East and Gulf coasts of the US
This blog entry will be restricted to coastal sea level reports and papers relevant to the US east and Gulf coasts.
I've included papers on global SLR when it is very relevant to the geographic region. Otherwise, I'm going to stay focused [and that isn't easy]
I've provided links to open source reports and journal paper when available. You can always search for the title and often the authors have PDF's available.
I've included a the abstract from the paper or put a comment in brackets.
If you see a reference that should be added let me know.
Abstract - Motions of three hundred and sixty Global Positioning System (GPS) sites in Canada and the United States yield a detailed image of the vertical and horizontal velocity fields within the nominally stable interior of the North American plate. By far the strongest signal is the effect of glacial isostatic adjustment (GIA) due to ice mass unloading during deglaciation. Vertical velocities show present-day uplift ( 10 mm/yr) near Hudson Bay, the site of thickest ice at the last glacial maximum. The uplift rates generally decrease with distance from Hudson Bay and change to subsidence (1–2 mm/yr) south of the Great Lakes. The ‘‘hinge line’’ separating uplift from subsidence is consistent with data from water level gauges along the Great Lakes, showing uplift along the northern shores and subsidence along the southern ones. Horizontal motions show outward motion from Hudson Bay with complex local variations especially in the far field. Although the vertical motions are generally consistent with the predictions of GIA models, the horizontal data illustrate the need and opportunity to improve the models via more accurate descriptions of the ice load and laterally variable mantle viscosity.
William Sweet, Chris Zervas, Stephen Gill. 2009. Elevated east coast sea levels anomaly:: July – June 2009. NOAA Technical Report NOS CO-OPS 051. Link to PDF [This report refers to many earlier papers on sea level studies]
From their summary - CO-OPS stations recorded higher than normal sea levels (SL) along the U.S. East Coast in June and July 2009. Near-peak levels in the latter half of June coincided with a perigean-spring tide, an extreme predicted tide when the moon is closest to the Earth during a spring tide. This tidal event added to the observed SL anomaly, produced minor coastal flooding, and caught the attention of many coastal communities because of the lack of coastal storms that normally cause such anomalies.....two possible mechanisms..... NE wind forcing and Gulf Stream slow down.
Jianjun Yin, Michael E. Schlesinger & Ronald J. Stouffer. 2009.
Model projections of rapid sea-level rise on the northeast coast of the United States. Nature Geoscience 2, 262 - 266.
Human-induced climate change could cause global sea-level rise. Through the dynamic adjustment of the sea surface in response to a possible slowdown of the Atlantic meridional overturning circulation, a warming climate could also affect regional sea levels, especially in the North Atlantic region, leading to high vulnerability for low-lying Florida and western Europe. Here we analyse climate projections from a set of state-of-the-art climate models for such regional changes, and find a rapid dynamical rise in sea level on the northeast coast of the United States during the twenty-first century. For New York City, the rise due to ocean circulation changes amounts to 15, 20 and 21 cm for scenarios with low, medium and high rates of emissions respectively, at a similar magnitude to expected global thermal expansion. Analysing one of the climate models in detail, we find that a dynamic, regional rise in sea level is induced by a weakening meridional overturning circulation in the Atlantic Ocean, and superimposed on the global mean sea-level rise. We conclude that together, future changes in sea level and ocean circulation will have a greater effect on the heavily populated northeastern United States than estimated previously. .
Church,John A. and Neil J. White. 2011. Sea-Level Rise from the Late 19th to the Early 21st Century. Survey of Geophysics. DOI 10.1007/s10712-011-9119-1 Link to Open Source
Since the start of the altimeter record in 1993, global average sea level rose at a rate near the upper end of the sea level projections of the Intergovernmental Panel on Climate Change’s Third and Fourth Assessment Reports. However, the reconstruction indicates there was little net change in sea level from 1990 to 1993, most likely as a result of the volcanic eruption of Mount Pinatubo in 1991.USCOE.2011. Sea-Level change considerations for civil works programs. USCOE Circular No. 1165-2-212. Link to PDF [these 'considerations' are updated annually I believe. USCOE has a SL tool to determine future SL at various locales]
Sweet, William and C. Zervas. Cool-Season Sea Level Anomalies and Storm Surges along the U.S. East Coast: Climatology and Comparison with the 2009/10 El Nino. Monthly Weather Review. DOI: 10.1175/MWR-D-10-05043.1. Link
Climatologies of sea level anomalies (.0.05 m) and daily-mean storm surges (.0.3 m) are presented for the 1960–2010 cool seasons (October–April) along the East Coast of the United States at Boston, Massachusetts; Atlantic City, New Jersey; Sewells Point (Norfolk), Virginia; and Charleston, South Carolina. The high sea level anomaly and the number of storm surges, among the highest in the last half century during the 2009/10 cool season, are comparable during strong El Nin˜ o cool seasons. High numbers of daily storm surges occur in response to numerous East Coast extratropical cool-season storms and have a positive correlation with the El Nin˜o phase of the El Nin˜ o–Southern Oscillation (ENSO). Patterns of anomalously high sea levels are attributed to ElNin˜ o–related changes to atmospheric pressure over the Gulf of Mexico and eastern Canada and to the wind field over the Northeast U.S. continental shelf.
Sallenger, Asbury H. Jr, Kara S. Doran and Peter A. Howd. 2012. Hotspot of accelerated sea-level rise on the Atlantic coast of North America. Nature Climate Change. PUBLISHED ONLINE: 24 JUNE 2012 | DOI:10.1038/NCLIMATE1597. Link to Journal (not open Source) [This paper was the first of many that started to look at accelerating sea level rise. Sadly, Abby died not long after this paper was published.]
Boon, John B.. 2012. Evidence of Sea Level Acceleration at U.S. and Canadian
Tide Stations, Atlantic Coast, North America. Journal of Coastal Research. DOI: 10.2112/JCOASTRES-D-12-00102.1 received 25 May 2012; accepted in revision 10 July 2012. Link to Open Source PDF.
Sea level data from the Chesapeake Bay are used to test a novel new analysis method for studies of sea level rise (SLR). The method, based on Empirical Mode Decomposition and Hilbert-Huang Transformation, separates the sea level trend from other oscillating modes and reveals how the mean sea level changes over time. Bootstrap calculations test the robustness of the method and provide confidence levels. The analysis shows that rates of SLR have increased from ∼1–3 mm y−1 in the 1930s to ∼4–10 mm y−1 in 2011, an acceleration of ∼0.05–0.10 mm y−2 that is larger than most previous studies, but comparable to recent findings by Sallenger and collaborators. While land subsidence increases SLR rates in the bay relative to global SLR, the acceleration results support Sallenger et al.'s proposition that an additional contribution to SLR from climatic changes in ocean circulation is affecting the region.NOAA. 2012. Global Sea Level Rise Scenarios for the United States National Climate Assessment. NOAA Technical Report OAR CPO-1. Link to PDF
Anna Cathey Linhoss, Lisa Gardner Chambers, Kevin Wozniak, and Tom Ankersen. A Multi-Disciplinary Review of Current Sea-Level Rise Research in Florida. Published by Florida Sea Grant. Link to PDF [read for detailed information on Florida specific papers].
John Hunter. 2012. A simple technique for estimating an allowance for uncertain sea-level rise. Climatic Change (2012) 113:239–252. [one of many important papers by John Hunter.
