Sea level rise acceleration (or not): Part VII U.S. coastal impacts

by Judith Curry

The final installment in the CE series on sea level rise.

1. Introduction

Global mean sea level (GMSL) has increased by about 8–9 inches since 1880, with about 3 inches occurring since 1993. As discussed in Part VI, scientists expect that GMSL will continue to rise well beyond the 21st century because of global warming that has already occurred and warming that is yet to occur.

The recent NOAA Report Global and Regional Sea Level Rise Scenarios for the United States has stated that even the relatively small increases in sea level over the last several decades have been associated greater storm impacts at many places along the U.S. coast. Further, the frequency of intermittent flooding associated with unusually high tides has increased rapidly in response to increases in local sea level, becoming a recurrent and disruptive problem.

Millions of people in the U.S. already live in areas at risk of coastal flooding, with more moving to the coasts every year. Rising seas will dramatically increase the vulnerability of this growing population, along with critical infrastructure related to transportation, energy, trade, military readiness, and coastal ecosystems and the supporting services they provide. It has been estimated in the NOAA report that 35 inches of sea level rise would permanently inundate areas currently home to 2 million Americans.

This essay addresses the U.S. coastal impacts of sea level rise. Apart from the issue of the extent to which global mean sea level rise can be attributed to human caused warming, this essay provides regional and local contexts for sea level rise against the broader context of global sea level rise. The analysis includes a focus on:

  • Mississippi delta region
  • Barrier islands
  • Cities: San Francisco, New York, Miami

2. Perspective from the IPCC AR5

An overview of the impacts of global sea level rise on coastal regions is provided by the IPCC AR5 WGII Chapters 5 and 18. Chapter 18 includes an assessment of the challenges of attributing any of these impacts to human-caused global warming. Excerpts:

While it is likely that extreme sea levels have increased globally since the 1970s, mainly as a result of mean sea level rise due in part to anthropogenic warming, local sea level trends are also influenced by factors such as regional variability in ocean and atmospheric circulation, subsidence, isostatic adjustment, coastal erosion, and coastal modification. As a consequence, the detection of the impact of climate change in observed changes in relative sea level remains challenging. [AR5 WG II 18.3.3]

Anthropogenic causes of RSLR (regional sea level rise) include sediment consolidation from building loads, reduced sediment delivery to the coast, and extraction of subsurface resources such as gas, petroleum, and groundwater. Subsidence rates may also be sensitive to the rates of oil and gas removal. [T]he majority of the world’s largest deltas are currently subsiding at rates that are considerably larger than the current rates of sea level rise because of coastal sediment starvation due to substantial dam building over the 20th century or sediment compaction through natural or anthropogenic activities. Many large cities on deltas and coastal plains have subsided during the last 100 years: ~4.4 m in eastern Tokyo, ~3 m in the Po delta, ~2.6 m in Shanghai, and ~1.6 m in Bangkok. Loads from massive buildings and other large structures can also increase sediment compaction and subsidence. Regional sea level rise can exceed global mean sea level rise by an order of magnitude reaching more than 10 cm/yr. [AR5 WG II]

[T]here are multiple drivers involved in shoreline erosion that are unrelated to climate change including long shore sediment transport; the diversion of sediments by dams; and subsidence due to resource extraction, mining, and coastal engineering and development. Owing to the multiple natural and anthropogenic stressors contributing to coastal erosion, confidence in detection of a climate change contribution to observed shoreline changes is very low, with the exception of polar regions. [AR5 WG II 18.3.3]

Aquifers on the coasts of the USA have experienced increased levels of salinity largely due to excessive water extraction. Natural drivers combined with over-extraction, pollution, mining, and erosion compound groundwater supply problems. [AR5 WG II] Attribution of saline intrusion to incremental sea level rise is still not sufficiently supported. [AR5 WG II]

Coastal lagoons and estuaries, as well as deltas, are highly susceptible to alterations of sediment input and accumulation, processes that can be influenced by climate change via changes in mean and extreme sea levels, storminess, and precipitation. However, the primary drivers of widespread observed changes in those systems are human drivers other than climate change so that there is very low confidence in the detection of impacts related to climate change (Section 5.4.2). [AR5 WG II 18.3.3]

Summary. There is no question that local sea levels are increasing in some locations at rates that are causing damage in coastal regions. However attributing these changes to human caused global warming (even if you assume that recent global sea level rise is caused entirely by greenhouse gas emissions) is very challenging. This is because there are much larger impacts on local sea level rise from local geological processes, land use practices and coastal engineering.

3. Causes of regional sea level change

Sea levels have not been rising uniformly across the globe over the last century. The causes of regional sea level rise are summarized in the 2017 NOAA Report on Global and Regional Sea Level Rise Scenarios for the United States.

One reason for regional variations in rates of sea level rise is dynamic redistribution of ocean mass via ocean circulations. There are two regional patterns that impact U.S. coastlines. The Pacific Decadal Oscillation (PDO) has resulted in recent trends in the western Pacific that are much higher than the global rate (>10 mm/yr) to less than 1 mm/yr at several regions on the U.S. west coast. 
Along the Northeast Atlantic coast, sea level trends have been higher than the global rate in recent decades. The relatively high rates have been attributed to changes in the Gulf Stream.

Vertical Land Motion (VLM) can be a significant factor in the overall rate of local/regional sea level rise (RSL) trends. The highest RSL rise trends are found in regions of Louisiana (8–10 mm/year), Texas (4–7 mm/year) and along the Northeast Atlantic from Virginia to New Jersey (3–5 mm/year) (NOAA). In these regions, glacial isostatic adjustment (GIA) and sediment compaction add about 0.5–2 mm/year to RSL change, and groundwater and oil/gas extraction processes further enhance RSL rise. Land subsidence rates of 2–5 mm/year or more are not uncommon for regions of the Northeast Atlantic and Gulf Coasts.
Glacial Isostatic Adjustment (GIA) is the ongoing response of the solid Earth to land-ice shrinkage since the end of the last ice age. Melting glaciers and ice sheets and changes in land-water storage not only change ocean mass and thus GMSL, but also produce regionally distinct signatures from changes in the Earth’s gravitational field and rotation, and lead to regional VLM.

The NOAA Report projects the following patterns of U.S. regional sea level (RSL) rise:

  • Future (Regional Sea Level) RSL rise is amplified along the Northeast U.S. coast due to the effects of GIA, the far-field static equilibrium effects of Antarctic melt, and reduced transport of the Gulf Stream. Future RSL rise is partially reduced by intermediate-field static-equilibrium effects associated with relative proximity to Greenland and many northern glaciers.
  • RSL rise is amplified along the western region of the Gulf of Mexico and much of the Northeast Atlantic coast by withdrawal of groundwater and/or fossil fuels.
  • Future RSL is reduced along the Alaska and the U.S. Pacific Northwest coasts due to proximity to the Alaskan glaciers from both ongoing GIA to past glacier shrinkage and projected future losses.
  • Under the higher future SLR scenarios, RSL is amplified along the continental U.S. Pacific Coast due to far-field static-equilibrium effects of Antarctic ice sheet melt.

