How is sea level measured? Do we know that sea level is really rising? How fast is it rising? Is it accelerating? How do we know? How accurate are sea level measurements anyway? Should I sell my sea front property?
Sea Level Rise is an ongoing Scientific Controversy. This means that great care must be taken in reading and interpreting new studies and especially media coverage of the topic (including this essay) — bias and advocacy are rampant, opposing forces are firing repeated salvos at one another in the journals and in the press and the consensus may well simply be an accurate measure of the prevailing bias in the field. (h/t John Ioannidis)
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