Abstract Projections of climate change are inherently uncertain, leading to considerable debate over suitable allowances for future changes such as sea-level rise (an allowance’ is, in this context, the amount by which something, such as the height of coastal infrastructure, needs to be altered to cope with climate change). Words such as ‘plausible’ and ‘high-end’ abound, with little objective or statistically valid support. It is firstly shown that, in cases in which extreme events are modified by an uncertain change in the average (e.g. flooding caused by a rise in mean sea level), it is preferable to base future allowances on estimates of the expected frequency of exceedances rather than on the probability of at least one exceedance. A simple method of determining a future sea-level rise allowance is then derived, based on the projected rise in mean sea level and its uncertainty, and on the variability of present tides and storm surges (‘storm tides’). The method preserves the expected frequency of flooding events under a given projection of sea-level rise. It is assumed that the statistics of storm tides relative to mean sea level are unchanged. The method is demonstrated using the GESLA (Global Extreme Sea-Level Analysis) data set of roughly hourly sea levels, covering 198 sites over much of the globe. Two possible projections of sea-level rise are assumed for the 21st century: one based on the Third and Fourth Assessment Reports of the Intergovernmental Panel on Climate Change and a larger one based on research since the Fourth Assessment Report.
Abstract - Impacts of ocean dynamics on spatial and temporal variations in sea level rise (SLR) along the U.S. East Coast are characterized by empirical mode decomposition analysis and compared with global SLR. The findings show a striking latitudinal SLR pattern. Sea level acceleration consistent with a weakening Gulf Stream is maximum just north of Cape Hatteras and decreasing northward, while SLR driven by multidecadal variations, possibly from climatic variations in subpolar regions, is maximum in the north and decreasing southward. The combined impact of sea level acceleration and multidecadal variations explains why the global mean SLR obtained from ~20 years of altimeter data is about twice the century-long global SLR obtained from tide gauge data. The sea level difference between Bermuda and the U.S. coast is highly correlated with the transport of the Atlantic Overturning Circulation, a result with implications for detecting past and future climatic changes using tide gauge data.
Ezer, T. L. P. Atkinson, W. B. Corlett and J. L. Blanco. 2013 Gulf Stream's induced sea level rise and variability along the U.S. mid-Atlantic coast, J. Geophys. Res., 118(2), 685-697, doi:10.1002/jgrc.20091, 2013. (AGU/Wiley Open Access: here
Abstract - Recent studies indicate that the rates of sea level rise (SLR) along the U.S. mid-Atlantic coast have accelerated in recent decades, possibly due to a slowdown of the Atlantic Meridional Overturning Circulation (AMOC) and its upper branch, the Gulf Stream (GS). We analyzed the GS elevation gradient obtained from altimeter data, the Florida Current transport obtained from cable measurements, the North Atlantic Oscillation (NAO) index, and coastal sea level obtained from 10 tide gauge stations in the Chesapeake Bay and the mid-Atlantic coast. An Empirical Mode Decomposition/Hilbert-Huang Transformation (EMD/HHT) method was used to separate long-term trends from oscillating modes. The coastal sea level variations were found to be strongly influenced by variations in the GS on timescales ranging from a few months to decades. It appears that the GS has shifted from a 6–8 year oscillation cycle to a continuous weakening trend since about 2004 and that this trend may be responsible for recent acceleration in local SLR. The correlation between long-term changes in the coastal sea level and changes in the GS strength was extremely high (R = −0.85 with more than 99.99% confidence that the correlation is not zero). The impact of the GS on SLR rates over the past decade seems to be larger in the southern portion of the mid-Atlantic Bight near Cape Hatteras and is reduced northward along the coast. The study suggests that regional coastal sea level rise projections due to climate change must take into account the impact of spatial changes in ocean dynamics.
Annually averaged sea level (1970–2012) measured by tide gauges along the North American east coast is remarkably coherent over a 1700 km swath from Nova Scotia to North Carolina. Satellite altimetry (1993–2011) shows that this coherent interannual variability extends over the Middle Atlantic Bight, Gulf of Maine, and Scotian Shelf to the shelf break where there is a local minimum in sea level variance. Comparison with National Center for Environmental Prediction reanalysis winds suggests that a significant fraction of the detrended sea level variance is forced by the region's along-shelf wind stress. While interannual changes in sea level appear to be forced locally, altimetry suggests that the changes observed along the coast and over the shelf may influence the Gulf Stream path downstream of Cape Hatteras.
Atkinson, L. P., T. Ezer and E. Smith, 2013, Sea level rise and flooding risk in Virginia, Sea Grant Law and Policy Journal, Vol. 5, No. 2, 3-14, 2013. Link to PDF
Kopp, Robert E.. 2013. Does the mid-Atlantic United States sea-level acceleration hot spot reﬂect ocean dynamic variability? Geophysical Research Letters, Vol. 40, 1-5, doi:10.1002/grl.50781, 2013
Consistent with the hypothesis that the regional sea level “hot spot” represents variability rather than the start of a trend, none of these indices currently exceeds its range of historical variability. As the changes in these indices have slowed over the last decade, if the indices reflect the driving factors underlying the “hot spot,” the phenomenon may not prove to be enduring.Zervas, Chris, Stephen Gill , William Sweet. 2013. Estimating Vertical Land Motion from Long-Term Tide Gauge Records. Technical Report NOS CO-OPS 065. Link to PDF
Eggleston, Jack, and Pope, Jason, 2013, Land subsidence and relative sea-level rise in the southern Chesapeake Bay region: U.S. Geological Survey Circular 1392, 30 p., http://dx.doi.org/10.3133/cir1392. [A key paper on subsidence on lower Chesapeake Bay]
Aquifer-system compaction may be responsible for the majority of land subsidence in the southern Chesapeake Bay region based on average measured land subsidence rates of about 2.8 mm/yr and measured average compaction rates of 2.6 mm/yr (table 3). The aquifer-system compaction is caused by high groundwater withdrawal rates that have lowered water levels
Higher summer air temperatures and lower winter temperatures and changes in atmospheric pressure causing larger tidal ranges. "The changes in the seasonal sea level cycle are shown to have almost doubled the risk of hurricane induced flooding associated with sea level rise since the 1990s for the eastern and north-eastern Gulf of Mexico coastlines."
from their summary - An analysis of geological and historical sea-level records shows a significant rate of increase in sea-level rise since the nineteenth century. In New Jersey, it is extremely likely that sea-level rise in the twentieth century was faster than during any other century in the last 4.3 thousand years. Accounting for regional and local factors, the authors project sea-level rise in the mid-Atlantic U.S. most likely about 38–42′′ (96–106 cm) over the twentieth century, but possibly as high as 66–71′′ (168–180 cm)
Boesch, D.F., L.P. Atkinson, W.C. Boicourt, J.D., Boon, D.R. Cahoon, R.A. Dalrymple, T. Ezer, B.P., Horton, Z.P. Johnson, R.E. Kopp, M. Li, R.H. Moss,, A. Parris, C.K. Sommerfield. 2013. Updating Maryland’s Sea-level Rise Projections. Special Report of the Scientific and Technical Working Group to the Maryland Climate Change Commission, 22 pp. University of Maryland Center for Environmental Science, Cambridge, MD. Link to PDF
VIMS. 2013. Recurrent flooding study for Tidewater Virginia. Link to PDF
Jianjun Yin and Paul B. Goddard. 2013. Oceanic Control of Sea Level Rise Patterns along the East Coast of the United States. doi: 10.1002/2013GL057992.