The 2018 NOAA Report on Patterns and Projections of High Tide Flooding Along the U.S. Coastline addresses the issues surrounding high tide flooding. High tide flooding affects low-lying assets and infrastructure such as roads, harbors, beaches, private and commercial property, and public storm-, waste- and fresh-water systems.

High tide flooding occurs more often in certain seasons and during certain years. During an El Niño, high tide flood frequencies are amplified at about half of the U.S. coastal locations. Over the last several decades, annual frequencies of high tide flooding have been increasing along the Atlantic and Gulf coasts.
Projections from the NOAA Report find that by 2100, high tide flooding will occur ‘every other day’ (182 days/year) or more for

the Intermediate Low Scenario within the Northeast and Southeast Atlantic, the Eastern and Western Gulf. The Report concludes that the U.S. coastal cities are close to a tipping point with respect to flood frequency, as only 0.3 m to 0.7 m separates infrequent damaging-to-destructive flooding from a regime of high tide flooding—or minor floods from moderate and major floods.

4. Sea level rise ‘hot spots’

A recent article in the Conversation explains the issue: X-factor in coastal flooding: natural climate patterns create ‘hot spots’ of rapid sea level rise. The article is written by authors of the  recent publication Spatial and temporal variability of sea level rise hot spots over the eastern United States. Excerpts from the article:

[We] found that sea level rise had accelerated rapidly at nearby Trident Pier [Florida] between 2011 and 2015. While global sea level has been rising at an average pace of about 1 foot per century, this site had recorded an increase of about 5 inches in a mere five years.

These rates were ten times higher than the long-term rates of sea level rise along the Florida coastline. Further investigation showed that all tide gauges south of Cape Hatteras showed a similar uptick over the same period. Such hot spots have occurred at other points along the Eastern Seaboard over the past century. Now we see indications that one is developing in Texas and Louisiana.

A recent paper by McCarthy et al. proposed that the North Atlantic Oscillation (NAO), a seesaw pattern in air pressure over different regions of the North Atlantic Ocean, could explain the shift in the position of short-term variations in sea level rise. Shifts in the NAO alter the position of the jet stream, wind patterns and storm tracks, all of which affect the distribution of water in the North Atlantic basin. Ultimately, the cumulative effects of NAO on the ocean determine whether water will pile up to the north or south of Cape Hatteras. Thus, water piled up preferentially to the north of Cape Hatteras in the period 2009-2010, and to the south from 2011 to 2015.

This NAO-related mechanism explained where sea level accelerations might occur along the Atlantic coast, but did not seem to explain their timing. We [found] that the timing of short-term sea level accelerations, lasting one to several years, was correlated with ENSO.

Although ENSO occurs in the Pacific, its effects propagate across North America, altering air temperatures and wind regimes in the eastern United States. These changes in wind distributions can affect water transport in the North Atlantic Ocean, causing it to build up along the U.S. Eastern Seaboard at times.

We found that short-term accelerations in sea level rise have repeatedly occurred over the last century, sometimes occurring south of Cape Hatteras and sometimes focused north of the Cape. These hot spots can exceed rates of 4 inches in five years, and can occur anywhere along the U.S. Atlantic coast. They form when the accumulated signals of ENSO and the NAO converge, displacing seawater toward the coastline.

5. Barrier islands and deltas

The most vulnerable regions to sea level rise are the barrier islands along the U.S. coast and the Mississippi Delta.

5.1 Mississippi delta

As per the Wikipedia :

The Mississippi River Delta region is a 3-million-acre (12,000 km2) area of land that is part of the Louisiana coastal plain, one of the largest areas of coastal wetlands in the United States.The Mississippi River Delta containing more than 4000 square miles of coastal wetlands and 37% of the estuarine marsh in the conterminous U.S. The coastal area is the nation’s largest drainage basin and drains about 41% of the contiguous United States into the Gulf of Mexico.

A new paper by Chamberlain et al. (2018)  provides an anatomy of the dynamics of the Mississippi delta. Deltas can undergo rapid transformations due to reductions in sediment supply, accelerating rates of sea-level rise, plus high subsidence rates. The Mississippi delta is undergoing all three processes. Preindustrial conditions produced 6 to 8 km of new land per year. However, these rates are several times lower than rates of land loss over the past century. Recent land loss rates (~45 km2/year) in combination with the global sea-level rise acceleration, net land loss in the Mississippi delta will likely continue regardless of coastal restoration strategies.

A recent paper by Maloney et al (2018) finds that the Mississipi River delta is entering a period of retrogradation owing to the decline in the incoming sediment. Since the 1950s, the suspended sediment load of the Mississippi River has decreased by ~50% due primarily to the construction of >50,000 dams in the Mississippi basin. They found that the Mississippi River delta front has entered a phase of retrogradation, which occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is less than the volume of the delta that is lost through subsidence, sea level rise and/or erosion.

A new subsidence map of coastal Louisiana developed by researchers at Tulane University finds the region to be sinking at just over one third of an inch per year (or 9 mm/yr) [compare this value with the average rate of global sea level rise of 3 mm/yr].  The average elevation of New Orleans is currently between 1-2 feet below sea level, with elevations ranging from 20 feet above sea level to 7 feet below sea level.

It may seem that fighting to save the Mississippi delta region is a losing battle. However a recent WaPo article describes how the Louisiana Coastal Protection and Restoration Authority, using funds from the British Petroleum oil spill settlement, is moving forward with two large sediment “diversions.” These diversions will start channeling huge volumes of river water in new directions, in a bid to protect areas around New Orleans in particular.

Summary. The issue of sea level rise and land loss in the Mississippi delta region is complex, with geological subsidence and the decline in sediment transported by the Mississippi river being the dominant drivers. For a city whose elevation averages one to two feet below sea level, sea level rise from human caused warming does not seem to be the dominant driver for the problems that the region is facing.

5.2 Barrier islands

Barrier islands are a type of dune system that form by wave and tidal action parallel to the mainland coast. They are subject to change particularly during storms, but protect the coastlines from storms and create areas of protected waters for wetlands. The morphology of barrier islands is determined by tides, wave energy, sediment supply, sea level trends and the seabed morphology. The amount of vegetation on the barrier island has a large impact on the height and evolution of the island. Barrier islands are prominent on the U.S. East Coast and Gulf Coast; no barrier islands are found on the U.S. Pacific coast due to the rocky shore and short continental shelf.

The barrier islands are beautiful and provide homes to many important ecosystems. Some of the islands have undergone a great deal of development for tourism and residential communities.

