Guest Essay by Kip Hansen
The New York Times has treated its readers to an in-depth piece in the Science section with the provocative title: ‘We Cannot Save Everything’: A Historic Neighborhood Confronts Rising Seas. In the article, by author Cornelia Dean, the claim is made that:
“Climate change is forcing experts to reimagine the future of historic preservation here.”
“Rising seas have left preservationists wondering how, or even whether, to save some Colonial-era homes here”.
“The Point, [ in Newport, R.I.] a waterfront neighborhood here, is one of the largest, best preserved and most important Colonial-era communities in the United States. Its grid of 18th-century streets contains scores of houses built before the American Revolution, and dozens more that are almost as old.”
“Today, the neighborhood faces a new threat. The Point sits only a few feet above sea level, and because of climate change, the ocean is rising. So people have been thinking again about how to preserve the neighborhood.”
SPOILER: Is Historic Newport, RI Threatened by Sea Level Rise?
YES and NO
Yes, the neighborhood called The Point is at risk from normal everyday, centuries-long absolute sea level rise which accounts for much of the relative sea level rise at Newport exacerbated by the subsidence of the low-lying neighborhood as the now centuries-old fill continues to settle and to wash out from under it with each tide cycle as it has from the moment the fill was dumped into the harbor to create the land the neighborhood was built on.
For those still interested, it is a useful mental exercise to go through the steps necessary to arrive at the above conclusions.
So, let me set some of things straight concerning the claim:
a. “because of climate change, the ocean is rising.” — Sea level, worldwide, is rising and according to NOAA, “the absolute global sea level rise is believed to be 1.7 +/- 0.3 millimeters/year during the 20th century.” 2 mm a year for 100 years = 200 mm = 7.8 inches. This long-term rate of global sea level rise is generally quoted to be 8 to 12 inches pre century — depending on the source. The linear trend of absolute sea level rise (how much higher the sea surface is from the center of the Earth) is literally a straight line:
Note that NOAA makes two different statements about sea level rise: one based on long-term historic data (as above) — “absolute global sea level rise is believed to be 1.7 +/- 0.3 millimeters/year during the 20th century” and produces another, the graph here, of satellite measured SLR, which they state is “2.9 ± 0.4mm/year” in the satellite era. There has, as yet, been no real definitive reconciliation between the two figures in the literature. The long-term difference between the two, over a century, would be about 4 inches. The satellite’s additional four inches do not appear at GPS-corrected tide gauges around the world. The most cited reference for this is Church and White (2011) [ .pdf here ].
Our rule-of-thumb guess-timate of “8 to 12 inches” per century covers both the tide gauge and satellite calculations. There is some increase in volume of sea water as it warms, but it has not recently or radically warmed differently than since the end of the Little Ice Age, circa 1800-1850 or so.
The change in the climate from the Little Ice Age to the Modern Warm Period has caused, and is causing, the seas to rise at a more-or-less steady rate, for 170 years now, of about 1.5 to 3mm per year or between 5/100th to 1/10th of an inch each year.
b. “Climate change is forcing experts to reimagine the future of historic preservation here.” Above, we cover the “climate change” claim — it is the change from the Little Ice Age to the Modern Warm period that is the change responsible — “here” is generally Newport, Rhode Island. Let’s check the tide gauge data there:
In the last 100 years, relative sea level, at the tide gauge, has risen about 9 inches (we’ll give it the standard 8-12 if you wish). NOAA’s note at the bottom of the image gives 9.1 inches. Remember that the tide gauge has been changed (and probably moved) several times since 1930, and it currently looks like this:
The tall white tubes on this side of the gangway are the measuring device itself, and the electronics (computers, satellite dish, etc.) are in the white waterproof steel box on the quay. Notice that the quay is obviously constructed on fill — it not only isn’t a natural part of the land, it has been created by dumping rocks and soil into the water at the edge of the harbor, and reinforced with large blocks of concrete. There is no way of easily determining whether or by how much the quay is settling (subsiding), thus the tide gauge, as NOAA points out, measures only Relative Sea Level and the rate of change represents 1.7mm/year plus or minus vertical land movement — in this case almost certainly subsidence.
Newport, Rhode Island does have a Continuously Operating GPS Reference Station (CORS) but it is not here at the tide gauge. It is up on the hill, attached to bedrock:
What does that means for us? The CORS data shows that Coasters Harbor Island, home to the US Naval War College among other things, has recently (short-term) been subsiding at a rate of about 2.6mm/year. [Important Note: the short term GPS solution for any CORS station may be different than the long-term solution.] There is a long-term solution for Vertical Land Movement (VLM) from 2006 in Snay et al. (2007) which gives the VLM as -0.01 ± 1.16/mm year, basically, zero. This aligns with the know phenomena of geostatic hinging of the Eastern U.S. Seaboard just north of Boston, MA, with land to the north rising and land to the south subsiding as a result of the melting miles-thick ice of the last glacial period. With Rhode Island being just below the hinge-point, it would not be expected to be subsiding by very much.