Abstract: Along the eastern seaboard of the U.S. from Florida to Maine, sea level rise (SLR) shows notable patterns and significant deviation from the global mean, which have been attributed to land subsidence. Consistent with several recent studies, we analyze various observation and modeling data, and find that ocean dynamics is also an important factor in explaining these coastal SLR patterns. Despite a southward shift since the 1990s, an overall northward shift of the Gulf Stream during the 20th century contributed to the faster SLR in the Mid-Atlantic region (North Carolina to New Jersey). In response to the 21st century climatic forcing, the rise (fall) of the dynamic sea level north (south) of Cape Hatteras is mainly induced by the significant decline of ocean density contrast across the Gulf Stream. This baroclinic process is the likely cause of the recent switch of the coastal SLR to a pattern with faster (slower) rates north (south) of Cape Hatteras.
Robert J. Nicholls et. al. 2014. Sea-level scenarios for evaluating coastal impacts. WIREs Clim Change 2013. doi: 10.1002/wcc.253. Link to PDF at Authors Institution [more good stuff from Nicholls]
M. S. Bos, S. D. P. Williams, I. B. Araujo and L. Bastos. The effect of temporal correlated noise on the sea level rate and acceleration uncertainty.
[Important rebutal of Ezer and others acceleration rates.]
Summary It is well known that sea level variations exhibit temporal correlation. This is sometimes ignored in the estimation process of the sea level rise or taken into account using a first-order autoregressive model. We have verified that this stochastic model is accurate for yearly tide gauge and sea level reconstruction time-series but it underestimates the real rate uncertainty in satellite altimetry and monthly tide gauge data by a factor of 1.3–1.5 and sometimes even 2. Similar results were found for sea level acceleration. An original finding is that in 13– 17 per cent of the tide gauge data, we found random walk which increases the rate uncertainty on average by an additional factor of 3. The estimation errors presented in this research should be added to the other sources of uncertainty, such as the vertical land movement, spatial correlation and altimeter drift, to obtain the total sea level rate and acceleration error.
Kenneth G. Miller, Robert E. Kopp, Benjamin P. Horton, James V. Browning and
Andrew C. Kemp A geological perspective on sea-level rise and its impacts along the U.S. mid-Atlantic coast. Earth's Future.Link to PDF
We evaluate paleo-, historical, and future sea-level rise along the U.S. mid-Atlantic coast. The rate of relative sea-level rise in New Jersey decreased from 3.5 ± 1.0 mm/yr at 7.5–6.5 ka, to 2.2 ± 0.8 mm/yr at 5.5–4.5 ka to a minimum of 0.9 ± 0.4 mm/yr at 3.3–2.3 ka. Relative sea level rose at a rate of 1.6 ± 0.1 mm/yr from 2.2 to 1.2 ka (750 Common Era [CE]) and 1.4 ± 0.1 mm/yr from 800 to 1800 CE. Geological and tide-gauge data show that sea-level rise was more rapid throughout the region since the Industrial Revolution (19th century = 2.7 ± 0.4 mm/yr; 20th century = 3.8 ± 0.2 mm/yr). There is a 95% probability that the 20th century rate of sea-level rise was faster than it was in any century in the last 4.3 kyr. These records reflect global rise (∼1.7 ± 0.2 mm/yr since 1880 CE) and subsidence from glacio-isostatic adjustment (∼1.3 ± 0.4 mm/yr) at bedrock locations (e.g., New York City). At coastal plain locations, the rate of rise is 0.3–1.3 mm/yr higher due to groundwater withdrawal and compaction. We construct 21st century relative sea-level rise scenarios including global, regional, and local processes. We project a 22 cm rise at bedrock locations by 2030 (central scenario; low- and high-end scenarios range of 16–38 cm), 40 cm by 2050 (range 28–65 cm), and 96 cm by 2100 (range 66–168 cm), with coastal plain locations having higher rises (3, 5–6, and 10–12 cm higher, respectively). By 2050 CE in the central scenario, a storm with a 10 year recurrence interval will exceed all historic storms at Atlantic City.
We conclude that regional-scale differences [in their case between Isle of Wight (UK) and North Carolina]of sea-level change highlight the value of using several, regionally representative RSL records when calibrating and testing semi-empirical models of sea level against palaeo-records. This is because by using records that potentially over-estimate sea-level rise in the past such models risk over-estimating sea-level rise in the futureT. Ezer. 2014 Uneven Sea Level Rise (SLR) along the U.S. East Coast: - The impact of ocean dynamics on past changes and future projections. Eposter for Ocean Sciences Meeting, Hawaii. Link
Chang, B., Guan, J., and Aral, M. (2012) Semi-Empirical Modeling of Spatial Variations in Sea Level Rise. World Environmental and Water Resources Congress 2012: pp. 1966 1971. doi:10.1061/9780784412312.197
Sea level rise is one of the important impacts of climate change. Accordingly, the projection of future sea-level has drawn a lot of attentions. The consensus is that the models based on physical processes may not yet predict sea-level changes with confidence. An alternative way to model global sea level rise is the empirical or semi-empirical approaches recommended in the literature. In this study, we extended the empirical model concept to incorporate spatial resolution to characterize spatial variations of sea-level rise and to investigate interactions among sea-level and sea surface temperature (SST) in different regions of the world's oceans. In our model, the world's oceans are divided into 4 regions, and both rate of sea level rise and rate of temperature change for each region are proposed to be linearly correlated with sea-level and sea surface temperature of the 4 regions. This empirical model is calibrated using published spatial sea-level data and sea surface temperature records from 1950 to 2001, and the model fit matches historical records well. Based on the calibrated parameters, both sea level and temperature of Gulf of Mexico have relatively different characteristics from those of the other 3 regions. The calibrated model indicated that sea-levels of the four regions all rise significantly in the 21st century but not at the same level. The proposed model is an alternative to existing studies in the literature.T. M. Cronin, J. Farmer, R. E. Marzen, E. Thomas, and J. C. Varekamp. Late Holocene Sea-Level Variability and Atlantic Meridional Overturning Circulation. Paleooceanography. 29(4). DOI: 10.1002/2014PA002632
Pre-20th century sea-level (SL) variability remains poorly understood due to limits of tide gauge records, low temporal resolution of tidal marsh records, and regional anomalies caused by dynamic ocean processes, notably multidecadal changes in Atlantic Meridional Overturning Circulation (AMOC). We examined SL and AMOC variability along the eastern United States over the last 2000 years, using a SL curve constructed from proxy SST records from Chesapeake Bay, and 20th century SL-sea-surface temperature (SST) relations derived from tide gauges and instrumental SST. The SL curve shows multidecadal-scale variability (20-30 yr) during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA), as well as the 20th century. During these SL oscillations, short-term rates ranged from 2 to 4 mm yr-1, roughly similar to those of the last few decades. These oscillations likely represent internal modes of climate variability related to AMOC variability and originating at high latitudes, although the exact mechanisms remain unclear. Results imply that dynamic ocean changes, in addition to thermosteric, glacio-eustatic or glacio-isostatic processes are an inherent part of SL variability in coastal regions, even during millennial-scale climate oscillations such as the MCA and LIA, and should be factored into efforts that use tide gauges and tidal marsh sediments to understand global sea-level rise.