Louisiana has 8 barrier islands. Much ado has been made about the ‘climate refugees’ from Isle de Jean Charles, which is disappearing – in 1955, there were 22,000 acres while there are 320 acres today [link]. The principal problem traces back to the Great Mississippi Flood of 1927 when the corps of engineers responded by building giant levees to constrain the river, which stopped the flow of sediment into its delta. It appears that these refugees should more accurately be referred to as ‘Mississippi flood mitigation refugees.’

The Wikipedia lists 45 barrier islands in Florida, which make up more than 700 miles of Florida’s coastline. The Florida barrier islands have gorgeous white sand beaches and are popular tourist destinations. Many have vibrant, wealthy residential communities.

Studies are underway to develop proposals to raise roads on Key Largo and Miami Beach [link]. Drainage solutions common in other areas won’t work on the Florida Keys, since there is porous limestone rock underneath the soil. When water levels get high, porous rock is filled with groundwater and can crack asphalt. High groundwater also means pumps are needed to send the water elsewhere, as Miami Beach does. Miami Beach has become a laboratory for sea level rise mitigation efforts. However, residents in Miami Beach are pushing back against plans to raise streets, since the fear this will bring flooding into homes.[link]

There is also concern about Georgia’s barrier islands. Georgia’s costal islands are constantly changing from the natural directions of the currents. If these barrier islands continue to erode with rising sea levels, Georgia’s mainland coast will become more susceptible to erosion and to powerful coastal storms. But it’s not all bad news. Irma’s winds carved a new island off the Georgia coast [link]. The 100-acre island broke away from Blackbeard Island, which is near Sapelo, about 60 miles south of Savannah. This piece of land had been slowly separating from Blackbeard Island for decades, and was barely connected before the hurricane.

Summary. The morphology of barrier islands is very dynamic. Storms and engineering practices that influence the natural flow of sediment have a substantial influence on this morphology, independent of sea level rise (of course, sea level rise is not helping). Particularly for the barrier islands that have developed wealthy communities, aggressive engineering strategies are being developed. These most vulnerable islands are becoming laboratories for coastal sea level rise adaptation strategies. But it is probably futile to expect these changeable islands to remain as geologically stable entities for a very long times.

6. Coastal cities

Nearly all of the cities along the U.S. coast are concerned about sea level rise. This section focuses on two of the largest coastal cities facing sea level rise problems:

  • Miami
  • New York City
  • San Francisco

6.1 Miami and south Florida

Miami has a population of more than 5.5 million living at an elevation of 6 feet above sea level.

The impact of the ‘hot spot’ on Miami is described in an article at gizmodo. Around 2011, the slow upward creep of the ocean seemed to kick into high gear, with tidal gauges recording much faster rates of sea level rise and residents noting a stark uptick in so-called “nuisance” floods. A new study confirms that this was not Floridians’ imaginations: From 2011 to at least 2015, the rate of sea level rise across the southeastern US shot up by a factor of six, from 3-4 millimeters a year to 20.

From a recent BBC article about Miami’s sea level rise:

For both Fort Lauderdale and other communities across south Florida, the main problem is drainage. The systems here were designed to let stormwater drain into the ocean when it rains. Because homes and gardens are higher than the crown of the road, the streets flood first in a storm, by design. Water runs into the storm drain and is piped into the ocean or waterways that lead there. At least, that’s what is supposed to happen. With sea levels now often higher than the exits to the run-off pipes, saltwater is instead running up through the system and into the streets. To make matters worse, when the sea gets even higher, it can breach the seawall, flood people’s yards and flow down to the road – where it stays.

Nobody’s doing better adaptation work in the country than south Florida,” says Daniel Kreeger, executive director of the nonprofit Association of Climate Change Officers. But the question isn’t whether this work will save every community: it won’t. Even those tasked with making their cities resilient admit that, at some point in the future, certain areas here will no longer be “viable” places to live. Rather, the challenge is to do enough to ensure that the economy as a whole continues to thrive and that tourists still come to enjoy the sun, sand – and swelling sea.

Well, what is the near-term bottom line for Miami regarding sea level rise?  A recent NPR article sums it up: South Florida Real Estate Boom Not Dampened by Sea Level Rise.

6.2 New York City

In New York City, sea level has risen 11 inches over the past century, which is a greater rate than mean global sea level rise. It has been estimated [link]
that land subsidence [sinking] in the New York City area has been roughly 3-4 inches per century.

New York City is particularly vulnerable to the effects of sea level rise because it is built primarily on islands and has 520 miles of coastline [link]. The City’s waterfront is among its greatest assets. Wealthy New Yorkers have a predilection for living along the waterfront in Manhattan, Brooklyn and Queens. There is also substantial infrastructure and municipal facilities along the coast, including roads, bridges, parks, waste transfer stations and wastewater treatment plants, that are at risk from sea level rise.

New York City has been proactive in tackling climate change risks and sea level rise, even before Hurricane Sandy in 2012 [link].  Following Hurricane Sandy, a comprehensive plan has been developed: City of New York: Building a Stronger, More Resilient New York.

6.3 San Francisco

Sea level has been measured in the San Francisco Bay area since the 19th century. Over the past the past 100 years, sea level has risen by 7.7 inches, which is slightly lower then the global average rate.

The Bay area’s problem with sea level rise is summed up by the title of this article: Rising Seas are Quickly Sinking Bay Area Landfill Zones,
which is based on a publication by Mirzaei and Burgmann. From the article:

Landfill zones are sinking due to soil compaction, and at a rather alarming rate. “We found that they’re sinking as much as one-half inch (12.7 millimeters) annually,” says Bürgmann. “Sea level rise, by contrast, is on the order of one to three millimeters per year.” The new maps identify 48 to 166 square miles as prone to inundation. Half of San Francisco International Airport’s runways could be underwater by the turn of the century.

Landfill compaction isn’t the only cause of land subsidence in the Bay Area. River and stream outflows into the bay deposit a lot of silt and mud and these areas also are subsiding as they become compacted and dry out. Another major contributor to land subsidence is groundwater pumping.

7. Reconciling historical and future projected sea level rise accelerations

Watson (2016) published an analysis of the sea level rise data for the U.S., using Singular Spectrum Analysis (SSA). The analytical package used by Watson is designed to enhance estimates of trend, real-time velocity and acceleration in the relative mean sea-level signal derived from long annual average ocean-water-level time series. Key findings from the study:

  • At the 95% confidence level, no consistent or substantial evidence (yet) exists that recent rates of rise are higher or abnormal in the context of the historical records available for the United States.
  •  It is likely that a further 20 years of data will identify whether recent increases east of Galveston and along the east coast are evidence of the onset of climate change induced acceleration.