In 2013, NOAA provided a new estimate of Relative SLR at Newport Tide Gauge of 2.58 ± 0.19/mm/yr and a VLM Trend (as derived from tide gauge data) of -0.88 ± 0.09/mm/yr. Notice that 2.58 mm minus 0.88 mm (negative VLM) equals exactly (by chance?) NOAA’s long-term figure for global absolute sea level rise of 1.7 mm/yr.
Recall, that global sea level is said to be rising at somewhere from 1.5-3.0mm year — the current subsidence of the bedrock (on a scale of months) at Newport is of an equal magnitude. So, we should see substantial change in Relative SLR at the tide gauge — it should be about Local Subsidence + Global SLR.
The short-term subsidence doesn’t appear much in the tide gauge record — but it is very small, low single digit millimeters. Regardless, the tide gauge is attached to a concrete pier obviously build on fill used to create the yacht harbor we see in the satellite view, and therefore can be reasonably assumed to be subsiding at some unknown rate greater than that of the larger island, the tide gauge data shows a steady rate of Relative Sea Level Rise of 2.77mm/year — which is 0.1mm more than the measured short-term subsidence Coasters Harbor Island and in line with NOAAs most recent (2013) long-term solution for RSLR and VLM at the Newport Tide Gauge.
So to summarize, for Newport, R.I., in general, based on the tide gauge and CORS data, Relative Sea Level RISE there is running about 10 inches a century — if this has been true and steady since colonial times, we are looking at two centuries times 10 inches gives 20 inches or 0.5 meters.
It’s Worse than We Think @ The Point;:
“The Point was settled in the 17th century by Quaker refugees from Massachusetts. Then, it was little more than a spit of land sticking out into what became Newport Harbor. Soon, as its edges were filled in, a marsh became Marsh Street, and a wet area became Water Street; the path of a span that once linked The Point to the rest of Newport turned into Bridge Street.”
The Point is one of the neighborhoods that has an association and a set of by-laws (link is a .docx). The by-laws lay out the boundaries which I have drawn (approximately) on this map:
I’ve drawn a line pointing to Marsh Street, which runs almost the entire width of The Point. And marked a pointer to Bridge Street. My point? The Point used to be a little spit of and protruding into Newport Harbor — but even in colonial days they began to fill in the edges creating a vast area of new land on which colonial homes were built. That filled area became known as The Point. There is no longer a land feature that looks like a “point”,” narrow piece of land which sticks out into the sea” — as one can see on the map — it is just one big flat, nearly sea-level neighborhood extending south from what is now Highway 138 down to just south of the site of the Newport Marriot Hotel, and by fiat includes Goat Island.
Being a bit leery of using NY Times bespoke photos without permission, I offer this link (opens in a new tab or window) showing why The Point has a problem — it has the same vice that much of Miami Beach has — “Miami’s vice is water, as in waterfront. Everybody seems to want a house on the waterfront…”. This was apparently true in colonial times as well — a whole neighborhood was built by filling a marsh and extending the land into the harbor to create more waterfront with better views for those desiring “Elaborately detailed homes [that] reveal the fortunes of those who lived there centuries ago, reeling from the incredible profits made as sea traders and an important piece of the trans-Atlantic slave trade for many years.” [ source ]. As the Times was careful to explain “The Point sits only a few feet above sea level”.
Built on land fill, in the days before modern harbor engineering, The Point has been subjected tidal washing of the filled areas — here’s the data in one image:
Tidal wash has been affecting The Point for 200 years….during which time Mean Relative Sea Level had probably risen about 20 inches. Highest Recorded Tide Level at Newport was 13.31 feet (above MLLW) or ten feet above todays Mean High Water recorded on September 21, 1938.
For The Point, flooded basements and flooded first floors are not a new phenomenon, where the most of the historic houses are just a few feet above sea level. Note that the basement floor of a home 3 feet above sea level will be below the high tide level by 5 feet or so. If its foundation is permeable (not watertight like a swimming pool) it will need constant pumping to keep it dry. And they do.
And the rest of the story?
The rest of the NY Times’ piece is an interesting discussion of technical solutions for historic buildings that are endangered by the combination of slowly rising seas and slowly sinking neighborhoods.
# # # # #
Author’s Comment Policy:
This is probably my last piece on places supposedly “threatened by climate- change-caused sea level rise”. They are boring because, when investigated closely, the problem and its cause do not change: the absolute sea level of our oceans is rising, ever so slowly, it has been and will continue to do so until we arrive at the next cooling period. All of the places claimed to be threatened by climate change driven SLR, which I have investigated so far, are in fact subsiding (sinking towards the center of the earth) ever so slowly or, in some cases like Jakarta, quite rapidly. None have exceptional (differing hugely from worldwide absolute SLR) actual rising sea levels (only rising Relative Sea Level).
I tried to save readers some time by giving a spoiler at the beginning for those in a hurry. Any readers in Rhode Island should let us know their situation if they live on the waterfront somewhere.
Thanks for reading.
# # # # #
via Watts Up With That?
July 15, 2019 at 12:53PM