R. E. Kopp, R. M. Horton et al. Probabilistic 21st and 22nd century sea-level projections at a global network of tide gauge sites. Earth's Future. Link to PDF
Sea-level rise due to both climate change and non-climatic factors threatens coastal settlements, infrastructure and ecosystems. Projections of mean global sea level (GSL) rise provide insufficient information to plan adaptive responses; local decisions require local projections that accommodate different risk tolerances and time frames and that can be linked to storm surge projections. Here we present a global set of local sea level (LSL) projections to inform decisions on timescales ranging from the coming decades through the 22nd century. We provide complete probability distributions, informed by a combination of expert community assessment, expert elicitation, and process modeling. Between the years 2000 and 2100, we project a (90% probability) GSL rise of 0.5–1.2 m under Representative Concentration Pathway (RCP) 8.5, 0.4–0.9 m under RCP 4.5, and 0.3–0.8 m under RCP 2.6. Site-to-site differences in LSL projections are due to varying non-climatic background uplift or subsidence, oceanographic effects, and spatially-variable responses of the geoid and the lithosphere to shrinking land ice. The Antarctic ice sheet (AIS) constitutes a growing share of variance in GSL and LSL projections. In the global average and at many locations, it is the dominant source of variance in late 21st century projections, though at some sites oceanographic processes contribute the largest share throughout the century. LSL rise dramatically reshapes flood risk, greatly increasing the expected number of ‘1-in-10’ and ‘1-in-100’ year events.Anny Cazenave and Gonéri Le Cozannet. Sea level rise and its coastal impacts. Earth's Future. http://onlinelibrary.wiley.com/doi/10.1002/2013EF000188/pdf
Global warming in response to accumulation of human-induced greenhouse gases inside the atmosphere has already caused several visible consequences, among them increase of the Earth's mean temperature and ocean heat content, melting of glaciers, and loss of ice from the Greenland and Antarctica ice sheets. Ocean warming and land ice melt in turn are causing sea level to rise. Sea level rise and its impacts on coastal zones have become a question of growing interest in the scientific community, as well as in the media and public. In this review paper, we summarize the most up-to-date knowledge about sea level rise and its causes, highlighting the regional variability that superimposes the global mean rise. We also present sea level projections for the 21st century under different warming scenarios. We next address the issue of the sea level rise impacts. We question whether there is already observational evidence of coastal impacts of sea level rise and highlight the fact that results differ from one location to another. This suggests that the response of coastal systems to sea level rise is highly dependent on local natural and human settings. We finally show that in spite of remaining uncertainties about future sea levels and related impacts, it becomes possible to provide preliminary assessment of regional impacts of sea level rise.
A number of recent papers have examined sea level data, both local tide gauge records and regional/global averages, to estimate not only how fast sea level is rising but how the rate has changed over time, i.e. its pattern of acceleration and deceleration. In addition, a number of claims of cyclic/quasi-periodic variations have been proposed. However, many of these papers contain technical problems which call their results into question. In particular, the issue of autocorrelation is often ignored, and even when it is addressed its impact has sometimes been misinterpreted. Autocorrelation does more than just affect the standard errors of regression analysis, it can also make the spectrum of a noise process distinctly “red” and therefore be highly suggestive of low-frequency periodic or pseudo-periodic behavior when none is present. If any analysis is applied which acts as a band-pass filter, it can further exaggerate the illusion of oscillatory behavior. These issues are highlighted in a small number of recent papers, in order to improve the quality of future work on this subject.Tal Ezer and Larry Atkinson. 2014. Accelerated flooding along the U. S. East Coast: On the impact of sea level rise, tides, storms, the Gulf Stream and NAO. in Earth' Future. DOI: 10.1002/2014EF000252.
Recent studies identified the U.S. East Coast north of Cape Hatteras as a “hotspot” for accelerated sea level rise (SLR), and the analysis presented here show that the area is also a “hotspot for accelerated flooding”. The duration of minor tidal flooding (defined as 0.3 m above MHHW) has accelerated in recent years for most coastal locations from the Gulf of Maine to Florida. The average increase in annual minor flooding duration was ~20 hours from the period until 1970 to 1971–1990, and ~50 hours from 1971–1990 to 1991–2013; spatial variations in acceleration of flooding resembles the spatial variations of acceleration in sea level. The increase in minor flooding can be predicted from SLR and tidal range, but the frequency of extreme storm-surge flooding events (0.9 m above MHHW) is less predictable, and affected by the North Atlantic Oscillations (NAO). The number of extreme storm surge events since 1960 oscillates with a period of ~15-year and interannual variations in the number of storms is anti-correlated with the NAO index. With higher seas, there are also more flooding events that are unrelated to storm surges. For example, it is demonstrated that week-long flooding events in Norfolk, VA, are often related to periods of decrease in the Florida Current transport. The results indicate that previously reported connections between decadal variations in the Gulf Stream and coastal sea level may also apply to short-term variations, so flood predictions may be improved if the Gulf Stream influence is considered.
William Sweet, Joseph Park, John Marra, Chris Zervas, Stephen Gill 2014. Sea Level Rise and Nuisance Flood Frequency Changes around the United States. in NOAA Technical Report NOS CO-OPS 073. LINK TO PDF
The National Oceanic and Atmospheric Administration (NOAA) water level (tide) gauges have been measuring water levels around the U.S. for over a century, providing clear evidence of sea level rise relative to land (SLRrel) around most of the continental United States and Hawaii. As SLRrel increases mean sea level (MSL), there is naturally an increase in tidal datum elevations, which are typically used to delineate inundation thresholds. Direct consequences of rising sea level against fixed elevations such as today’s built infrastructure also include increased inundation during extreme events both spatially and temporally. Not only are extreme flooding events reaching higher grounds and covering larger areas due to SLRrel, the frequency and duration of these extreme flood events are increasing.
Another consequence of SLRrel is the increase in lesser extremes such as occasional minor coastal flooding experienced during high tide. These events are becoming more noticeable and widespread along many U.S. coastal regions and are today becoming more of a nuisance. As sea levels continue to rise and with an anticipated acceleration in the rate of rise from ocean warming and land-ice melt, concern exists as to when more substantive impacts from tidal flooding of greater frequency and duration will regularly occur. Information quantifying these occurrences to inform mitigation and adaptation efforts and decision makers is not widely available.
In this report, we show that water level exceedances above the elevation threshold for “minor” coastal flooding (nuisance level) impacts established locally by the National Weather Service (NWS) have been increasing in time. More importantly, we document that event frequencies are accelerating at many U.S. East and Gulf Coast gauges, and many other locations will soon follow regardless of whether there is an acceleration of SLRrel. Lastly, we show a regional pattern of
increasingly greater event-rate acceleration as the height between MSL and a location’s nuisance flood threshold elevation decreases.