The magnitudes of observed rates of sea level rise and accelerations are relatively small compared to those associated with predicted scenarios of 21st century sea level rise (e.g. IPCC, NOAA). Under various forecast scenarios, the current rate of global averaged sea-level rise of ~3 mm/yr is expected to increase to rates of the order of 10–20 mm/yr or more by 2100.

Figure 7 from Watson (2016) provides a visual analysis of how the velocity and acceleration time series might change at San Francisco and New York based on a mean sea-level rise of 80 cm from present (2014) to 2100. This analysis provides a sense of perspective regarding the changes of mean sea level at these locations to give effect to meet these projections.

8. Conclusions

The implications of sea-level rise, particularly the much larger projected rates of rise under future climate change scenarios (e.g IPCC, NOAA) are profound, with far reaching socioeconomic and environmental implications.

The Mississippi delta and many barrier islands will undoubtedly undergo marked changes in the future, with or without global warming.  Land use and engineering in the major coastal cities have brought on many of the worst problems, notably landfilling in coastal wetland areas.

The most vulnerable locations are developing comprehensive adaptation plans, notably Florida and New York City.  There are no easy solutions and no obvious scapegoats to blame, in spite of the numerous sea level rise related global warming lawsuits (see previous blog post The blame game).

But the bottom line remains that in many of the most vulnerable locations, natural oceanic and geologic processes and land use practices are the dominant causes of local sea level rise problems.  Sea level will continue to rise in the 21st century. The more extreme scenarios of 21st century sea level rise from human caused global warming would dominate local sea level rise pretty much everywhere, but the smaller values such as the likely range from IPCC RCP4.5 scenario would not dominate local sea level rise in many locations.

What surprises me is that there seems to have been so little general awareness of the sea level rise issue until several decades ago.   Mean global sea level has risen at a slow creep for about 150 years.  The cumulative impact of local land use impacts is driving awareness in the most vulnerable locations, even though the popular discourse tends to blame these problems on human caused global warming.

In terms of adaptation strategies in the face of uncertainty in 21st century sea level rise projections, the issue becomes how much resilience can you afford? Wealthy places like Miami Beach will pull out all the stops to adapt to this.  Large cities with major infrastructure on vulnerable coasts (e.g. the San Francisco airport) will need to consider the sea level rise in their next generation infrastructure plans.  Other locations (e.g. deltas, barrier islands) will need to acknowledge that unavoidable changes are coming.


96 responses to “Sea level rise acceleration (or not): Part VII U.S. coastal impacts

  1. Reblogged this on Climate Collections.

  2. David Wojick

    This series combined would make a great monograph.

    Regarding this statement at the end: “What surprises me is that there seems to have been so little general awareness of the sea level rise issue until several decades ago.”

    The reason is primarily political. Global warming sort of dies out over the last few decades, especially with the grand pause, and climate change is also not showing up much. But sea level rise is continuing unabated so it naturally becomes the focus of the scare stories. It is these stories, not the rise, that raises the issue, especially the exaggerated ones.

  3. Thank you for a very helpful post. Very useful to have the relevant IPCC analysis. An additional concern I have is the level of uncertainty with SLR figures. I am aware of the legion of difficulties in measuring sea level since 1880, let alone on any particular day. Yet the current levels of uncertainty given by NOAA or Berkeley Earth and others are incredibly small in terms of tenths of an inch and even hundredths And the IPCC uses meaningless, ambiguous, unquantifiable terms. As a layman, what do I trust? How do I know what they really know?

  4. David Wojick

    You say at the end “Sea level will continue to rise in the 21st century.” If this means throughout the 21st century then it strikes me as a speculation. Might not a massive global cooling stop it? Or tectonic changes, etc.? We do not know that this will not happen.

    • There is a lot of memory in the system, this won’t turn on a dime.

      • David Wojick

        Memory of what? Are you assuming that you know why sea level rise is occurring? I hope it is not based on surface warming because I doubt that has actually happened.

      • “…I doubt that has actually happened.”

        Even for a committed skeptic like me, that is quite a statement.

        What I have a hard time swallowing is that by some extraordinary coincidence, acceleration of SLR has occurred exactly to the year when a new system of measurement was implemented.

        Other than coastal subsidence/geological processes, my sense is that relative SLR will be more benign than all the scare stories would make one believe. There are many unknowns about what the ocean basins are capable of doing to mute the impact locally, regardless of warming temperatures.

      • Read it again.

      • Steric sea level rise doesn’t need surface warming, it only needs a surface that is warmer than an equilibrium state. As long as SSTs are warmer than they were in the late 1800s, when modern sea level rise began, we can expect to see some level of rising seas. The change to a new equilibrium appears to be hundreds of years away, so that’s not going to happen either. That’s what folks don’t get about a warming ocean (including Javier’s good buddy Leif). Ocean heat content has continued to rise unabated even during the hiatus in surface warming…

      • In terms of inches or millimeters of projected sea level rise, the numbers aren’t terribly dramatic (other than at higher IPCC RCP scenarios}. But the truth of the matter is that slr carries life-changing importance at many localities detailed in Dr. Curry’s paper. Miami is going to have to take very expensive measures soon – so is New York City.

        And there are multitudes of small communities facing these problems. Swan Quarter NC is a fishing community built a century ago a few feet above sea level. They have already built a dike to protect farm land from salt water intrusion. Many NC communities were built virtually at sea level and the slow march of slr has created problem that has to be dealt with immediately. Like on the Mississippi Delta, some of these communities will simply move a few feet higher and some will gradually disappear. But the NC coastal plane is huge, and there aren’t many places to go that are higher.

        Atlantic Beach NC is fortunate to have the Corps of Engineers supply sand for beach renourishment. The sand is dredged from Morehead CIty harbor and placed on the beach as the least cost disposal option. And some of the beach communities have chosen to tax themselves to raise funds for renourishment projects.

        This brings up the issue of who is to bear the cost. Is slr and beach erosion to be viewed as a local matter, placing the burden of mitigation on cities and counties (with some state assistance)? This is more like to happen in wealthier communities blessed with strong local leadership.

        Or is the matter to be viewed as primarily anthropogenic, thus placing more pressure on federal government? Smaller local projects have usually been financed locally, with state support and perhaps some federal support through loan guarantees. But we’ve heard discussion of building a sea wall around Manhatten Island, requiring financing on a different order of magnitude.

      • Great Series Judy!

        Indeed there is a lot of memory in the system and groundwater is the critical factor. A recent paper by paleoclimatologist looks at fluctuating sea levels when the earth was hotter and no ice caps or glaciers existed.

        “Sedimentary noise and sea levels linked to land–ocean water exchange and obliquity forcing”

        I posted and WUWT here on that same groundwater issue as measured in modern times.

    • “Sea level will continue to rise in the 21st century.”