Impacts from recurrent coastal flooding include overwhelmed stormwater drainage capacity, frequent road closures, and general deterioration and corrosion of infrastructure not designed to withstand frequent inundation or salt-water exposure. From this, we conclude that there is a time horizon, largely dependent upon the local rate of SLRrel, when critical elevation thresholds for various public/private/commercial serving systems will become increasingly compromised by tidal flooding. This concept of a non-linear impact trajectory needs to recognized, as it is critical for coastal planning to prevent degradation to society-serving systems at risk from SLRrel. The goal of this report is to heighten awareness of a growing problem of more frequent nuisance coastal flooding respective to a community’s living memory and to encourage resiliency efforts in response to impacts from SLRrel.Donald R Cahoon. 2014. Estimating Relative Sea-Level Rise and Submergence Potential at a Coastal Wetland. Estuaries and Coasts, September 2014. 10.1007/s12237-014-9872-8
Abstract - A tide gauge records a combined signal of the vertical change (positive or negative) in the level of both the sea and the land to which the gauge is affixed; or relative sea-level change, which is typically referred to as relative sea-level rise (RSLR). Complicating this situation, coastal wetlands exhibit dynamic surface elevation change (both positive and negative), as revealed by surface elevation table (SET) measurements, that is not recorded at tide gauges. Because the usefulness of RSLR is in the ability to tie the change in sea level to the local topography, it is important that RSLR be calculated at a wetland that reflects these local dynamic surface elevation changes in order to better estimate wetland submergence potential. A rationale is described for calculating wetland RSLR (RSLRwet) by subtracting the SET wetland elevation change from the tide gauge RSLR. The calculation is possible because the SET and tide gauge independently measure vertical land motion in different portions of the substrate. For 89 wetlands where RSLRwet was evaluated, wetland elevation change differed significantly from zero for 80 % of them, indicating that RSLRwet at these wetlands differed from the local tide gauge RSLR. When compared to tide gauge RSLR, about 39 % of wetlands experienced an elevation rate surplus and 58 % an elevation rate deficit (i.e., sea level becoming lower and higher, respectively, relative to the wetland surface). These proportions were consistent across saltmarsh, mangrove, and freshwater wetland types. Comparison of wetland elevation change and RSLR is confounded by high levels of temporal and spatial variability, and would be improved by co-locating tide gauge and SET stations near each other and obtaining long-term records for both.Baruch Fischhoff and Alex L. Davis, 2014, Communicating scientific uncertainty. PNAS. vol. 111 no. Supplement 4, 13664-13671. DOI10.1073/pnas.1317504111 Link
All science has uncertainty. Unless that uncertainty is communicated effectively, decision makers may put too much or too little faith in it. The information that needs to be communicated depends on the decisions that people face. Are they (i) looking for a signal (e.g., whether to evacuate before a hurricane), (ii) choosing among fixed options (e.g., which medical treatment is best), or (iii) learning to create options (e.g., how to regulate nanotechnology)? We examine these three classes of decisions in terms of how to characterize, assess, and convey the uncertainties relevant to each. We then offer a protocol for summarizing the many possible sources of uncertainty in standard terms, designed to impose a minimal burden on scientists, while gradually educating those whose decisions depend on their work. Its goals are better decisions, better science, and better support for science.G. Jordà. 2014. Detection time for global and regional sea level trends and accelerations. Journal of Geophysical Research: Oceans DOI 10.1002/2014JC010005
Many studies analyse trends on sea level data with the underlying purpose of finding indications of a long-term change that could be interpreted as the signature of anthropogenic climate change. The identification of a long-term trend is a signal-to-noise problem where the natural variability (the ‘noise’) can mask the long-term trend (the ‘signal’). The signal-to-noise ratio depends on the magnitude of the long-term trend, on the magnitude of the natural variability and on the length of the record, as the climate noise is larger when averaged over short timescales and becomes smaller over longer averaging periods. In this paper we evaluate the time required to detect centennial sea level linear trends and accelerations at global and regional scales. Using model results and tide gauge observations we find that the averaged detection time for a centennial linear trend is 87.9, 76.0, 59.3, 40.3 and 25.2 years for trends of 0.5, 1.0, 2.0, 5.0 and 10.0 mm/yr, respectively. However, in regions with large decadal variations like the Gulf Stream or the Circumpolar current these values can increase up to a 50%. The spatial pattern of the detection time for sea level accelerations is almost identical. The main difference is that the length of the records has to be about 40-60 years longer to detect an acceleration than to detect a linear trend leading to an equivalent change after 100 years. Finally we have used a new sea level reconstruction which provides a more accurate representation of interannual variability for the last century in order to estimate the detection time for global mean sea level trends and accelerations. Our results suggest that the signature of natural variability in a 30 year global mean sea level record would be less than 1 mm/yr. Therefore, at least 2.2 mm/yr of the recent sea level trend estimated by altimetry cannot be attributed to natural multidecadal variability.A Longa, N Barlow and others. . 2014. Contrasting records of sea-level change in the eastern and western North Atlantic during the last 300 years.Earth and Planetary Science Letters
Volume 388, 15 February 2014, Pages 110–122.
- Sea-level data from NW European tide gauges and salt marshes agree since AD 1700.•
- Since c. AD 1700 sea-level rose in southern Britain by 0.30 m at c. .•
- US east coast 20th century sea-level trends are higher than those from NW Europe.•
- Semi-empirical models may over-estimate future sea-level rise if tuned to one site.
Abstract - We present a new 300-year sea-level reconstruction from a salt marsh on the Isle of Wight (central English Channel, UK) that we compare to other salt-marsh and long tide-gauge records to examine spatial and temporal variability in sea-level change in the North Atlantic. Our new reconstruction identifies an overall rise in relative sea level (RSL) of c. 0.30 m since the start of the eighteenth century at a rate of . Error-in-variables changepoint analysis indicates that there is no statistically significant deviation from a constant rate within the dataset. The reconstruction is broadly comparable to other tide-gauge and salt-marsh records from the European Atlantic, demonstrating coherence in sea level in this region over the last 150–300 years. In contrast, we identify significant differences in the rate and timing of RSL with records from the east coast of North America. The absence of a strong late 19th/early 20th century RSL acceleration contrasts with that recorded in salt marsh sediments along the eastern USA coastline, in particular in a well-dated and precise sea-level reconstruction from North Carolina. This suggests that this part of the North Carolina sea level record represents a regionally specific sea level acceleration. This is significant because the North Carolina record has been used as if it were globally representative within semi-empirical parameterisations of past and future sea-level change. We conclude that regional-scale differences of sea-level change highlight the value of using several, regionally representative RSL records when calibrating and testing semi-empirical models of sea level against palaeo-records. This is because by using records that potentially over-estimate sea-level rise in the past such models risk over-estimating sea-level rise in the future.Robert E. Kopp, Benjamin P. Horton, Andrew C. Kemp and Claudia Tebaldi. 2014. Past and future sea-level rise along the coast of North Carolina, United States. arXiv preprint arXiv:1410.8369,, 2014 Link
Abstract - Focusing on factors that cause relative sea-level (RSL) rise to differ from the global mean, we evaluate RSL trajectories for North Carolina, United States, in the context of tide gauge and geological sea-level proxy records spanning the last 11,000 years. RSL rise was fastest ( 7 mm/yr) during the early Holocene and decreased over time. During the Common Era before the 19th century, RSL rise ( 0.7 to 1.1 mm/yr) was driven primarily by glacio-isostatic adjustment, dampened by tectonic uplift along the Cape Fear Arch. Ocean/atmosphere dynamics caused centennial variability of up to 0.6 mm/yr around the long-term rate. It is extremely likely (probability P = 0:95) that 20th century RSL rise at Sand Point, NC, (2.8 0.5 mm/yr) was faster than during any other century in 2; 900 years. Projections based on a fusion of process models, statistical models, expert elicitation and expert assessment indicate that RSL at Wilmington, NC, is very likely (P = 0:90) to rise by 42–132 cm between 2000 and 2100 under the high-emissions RCP 8.5 pathway. Under all emission pathways, 21st century RSL rise is very likely (P > 0:90) to be faster than during the 20th century. Because sea level responds slowly to climate forcing, RSL rise in North Carolina to 2050 varies by <6 cm between pathways. Due to RSL rise, under RCP 8.5, the current ‘1-in-100 year’ flood is expected at Wilmington in 30 of the 50 years between 2050-2100.
Philip L. Woodworth, Miguel Á. Morales Maqueda et al., 2014. Mean Sea Level Variability along the Northeast American Atlantic Coast and the Roles of the Wind and the Overturning Circulation. Journal of Geophysical Research: Oceans
The variability in mean sea level (MSL) during 1950-2009 along the northeast American
Atlantic coast north of Cape Hatteras has been studied, using data from tide gauges and satellite altimetry and information from the Liverpool/Hadley Centre (LHC) ocean model, thereby providing new insights into the spatial and temporal scales of the variability. Although a relationship between sea level and the overturning circulation can be identified (an increase of approximately 1.5 cm in MSL for a decrease of 1 Sv in overturning transport), it is the effect of the near-shore wind forcing on the shelf that is found to dominate the interannual sea level variability. In particular, winds are found to be capable of producing low-frequency changes in MSL (‘accelerations’) in a narrow coastal band, comparable to those observed by the tide gauges. Evidence is presented supporting the idea of a ‘common mode’ of spatially-coherent low-frequency MSL variability, both to the north and south of Cape Hatteras and throughout the northwest Atlantic, which is associated with large spatial-scale density changes from year to year.
J. S. Kenigson and 1 W. Han. 2014. Detecting and Understanding the Accelerated Sea Level Rise along the East Coast of the United States during Recent Decades. Journal of Geophysical Research: Oceans, DOI 10.1002/2014JC010305. Link
A \hotspot" of accelerated sea level rise has recently been detected between Cape Hatteras and Cape Cod. The acceleration in the longterm trend, however, is di cult to isolate from transient acceleration due to variability, particularly the 60-year cycle associated with the Atlantic Multidecadal Oscillation (AMO). The Empirical Mode Decomposition (EMD) and Ensemble EMD (EEMD) methods have been used to isolate oscillations and provide robust acceleration estimates for the trend. Yet the reliability of these methods in detecting accelerated sea level rise, particularly given the limited lengths of tide gauge records, has not been fully tested. Here, the EMD and EEMD methods are applied to both tide gauge observations and synthetic sea level time series constructed as a sum of oscillations extracted from tide gauge records and trends with prescribed acceleration rates. The successively truncated synthetic and observed data are analyzed with (E)EMD, and estimates of the acceleration error based on the record length are produced. Generally, EEMD provides more stable acceleration estimates than EMD, and the error decreases as the record length increases, although not
monotonically. Records exceeding two multidecadal oscillation periods in length provide superior estimates over shorter records. In addition, the AMO may have contributed signi cantly to the rapid acceleration detected in the hotspot during recent decades. These ndings have important implications for improved detection of regional sea level acceleration in a warming climate.
Lyle M. Varnell. 2014. Shoreline Energy and Sea Level Dynamics in Lower Chesapeake Bay: History and Patterns, Estuaries and Coasts March 2014, Volume 37, Issue 2, pp 508-523 Link
A long-term (1948–2010) shoreward energy history of upper tidal shorelines in lower Chesapeake Bay was developed using a simple calculation of kinetic energy from corresponding wind and tide data. These data were primarily used to determine the likelihood of shoreline energy increases coincident with local sea level rise. Total annual shoreward energy ranged from 620 kJ/m of shoreline in 1950 to 17,785 kJ/m of shoreline in 2009. No clear linear trends are apparent, but mean annual energy shows an increase from 2,732 kJ/m before 1982 to 6,414 kJ/m since then. This increase in mean energy was accompanied by more numerous spikes of comparatively higher annual energy. Shoreward energy delivered to lower Chesapeake Bay’s upper tidal shorelines was enabled by an increasing amount of time per year that tidal height exceeds mean high water, accompanied by increasing heights of tidal anomalies. An index termed the Hydrologic Burden was developed that incorporates the combination of time and tidal height that demonstrates this increasing trend. Although opportunities for greater shoreward energy increased as the Hydrologic Burden increased, and even though there is evidence that greater energy was delivered to the shorelines during the latter time series, energy per hour delivery was shown not to have increased, and may have decreased, due to a steady reduction in average wind speed in lower Chesapeake Bay since the mid-1980s. Energy delivery in lower Chesapeake Bay was primarily from the northeast, and energy delivery over the time series is shown to organize symmetrically around a point between the northeast and north–northeast directions. This is evidence of a self-organizational phenomenon that transcends changes in local wind and tide dynamics.
James E. Neumann & Kerry Emanuel & Sai Ravela & Lindsay Ludwig & Paul Kirshen & Kirk Bosma & Jeremy Martinich. 2014. Joint effects of storm surge and sea-level rise on US Coasts: new economic estimates of impacts, adaptation, and benefits of mitigation policy. Climatic Change DOI 10.1007/s10584-014-1304-z . LINK
Abstract Recent literature, the US Global Change Research Program’s National Climate
Assessment, and recent events, such as Hurricane Sandy, highlight the need to take better
account of both storm surge and sea-level rise (SLR) in assessing coastal risks of climate
change. This study combines three models—a tropical cyclone simulation model; a storm surge model; and a model for economic impact and adaptation—to estimate the joint effects of storm surge and SLR for the US coast through 2100. The model is tested using multiple SLR scenarios, including those incorporating estimates of dynamic ice-sheet melting, two global greenhouse gas (GHG) mitigation policy scenarios, and multiple general circulation model climate sensitivities. The results illustrate that a large area of coastal land and property is at risk of damage from storm surge today; that land area and economic value at risk expands over time as seas rise and as storms become more intense; that adaptation is a cost-effective response to this risk, but residual impacts remain after adaptation measures are in place; that incorporating site-specific episodic storm surge increases national damage estimates by a factor of two relative to SLR-only estimates, with greater impact on the East and Gulf coasts; and that mitigation of GHGs contributes to significant lessening of damages. For a mid-range climate-sensitivity scenario that incorporates dynamic ice sheet melting, the approach yields national estimates of the impacts of storm surge and SLR of $990 billion through 2100 (net of adaptation, cumulative undiscounted 2005$); GHG mitigation policy reduces the impacts of the mid-range climate-sensitivity estimates by $84 to $100 billion.
William Sweet and Joseph Park. 2014 From the extreme to the mean: Acceleration and tipping
points of coastal inundation from sea level rise. Earth's Future. doi:10.1002/2014EF000272. LINK
Relative sea level rise (RSLR) has driven large increases in annual water level exceedances (duration and frequency) above minor (nuisance level) coastal flooding elevation thresholds established by the National Weather Service (NWS) at U.S. tide gauges over the last half-century. For threshold levels below 0.5m above high tide, the rates of annual exceedances are accelerating along the U.S. East and Gulf Coasts, primarily from evolution of tidal water level distributions to higher elevations impinging on the flood threshold. These accelerations are quantified in terms of the local RSLR rate and tidal range through multiple regression analysis. Along the U.S. West Coast, annual exceedance rates are linearly increasing, complicated by sharp punctuations in RSLR anomalies during El Niño Southern Oscillation (ENSO) phases, and we account for annual exceedance variability along the U.S. West and East Coasts from ENSO forcing. Projections of annual exceedances above local NWS nuisance levels at U.S. tide gauges are estimated by shifting probability estimates of daily maximum water levels over a contemporary 5-year period following probabilistic RSLR projections of Kopp et al. (2014) for representative concentration pathways (RCP) 2.6, 4.5, and 8.5. We suggest a tipping point for coastal inundation (30 days/per year with a threshold exceedance) based on the evolution of exceedance probabilities. Under forcing associated with the local-median projections of RSLR, the majority of locations surpass the tipping point over the next several decades regardless of specific RCP.