      The future is unknowable but I consider this one of the safest predictions in climate science. Sea level has been increasing since 1850, when many glaciers all over the world starting melting, and has continued through periods of cooling like the 1900’s Gleissberg solar minimum, and the 1950-1975 Ice Age scare. What changes is the rate of sea level rise. Sometimes a little faster, sometimes a little slower.

      The conservative prediction is that “Sea level will continue to rise in the 21st century.” Any other prediction is far riskier. Obviously one day sea levels will stop rising, but chances are we won’t see that day.

      • Javier ==> Almost certainly correct. As it stands today, we are only guessing at the underlying causes of SLR, but we do know that it has been rising, at least on the century time scale, and that it [average global sea surface height] has NOT been rising at any rate that could be rightly labelled “dangerous”.
        Given that the rate is so even over the long term, it is highly unlikely that it will stop rising or that the rate will change in any real significant way.
        It is this last characteristic of global SLR — its unchanging rate over the century scale — that I consider the most telling.
        Localities that have serious problems with local relative sea levels are not dealing with the larger question of global rise of sea surface heights, but
        with localized problems of subsidence.
        [ There are a few incidents of just plain idiotic siting of cities at the sea level confluences of major rivers — Canton is a good example. ]

  5. Through daily surging wave action the high watermark on any beach varies up and down the sand by about a meter or so every 10 minutes. The official figure of sea-level rise is 1mm per year, presumably due to AGW. So to that daily high water mark of 1-2 meters let’s add just 1 millimeter per year, the thickness of a grain of sand. If the thought of that tiny extra bit of water creeping up the beach over the course of a year is terrifying anyone, i.e. 4” per century, perhaps psychiatric treatment can be recommended.
    You would think that “sea-level rise” was well documented, considering alarmists seem so sure that it is happening, but virtually nothing is to be found in literature or on the internet about the expansion properties of saltwater in association with atmospheric greenhouse gases. Water expansion is not uniform but exponential and greater closer to boiling, so height-rise of water is much less at lower temperatures. Salt water, being heavier, is slower to expand when heated, further reducing expanding of oceans at lower temperatures.

    • In many coastal areas, sea level has risen slowly but inexorably, endangering many developments that, by objective standards, never should have been placed there in the first place. If the area has become very valuable, then you will see a lot of money spent to try to mitigate the problem.

      To these communities, sea level rise is not an academic or scientific problem, and there’s little if no reason to believe that slr won’t continue to be a problem throughout the 21st century.

      • They’ll consult the Dutch; they won’t like what the Dutch say.

      • JCH – not sure what you mean. Some may think a dutch-scale infrastructure effort is overkill, but they haven’t closely looked at the realities. Miami is pretty much out of time. The entire east coast of Florida is facing the same thing, but Miami is front and center due to its large population and the fact that its barrier island has been concretized from one end to the other.

        I think we can be confident that slr threatened communities – at least those like Miami who have the wherewithall to do so – will spend what is necessary to protect themselves. Look at for a hard-headed look at the inevitable.

      • I think a lot of people think we will simply do what the Dutch did, and not even the Dutch think they can do that.

      • Many of these communities and infrastructure should simply not have been placed where they have been, as SLR is very long established in some areas

        In the UK the Environment Agency can advise, but can not demand that the local authority refuse planning permission for a development

        The result is that developers buy up the vulnerable land because people like living near the water, will pay a premium and expect ‘someone’ to protect them.

        Of course the situation can be made worse for existing residents as the flood plain will no longer exist


      • Sea level cannot simply go up without a reason. If anything, since ACO2 is not a control knob and the ice age was coming, developers had reasons to suspect levels would be dropping.

      • JCH

        Brilliant! Of course with the ice age coming sea levels will drop and thus much more prime land will become available that had previously been covered in sea.

        There is some land around our coasts that was only inundated as recently as 8000 years ago. It is known as Doggerland. It is a prime candidate for thousands of luxury homes

        As it is your idea perhaps we can set up a joint development co to exploit the land?

        One fly in the ointment is that the crown estates own all exploitable resources below the mean sea level thanks to Magna Carta.

        I will need to check the legal situation and run it past Prince Charles.


      • JCH and others. Miami and environs became heavily developed long before anybody even thought of slr. But the fact is that Miami is where it is. And they will spend whatever it takes to preserve it. The beach can be renourished into the future regardless of slr. There is an endless supply of sand on the coastal seabed, and Miami can build up another mainland if they want.

      • Ice Age Coming

        I noted in the USA TODAY a column calling for a shortened Baseball season since so many games have been postponed this Spring due to cold and snow.

        Could it be that America’s pastime is the Canary in the Coal Mine and some farsighted individuals know something the rest of us don’t?

        What’s next? Using a red golf ball for playing in the snow?

  6. 1/36 of an inch per year will add in a 100 years (~3 inches?), and in areas where the land is sinking — what with the easily anticipated high tides and the inevitable big storms — nature is as nature does and may offer-up some difficult challenges but… what can we do other than do whatever we can to adapt? Rich folks will continue to build fabulous houses on sand in desirable areas and leave their property to others who lack the wealth to maintain it or prevent the seas from reclaiming it.

  7. The average elevation of New Orleans is currently between 1-2 feet below sea level, with elevations ranging from 20 feet above sea level to 7 feet below sea level.

    Dr Curry, I think that you’ve got this backwards. The french quarter is considered to be the highest in the city at 7 feet which is why they built there. As you go away from the river and toward lake ponchartrain elevation gets lower and lower. If you remember images from katrina, with water up to roof tops, those houses were near the lake. (residential areas all along the river stayed high and dry)…

  8. 6. Coastal cities

    Also, you might want to add Miami to your list there (☺)

  9. Living on the barrier island in north Fort Lauderdale directly on the Atlantic east of the intercoastal, SLR has been a matter worth much personal scrutiny. Our buildings were constructed 1996-2000 to ‘Andrew’ hurricane standards. That also means surviving (without damage) storm surge that exceeds by many feet anything SLR can throw at us in the next century. What was just done (at a cost of about $55 million) was a major beach restoration from Pompano down to Sunrise Ave in central Fort Lauderdale. The problem is simple and unrelated to SLR. The large boat channel from the intercoastal to the Atlantic in north Pompano completely blocks the natural slow south flow of sand. So the beach south of that channel slowly erodes over a stretch of about 7 miles, and what was ‘our’ sand ends up in a very overly wide beach just north of the entrance to Port Everglades at the southeast end of Fort Lauderdale. (And ditto eroding beaches south of Port Everglades, but the local solution there is to ‘mine’ the overly wide north side and deposit on the south side.) About 145 million cubic meters of sand was mined from an ancient beach dune ridge west of Lake Okeechobee, trucked ~100 miles to the beach (total of ~80000 truckloads), and spread using heavy wheeled mining equipment from multilple temporary access points converted from local beach parks. This was not done haphazardly. The engineering and surveying took over two years before getting permitted by Army Corps of Engineers and state authorities. Done in ‘winter’ over 8 months outside the sea turtle nesting season. Done to a precision of about 6 inches vertical and one meter lateral into the ocean using laser placed survey stakes about every 20 meters. Raised the beach about a meter and about doubled its width at our place. Plus an artificial dune averaging 6-8 feet was built continuously along the inland (built up) side of all ~7 miles of the restored beach, planted with sea oats and sea grape, respectively deep rooting very salt tolerant native dune plants to hold the new dune against hurricane waves and storm surge.
    The only places where Irma caused problems last fall along A1A (the beach road) were mainly south of where this new artifical dune stopped. Along the A1A ‘strip’ between Sunrise and Los Olas, Irma piled sand 4-8 feet deep onto A1A itself. Took two months of big wheel loaders to put it all back on the beach. Local problem, local solution, paid for by surcharges to tourist hotel rates.

    • The NOAA graph shows NYC SLR dropping like a rock for the last 8 years. Maybe that trend should be revisited.

      • It should be the exact same data averaged that time period. NOAA uses PSMSL data.

      • nobodysknowledge

        I think Atlantic air pressure gradient (as NAO) has some impact on NYC SLR.

      • nobodysknowledge

        And storm surges show up in SLR data too.

      • nobodysknowledge

        From: Decadal Shift of NAO-Linked Interannual Sea Level Variability along the US Northeast Coast. Jessica S. Kenigson* and Weiqing Han
        “Here we use a robust method, Bayesian Dynamic Linear Modeling (DLM), to explore the non-stationary NAO impact on NEC sea level. The results show that a spatial pattern change of NAO-related winds near the NEC is a major cause of the NAO-sea level relationship shift. A new index using regional sea level pressure is developed which is a significantly better predictor of NEC sea level than is the NAO and is strongly linked to the intensity of westerly winds near the NEC. These results point to the vital importance of monitoring regional changes of wind and sea level pressure patterns, rather than the NAO index alone, to achieve more accurate predictions of sea level change along the NEC.”

      • From 1986 through 2016, what does this add up to?

      • Recently I was looking at the SLR data for Halifax, about 600 miles up the coast from NYC. I noticed an anomolous 10cm rise in 2010 which correlated to an abnormally low sea level pressure that year. The funny thing was that the next year the pressure returned to normal but the sea only dropped 5cm and has been stuck there abouts since. Was wondering if we had entered a different circulatory mode.

      • nobodysknowledge

        Good question climaeadj. Could it be a couple of storm surges more that year?

      • Robert I Ellison: Assuming it is white noise – it adds to zero.

        For white noise, the Expected Value is 0. The observed values over any finite time span may sum to a positive or negative number, but almost certainly do not sum to 0.

      • It isn’t white noise – duh.

      • Robert I Ellison: Assuming it is white noise – it adds to zero.

        Robert I Ellison: It isn’t white noise – duh.

        Assuming it had been white noise, it wouldn’t have summed to 0 over any finite interval. “White noise” seems to be a red herring in this instance.

    • JCH ==> NOAA CORS project has the Battery subsiding (sinking) at a rate of at least 1.3 mm/yr.
      The current long-term rate of local relative Sea Level Rise there is an official 2.84 mm/yr. Subtracting the VLM to get actual rising of the sea surface at the Battery, it comes to 1.5 mm/yr, less than the long-term global average.

      • My number is the last 30 years. Yours is pointless.

      • nobodysknowledge

        How much is The Battery sinking? You can get what you want:
        New York 1900 – 1999: Tide Gauge up 3,00 mm/year. (+/- 22%?)
        Vertical GPS: -2,12 gives sea level rise (SLR) 0,88 mm
        CSIRO GIA: -0,88 gives SLR: 2,12 mm
        Peltier ICE-6G: -1,80 gives SLR: 1,20 mm
        30 year intervals with SLR corrected for land movement (vertical GPS):
        1897 – 1926: -0,39mm/year
        1927 – 1956: 2,74mm/year
        1957 – 1986: 0,04mm/year
        1987 – 2016: 2,15mm/year

      • nobodysknowledge

        As DeWitt Payne posted at SoD:
        Not surprisingly, the low SLR rates coincide with negative phases of the AMO Index and conversely.
        A sine wave fit to the AMO Index data from 1856 to the present has peaks at 1878, 1944 and 2011. The minimums are 1911 and 1978.

  10. Great balanced summary.

  11. The study of sea-level changes by non-oceanographers is rife with basic misconceptions and methodological issues. I’ll start worrying about it only when Scripps Institution decides to sell its lower campus at a discount from prevailing La Jolla beachfront values.

    • It doesn’t take an oceanographer to figure out that sea level is rising. It has been for over a century and a half for obvious reasons. How much in the future is hard to figure, but rise it will.

      Dr. Curry figured this all out by herself.

  12. This seems to me like an obvious case where government is worsening a problem. By providing flood insurance for those living in low lying areas, they encourage continued development there. Rebuilding after a storm or hurricane is not something government wants to encourage it seems to me if you are in a low lying area.

  13. The threat of sea level rise here in the states should be rightly greeted with a yawn. We’ve already seen wholesale abandonment of infrastructure due to demographic changes. If the populace can (and has) handled that, then they should have no trouble adapting to changes brought about by sea level rise. Take Detroit for example. It was a city of two million people before its decline starting in the 1950s. Now it houses but a third of that. (at least with slr areas will eventually become uninhabitable, unlike detroit, which would actually be a plus) And demographic tides don’t stop rising and know no bounds. Here in New Orleans white flight began in the sixties with the populace moving west of the city to Jefferson Parish. Over subsequent decades the african american populace followed suit. This brought on a new wave of white flight to St Tammany Parish north of Lake Ponchartrain starting in the nineties. So this is a relatively quick process that never ends. People move. (always have, always will) If people see that sea level rise is a problem for themselves, then they will either adapt if they can or just move. Point being that we shouldn’t be acting as though this sort of thing hasn’t happened before…

  14. Here’s the estimated global annual groundwater recharge rate:

    How has this changed and how is it changing?

    Given the ever increasing amount of anthropogenic “impervious surface” on earth, what portion of precipitation over land is now finding its way into the oceans instead of recharging land based aquifers?

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  16. In regards to this issue: “The Report concludes that the U.S. coastal cities are close to a tipping point with respect to flood frequency, as only 0.3 m to 0.7 m separates infrequent damaging-to-destructive flooding from a regime of high tide flooding—or minor floods from moderate and major floods.”
    What this really means is that coastal infrastructure has been knowingly built within 1 to 2 feet of the “risk of flooding” line — (the datum (Highest Astronomical Tide) — in some cases, the land has subsided to be within that danger zone.
    Miami and Miami Beach, Florida are a striking example, with one major intersection built below normal highest high tide.
    Full-sized modern cities have been built on the barrier islands of the Carolinas — whole neighborhoods on New York’s Long Island and Staten Island have been built on historic tidal mud flats.
    The truer picture is that all of these areas already exist under threat of inundation and destruction resulting from the storms of today — as evidenced by repeated damage to these areas in the past. The < 1 foot of sea level rise over the last 150 years is not the cause of their predicament — it is Man's foolishness in building in these areas in the first place.