S. Higginson, K.R. Thompson, P.L. Woodworth, and C.W. Hughes. 2015. The tilt of mean sea level along the east coast of North America. GRL. DOI: 10.1002/2015GL063186
Abstract - The tilt of mean sea level along the North American east coast has been a subject of debate for many decades. Improvements in geoid and ocean circulation models, and GPS positioning of tide gauge benchmarks, provide an opportunity to produce new tilt estimates. Tilts estimated using tide gauge measurements referenced to high-resolution geoid models (the geodetic approach) and ocean circulation models (the ocean approach) are compared. The geodetic estimates are broadly similar, with tilts downwards to the north through the Florida Straits and at Cape Hatteras. Estimates from the ocean approach show good agreement with the geodetic estimates, indicating a convergence of the two approaches and resolving the long standing debate as to the sign of the tilt. These tilts differ from those used by Yin and Goddard  to support a link between changing ocean circulation and coastal sea level rise.
Tal Ezer. 2015 Detecting changes in the transport of the Gulf Stream and the Atlantic
overturning circulation from coastal sea level data: The extreme decline in 2009–2010 and estimated variations for 1935–2012 . Global and Planetary Change. 129 (2015) 23–36. LINK to PDF
Abstract - Recent studies reported weakening in the Atlantic Meridional Overturning Circulation (AMOC) and in the Gulf Stream (GS), using records of about a decade (RAPID project) or two (altimeter data). Coastal sea level records are much longer, so the possibility of detecting climatic changes in ocean circulation from sea level data is intriguing and thus been examined here. First, it is shown that variations in the AMOC transport from the RAPID project since 2004 are consistent with the flow between Bermuda and the U. S. coast derived from the Oleander measurements and from sea level difference (SLDIF). Despite apparent disagreement between recent studies on the ability of data to detect weakening in the GS flow, estimated transport changes from3 different independent data sources agree quite well with each other on the extreme decline in transport in 2009–2010. Due to eddies and meandering, the flow representing the GS part of the Oleander line is not correlated with AMOC or with the Florida Current, only the flow across the entire Oleander line from the U.S. coast to Bermuda is correlated with climatic transport changes. Second, Empirical Mode Decomposition (EMD) analysis shows that SLDIF can detect (with lag) the portion of the variations in theAMOC transport that are associatedwith the Florida Current and thewind-driven Ekman transport (SLDIF-transport correlations of ~0.7–0.9). The SLDIF has thus been used to estimate variations in transport since 1935 and compared with AMOC obtained from reanalysis data. The significant weakening in AMOC after ~2000 (~4.5 Sv per decade) is comparable to weakening seen in the 1960s to early 1970s. Both periods of weakening AMOC, in the 1960s and 2000s, are characterized by faster than normal sea level rise along the northeastern U.S. coast, so monitoring changes in AMOC has practical implications for coastal protection.
Stefan Rahmstorf, Jason Box, Georg Feuiner, Michael Mann, Alexander Robinson, Scott Rutherford and Erik Schaffernicht. 2015. Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation. Nature Climate Change. doi:10.1038/nclimate2554 LINK to PDF
Possible changes in Atlantic meridional overturning circulation (AMOC) provide a key source of uncertainty regarding future climate change. Maps of temperature trends over the twentieth century show a conspicuous region of cooling in the northern Atlantic. Here we present multiple lines of evidence suggesting that this cooling may be due to a reduction in the AMOC over the twentieth century and particularly after 1970. Since 1990 the AMOC seems to have partly recovered. This time evolution is consistently suggested by an AMOC index based on sea surface temperatures, by the hemispheric temperature difference, by coral-based proxies and by oceanic measurements. We discuss a possible contribution of the melting of the Greenland Ice Sheet to the slowdown. Using a multi-proxy temperature reconstruction for the AMOC index suggests that the AMOC weakness after 1975 is an unprecedented event in the past millennium (p > 0.99). Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC.
Keith J. Roberts1and Brian A. Colle. 2015. A Regression-based Approach for Cool-Season Storm Surge Predictions along the New York/New Jersey Coast. Journal of Applied Meteorology and Climatology 2015 ; e-View doi: http://dx.doi.org/10.1175/JAMC-D-14-0314.1
A multi-linear regression (MLR) approach is developed to predict 3-hourly storm surge during the cool season months (Oct. 1-March 31) between 1979-2012 using two different atmospheric reanalysis datasets and water level observations at three stations along the New York/New Jersey coast (Atlantic City, New Jersey, The Battery in New York City, and Montauk Point, New York). The predictors of the MLR are specified to represent prolonged surface wind stress and a sea-level pressure minimum for a boxed region near each station. The regression underpredicts relatively large (≥ 95th percentile) storm maximum surge heights by 6.0-38.0%. The bias-correction technique reduces the average mean absolute error by 10-15% at the various stations for storm maximum surge predictions. Using the same forecasted surface winds and pressures from the North American Mesoscale (NAM) model between October-March 2010 to 2014, raw and bias-corrected surge predictions at The Battery are compared to raw output from a numerical hydrodynamic model’s (SIT-NYHOPS) predictions. The accuracy of surge predictions between the SIT-NYHOPS and bias corrected MLR model at The Battery are similar for predictions that meet or exceed the 95th percentile of storm maximum surge heights.
Hans Visser1,Sönke Dangendorf, and Arthur C. Petersen. 2015. A review of trend models applied to sea level data with reference to the “acceleration-deceleration debate”. Journal of Geophysical Research: Oceans. J. Geophys. Res. Oceans, http://dx.doi.org/10.1002/2015JC010716 DO - 10.1002/2015JC010716
Abstract - Global sea levels have been rising through the past century and are projected to rise at an accelerated rate throughout the 21st century. This has motivated a number of authors to search for already existing accelerations in observations, which would be, if present, vital for coastal protection planning purposes. No scientific consensus has been reached yet as to how a possible acceleration could be separated from intrinsic climate variability in sea level records. This has led to an intensive debate on its existence and, if absent, also on the general validity of current future projections. Here we shed light on the controversial discussion from a methodological point of view. To do so we provide a comprehensive review of trend methods used in the community so far. This resulted in an overview of 30 methods, each having its individual mathematical formulation, flexibilities and characteristics. We illustrate that varying trend approaches may lead to contradictory acceleration–deceleration inferences. As for statistics-oriented trend methods we argue that checks on model assumptions and model selection techniques yield a way out. However, since these selection methods all have implicit assumptions, we show that good modeling practices are of importance too. We conclude at this point that (i) several differently characterized methods should be applied and discussed simultaneously, (ii) uncertainties should be taken into account to prevent biased or wrong conclusions, and (iii) removing internally generated climate variability by incorporating atmospheric or oceanographic information helps to uncover externally forced climate change signals. This article is protected by copyright.
Paul B. Goddard, Jianjun Yin, Stephen M. Griffies & Shaoqing Zhang. 2015. An extreme event of sea-level rise along the Northeast coast of North America in 2009–2010. Nature Communications 6, Article number: 6346 doi:10.1038/ncomms7346
The coastal sea levels along the Northeast Coast of North America show significant year-to-year fluctuations in a general upward trend. The analysis of long-term tide gauge records identified an extreme sea-level rise (SLR) event during 2009–10. Within this 2-year period, the coastal sea level north of New York City jumped by 128 mm. This magnitude of interannual SLR is unprecedented (a 1-in-850 year event) during the entire history of the tide gauge records. Here we show that this extreme SLR event is a combined effect of two factors: an observed 30% downturn of the Atlantic meridional overturning circulation during 2009–10, and a significant negative North Atlantic Oscillation index. The extreme nature of the 2009–10 SLR event suggests that such a significant downturn of the Atlantic overturning circulation is very unusual. During the twenty-first century, climate models project an increase in magnitude and frequency of extreme interannual SLR events along this densely populated coast.