  17. “Wealthy places like Miami Beach will pull out all the stops to adapt to this. Large cities with major infrastructure on vulnerable coasts (e.g. the San Francisco airport) will need to consider the sea level rise in their next generation infrastructure plans. Other locations (e.g. deltas, barrier islands) will need to acknowledge that unavoidable changes are coming.”
    Miami Beach is already a “disaster-in-waiting”. The next strong hurricane causing steady strong winds from just the wrong direction will push 10 or more feet of water into the bay and flooding will be massive and catastrophic.
    San Francisco should begin now to raise runways at its airport, one at a time, by six to eight feet. The City and the other Bay Area cities need to change land use codes to stop any further development of low lying bay-front properties and forbid land-filling in the Bay.
    The southern East Coast barrier islands should be returned to their natural state after storms wreck homes and cities — nothing should be allowed to be rebuilt there. Eventually, the barrier islands will revert to their former state being in which they are allowed to move about and change their shapes as nature dictates. Declaring them all national parks, national seashores or wilderness areas is a good idea to prevent any further foolish development.

    • Kip, what would you say to those people out there who would say that many areas of the country have the same (or greater) risks than flooding? Metropolis’s built on fault lines and townships built in tornado alley come to mind. At least, when in comes to flooding, folks have a better chance of getting out of harm’s way. Now i’m probably not the guy to be making that argument, but you know he’s out there. (“well, mister hansen, you sure are holier than thou, aren’t you?”) i do think that they make a valid point, although i see no harm in government intervention to minimize risk…

      • Fonz ==> I would say, to the folks living on the Barrier Islands, that if their homes are destroyed by a hurricane sweeping the island clean, that they can not rebuild. They may collect their insurance money — but just once more — and build elsewhere.
        I would say the same to anyone who has a home in a known recurrent flood plain (many areas already have laws and codes that forbid new construction in FEMA designated flood zones), on landslide prone critical-sloped hillsides in Southern California, on land-fill-created artificial islands with (altitudes of 2 or 3 feet) turned into housing developments (Florida, California, Gulf-coast).
        I would not say the same to houses in “Tornado Alley” because Tornado Alley is not a physical thing, but a construct of history (where tornadoes have hit in the past)….but insurance rates should intelligently take likelihood of tornado damage into account.
        All along the Southern East Coast of the United States, laws are being enacted and building codes are being modified to correct past poor decisions on these issues — permanent structures should not be built on impermanent sand bars. Hunting/fishing shacks, rough vacation beach cabins were appropriate 50-75 years ago, and that’s all people built. If they got washed away, people either rebuilt then or not, their choice.
        Depending on the rest of society to pay for (taxes, federal flood insurance, etc) your two million dollar second vacation home on the Atlantic side of a Carolina barrier island should not be allowed. The construction should not have been allowed in the first place.
        The real bottom line is Too Many People, Too Much Expensive Infrastructure in the Wrong Places.

      • Kip, amen. Biggest issue IMO is not barrier islands, it is flood plains. Houston being a memorable recent example. Some homes there have been rebuilt 4 times in the past few years!

    • I think you’re right about the rebuilding, but you forget that 100 years, even 50 is a long time in a built up area. For some, getting two generations of use and enjoyment from a beach house is worth the expense.
      I live in one of the coastal, east coast, areas. These areas are subsiding, so planning for gradual rise in the high tideline is necessary regardless of SLR.
      Risk wise, the big concern is the ability to evacuate the growing crowd of tourists and year-round residents. We get a lot of early notice of hurricanes, but it takes a long time to move thousands of people out of an area.
      Secondly, there’s the related problem of that long, long hurricane drought. Here in Virginia there are thousands of residents who have never experienced a hurricane and have no idea what they can do. I saw a neighbor leave their pool umbrella out, opened, in the last near miss. That person is going to be hard to convince to evacuate. And is going to be hard to get out of the area due to population and tourist growth here. Ten years of telling people every year they were going to have an “above normal” hurricane season that resulted in nothing didn’t help that situation.
      To adequately follow the precautionary principle, the California bay area needs to be built for a 30-foot tsunami.

      • Jeff ==> My wife and I sat out Hurricane Irene (august 2011) on our sailboat in a tiny marina just north of Beaufort, NC — a direct hit for us.
        The Outer Banks (Hatteras) has several new islands created by cutting the banks with new inlets.
        I think the Bay Area of San Francisco will be spared much tsunami damage as any tsunami will have to pass through under the Golden Gate Bridge – a small opening spreading out into the much larger bay which would dissipate (not eliminate) the force and wave. The Sacramento River Delta is subsiding, as all deltas do, and really should be left as farmland — not build upon.

      • Kip

        I can’t imagine what riding out that storm was like. A friend rode out a Florida Hurricane in a well built house several miles from shore. He said it was the scariest night he ever experienced and would never do that again.

      • i imagine that was a wild ride!
        One thing local governments could do about buildup in hurricane prone areas is require insurance to cover the cleanup of debris post hurricane. A buddy’s bay-front house was next door to a house that was totally destroyed- washed into the bay – by Isabel in 2003. We’re still pulling pipes, broken glass, wire, and boards with nails out of the water 15 years later. And yeah, they rebuilt. Right in the same wash. Bigger house.

  18. One has to remember that virtually all infrastructure in cities is less than 100 years old. As sea levels rise over centuries, the new buildings/sewers/roads will be moved or built higher, as they have been in the past. Thus the largest part of the cost to protect coastal cities is zero.

    Places like NYC also have the capability to build a sea wall. The Dutch did in a 1950 economy to protect an area 10x bigger than NYC. The cost for the rich people of NYC is negligible.

  19. Dr Curry, thank you again for another good essay. Combined, your SLR essays might make a good paper for a review journal.

  20. 10% of the evaporation that happens over the ocean becomes precipitation over (only 64% of water precipitated over land evaporates, oceans evaporate more than 100% of the water that falls into them) . Therefore increased IR will cause a net transfer from the ocean to the land. Greening from both warming and CO2 fertilization should lead to increased retention of water in the land biosphere and increased water available to replenish aquifers which aren’t at capacity.

    Whether melting glaciers end up in the ocean or retained on land is also highly uncertain for the same reasons.

    • Land use is likely a bigger factor in sea level rise than warming. We can foster retention of water on land.

    • There was a recent paper that suggested runoff will increase because plants will be using less water.

      • With plants using less water, the aquifers will have more of it.

      • So will the sea.

      • I’ve suggested the same in the past, but it also means more water available for other plants, soils, and aquifers. We can also determine whether it becomes run off.

      • “So will the sea.”

        More parking lots, more runoff to the sea?

      • E.G. We can increase retention and open up access to aquifers that have been paved over in LA region. The aquifers are contaminated currently. We can dilute the contamination and slowly flush them out and return them to use. Increase retention of water on land, clean up pollution, and decrease demand on the Ogallala aquifer. Kill three birds with one stone.

      • Four birds. Also reduces flooding in extreme rain events.

      • We can increase river throughput near big cities or go to the sources. We need water retention closer to the sources which is everywhere not in the big cities. Whether or not Minnesota becomes a sun baked hell because of global warming, we want good water management and non-depleted aquifers. Wind turbines and solar ain’t doing much for our water quality.

  21. David Wojick

    Has anyone considered that some, or even all, of the observed SLR is simply due to tectonic changes in the volume of the ocean basin? The global plates, ridges and sea mountains are everywhere in motion, horizontally and presumably vertically as well.

    They are after all just a thin film on a circulating molten mass. A few hundred miles thick, perhaps well less than that in places (I forget the facts here), out of 8000 miles..That the geometry of the basin should not change over time seems highly unlikely.

    • If you are desperately reaching for an explanation for sea level rise other than warming, congratulations. It’s possible. But how likely is it that the global plates, ridges mountains, molehills etc. have been moving up, down and around in such a way as to create the steady rise in seal level? Intelligent design?

      • David Wojick

        Considering there has been almost no warming since satellite records began, just 0.3 degrees C in a single quick step, I think other explanations are called for. In fact the steady SLR is completely out of step with the single step temperature rise.

        My vague recollection is that in California the Pacific plate is sliding along the North American plate at something like 3 cm per year. How steady has that been? The overall sliding that is, not the stops and slips where local earthquakes occur. I would imagine that the tectonic motions are pretty uniform on the century scale, it being so small. Plates and ridges do not jump around.

      • Considering there has been almost no warming since satellite records began

        A tired, tedious attempt at cherry picking which is transparently deceitful in ignoring the inconvenient surface record and blatantly untrue in that the linear trend of your cherry picked data is almost double what you claim it is.

        You’re actually paid by CFACT for this deceit, too, aren’t you?

        Nice work.

      • Do you think that glaciers and oceans heat up in a quick step? What is your frame of reference for 0.3 C being almost no warming? Your bathwater?

        You are making the wrong arguments and clowning yourself.

      • I don’t think it’s deceit. It’s deep denial.

      • But how likely is it that the global plates, ridges mountains, molehills etc. have been moving up, down and around in such a way as to create the steady rise in seal level?

        Moving of the plates is several orders of magnitude more likely to have created measurable changes in sea level than one molecule of manmade CO2 out of ten thousand molecules in the atmosphere. That is what is not likely.

      • Nice assertion, popesy. Write it up and submit it to a denier friendly journal. The part about one in ten thousand molecules is especially assertive. That actually made some sense to me, when I first heard it about 12 years ago. I am not so stupid now. Good luck.

    • Has anyone considered it could be that underwater unicorns have increased their rate of urination, David?

      • David Wojick

        Not to my knowledge, but tectonic motions are everywhere and often larger than SLR. You do understand that the continents and seabeds are all in motion, right? Unlike the unicorns.

      • Wait, the underwater unicorns don’t move around? What are their legs for then?

      • David, you’re so deep in denial you might emerge in China. Has anyone asked if it’s your underground motion causing those tectonic shifts?

    • Research suggests the opposite is happening at the moment. Estimates of increasing ocean basin are used to determine sea level rise in satellite data. This is supposed to be the reason sea level has not been rising lately.

  22. Arthur E-mail

    I live in NYC, near the Brooklyn beaches. NYC may have developed plans, but there is no money being spend of any significance that is happening to reduce tidal flooding. Lots of talk and studies associated with researchers working for the Core of Engineers. At community meetings we are told more modeling studies are going on and will continue to happen, but no tidal mitigation measures ever get built. Now nearing 6 years after Sandy, the entire process seems like a scam on the working people of NYC who pay excessive flood insurance premiums.

  23. Cities themselves rise at ~ 5mm per year, at least 5mm / yr faster than sea level rise.

  24. Obviously the coasts are made of flubber, and seawater just bounces off them. The aquifers are refilling with pure water, and the mountains are made of rock candy.

    • Do you deny that cities rise over the centuries?

      Obviously archaeologists who dig down to find historical human dwellings are all Koch brothers funded conspirators digging to undermine sea level rise alarmism.

  25. You wrote: mainly as a result of mean sea level rise due in part to anthropogenic warming

    There is no proof that any sea level rise is due to anthropogenic warming.
    There is no proof that any warming is due to manmade (anthropogenic) CO2 or to natural CO2.

    Mainly as a result of anthropogenic warming is totally without support by any data of any kind. (model output is not any kind of data)

    You wrote: What surprises me is that there seems to have been so little general awareness of the sea level rise issue until several decades ago.

    Chicken little had no need for a new scare before then.

    Rome had a harbor entrance, 2000 years ago that is above sea level now. Isle of Capri had the Blue Grotto cave entrance at sea level that is still at sea level.

    Some places have local sea level that is rising and they have many tide gauges measuring this. Some places have local sea level that is falling and then don’t need or want to measure it. The alarmists average these gauges together and only get the data included from rising gauges.

    • The uncertainty in temperature measurements and the uncertainty in sea level measurements and uncertainty in knowing how to average them together is much larger than the changes in the measurements.

  26. Wind and flood stories … in 1981, we lived in a tiny caravan high on a 38-acre block inland from Queensland’s Sunshine Coast. We got home one day to find it had burned to the ground. We moved a forestry barracks on to a ridge on the block, we could see 10-11 miles to the West. We moved straight in, the building was sitting on piles of railway sleepers, not anchored. That night, a cyclone crossed the nearby coast for the first time since 1974 (when Brisbane had massive floods). The intensity peaked 1-3 a.m., massive wind. We sat waiting for what might happen, fearing the house would be blown off the timber piles – nothing. I said that if the house can withstand a cyclone while not tethered to the ground, it should withstand anything. At least it wasn’t prone to flooding!

    Although three or four days before my wife was due to have a Ceasarean one Friday in January 1982, the nearby Mary River flooded, it came up our valley and we were flooded in. Come Thursday, no change. I said to Helen, “Home births are one thing, kitchen table Caesarean’s another.” Fortunately the floodwater receded that afternoon.

    We expected to be hit by the massive (and largely caused by government mismanagement) flood in Brisbane in 2011, it stopped four metres from our back door.

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