B.D. Hamlington, R.R. Leben, K.-Y. Kim, R.S. Nerem, L.P. Atkinson, P.R. Thompson. 2015. The Effect of the El Niño-Southern Oscillation on United States Regional and Coastal Sea Level. Journal of Geophysical Research: Oceans DOI 10.1002/2014JC010602
Although much of the focus on future sea level rise concerns the long-term trend
associated with anthropogenic warming, on shorter timescales, internal climate variability can contribute significantly to regional sea level. Such sea level variability should be taken into consideration when planning efforts to mitigate the effects of future sea level change. In this study, we quantify the contribution to regional sea level of the El Niño- Southern Oscillation (ENSO). Through cyclostationary empirical orthogonal function analysis (CSEOF) of the long reconstructed sea level dataset and of a set of United States tide gauges, two global modes dominated by Pacific Ocean variability are identified and related to ENSO and, by extension, the Pacific Decadal Oscillation. By estimating the combined contribution of these two modes to regional sea level, we find that ENSO can contribute significantly on short time scales, with contributions of up to 20 cm along the west coast of the U.S. The CSEOF decomposition of the long tide gauge records around the U.S. highlights the influence of ENSO on the U.S. east coast. Tandem analyses of both the reconstructed and tide gauge records also examine the utility of the sea level reconstructions for near-coast studies.
Gerard D. McCarthy, Ivan D. Haigh, Joël J.-M. Hirschi, Jeremy P. Grist and David A. Smeed. 2015. Ocean impact on decadal Atlantic climate variability revealed by sea-level observations. Nature 521, 508–510 (28 May 2015) doi:10.1038/nature14491.
Decadal variability is a notable feature of the Atlantic Ocean and the climate of the regions it influences. Prominently, this is manifested in the Atlantic Multidecadal Oscillation (AMO) in sea surface temperatures. Positive (negative) phases of the AMO coincide with warmer (colder) North Atlantic sea surface temperatures. The AMO is linked with decadal climate fluctuations, such as Indian and Sahel rainfall, European summer precipitation, Atlantic hurricanes3 and variations in global temperatures. It is widely believed that ocean circulation drives the phase changes of the AMO by controlling ocean heat content. However, there are no direct observations of ocean circulation of sufficient length to support this, leading to questions about whether the AMO is controlled from another source. Here we provide observational evidence of the widely hypothesized link between ocean circulation and the AMO. We take a new approach, using sea level along the east coast of the United States to estimate ocean circulation on decadal timescales. We show that ocean circulation responds to the first mode of Atlantic atmospheric forcing, the North Atlantic Oscillation, through circulation changes between the subtropical and subpolar gyres—the intergyre region7. These circulation changes affect the decadal evolution of North Atlantic heat content and, consequently, the phases of the AMO. The Atlantic overturning circulation is declining8 and the AMO is moving to a negative phase. This may offer a brief respite from the persistent rise of global temperatures4, but in the coupled system we describe, there are compensating effects. In this case, the negative AMO is associated with a continued acceleration of sea-level rise along the northeast coast of the United States
Alan Blumberg, Nickitas Georgas, Larry Yin, Thomas Herrington, and Philip Orton. 2015.
Street Scale Modeling of Storm Surge Inundation along the New Jersey Hudson River Waterfront. Journal of Atmospheric and Oceanic Technology 2015 ; e-View
A new, high-resolution, hydrodynamic model that encompasses the urban coastal waters of New Jersey along the Hudson River waterfront opposite New York City has been developed and validated for simulating inundation during Hurricane Sandy. A 3.1 m resolution square model grid combined with high-resolution LiDAR elevation dataset permit a street by street focus to inundation modeling. The waterfront inundation model is a triple nested sECOM model application; sECOM is a successor model to the Princeton Ocean Model family of models. Robust flooding and drying of land in the model physics provides for the dynamic prediction of flood elevations and velocities across land features during inundation events. The inundation model was forced by water levels from the extensively validated NYHOPS hindcast of that hurricane.
Validation against 56 water marks and 16 edgemarks provided via the USGS and through an extensive crowd sourcing effort consisting of photographs, videos and personal stories shows that the model is capable of computing overland water elevations quite accurately throughout the entire surge event. The correlation coefficient (R2) between the water mark observations and the model results is 0.92. The standard deviation of the residual error is 0.07 m. Comparisons to the 16 flood edgemarks suggest that the model was able to reproduce flood extent to within 20 m. Because the model was able to capture the spatial and temporal variation of water levels in the region observed during Hurricane Sandy, it was used to identify the flood pathways and suggest where flood preventing interventions could be built.
John D. Boon and Molly Mitchell. 2015. Nonlinear Change in Sea Level Observed at North American Tide Stations. Journal of Coastal Research. Link to PDF
Abstract - The rate at which coastal sea level is expected to rise or fall is of considerable interest to coastal residents and managers who view changes on the time scale of a 30-year mortgage. Analysis of historical records at North American tide stations provides evidence of recent nonlinear sea-level change at this scale using relative mean sea-level (RMSL) observations. RMSL tracks local inundation risk directly without the need to correct an accepted worldwide geocentric measure—e.g., global mean sea-level rise—with locally estimated vertical rate adjustments. Published RMSL linear trends provide essential information but are routinely compared between tide stations with widely varying record lengths, thereby obfuscating nonlinear change (acceleration or deceleration) over a specific period of time. Here monthly averaged RMSL data from 45 U.S. tide stations and one Canadian tide station are analyzed from 1969 through 2014, extending a definitive period of acceleration previously noted along the U.S. NE Coast. Using a Bayesian approach to determine the joint probability of paired regression parameters for RMSL quadratic trends, probabilities for forward projections to the year 2050 based on these trends suggest continued sea-level rise will be aided by acceleration presently on the order of 0.1 to 0.2 mm/y2 in the U.S. NE and Gulf Coast regions. Deceleration ranging from 0.1 to 0.4 mm/y2 is likely to reinforce falling sea levels at specific locations on the U.S. West Coast in the near term.
Benjamin DeJong et al. 2015. Pleistocene relative sea levels in the Chesapeake Bay
region and their implications for the next century. GSA Today, v. 25, no. 8, doi: 10.1130/GSATG223A.1.Link to PDF
Today, relative sea-level rise (3.4 mm/yr) is faster in the Chesapeake Bay region than any other location on the Atlantic coast of North America, and twice the global average eustatic rate (1.7 mm/yr). Dated interglacial deposits suggest that relative sea levels in the Chesapeake Bay region deviate from global trends over a range of timescales. Glacio-isostatic adjustment of the land surface from loading and unloading of continental ice is likely responsible for these deviations, but our understanding of the scale and timeframe over which isostatic response operates in this region remains incomplete because dated sea-level proxies are mostly limited to the Holocene and to deposits 80 ka or older.
To better understand glacio-isostatic control over past and present relative sea level, we applied a suite of dating methods to the stratigraphy of the Blackwater National Wildlife Refuge, one of the most rapidly subsiding and lowest-elevation surfaces bordering Chesapeake Bay. Data indicate that the region was submerged at least for portions of marine isotope stage (MIS) 3 (ca. 60–30 ka), although multiple proxies suggest that global sea level was 40–80 m lower than present. Today MIS 3 deposits are above sea level because they were raised by the Last Glacial Maximum forebulge, but decay of that same forebulge is causing ongoing subsidence. These results suggest that glacio-isostasy controlled relative sea level in the mid-Atlantic region for tens of thousands of years following retreat of the Laurentide Ice Sheet and continues to influence relative sea level in the region. Thus, isostatically driven subsidence of the Chesapeake Bay region will continue for millennia, exacerbating the effects of global sea-level rise and impacting the region’s large population centers and valuable coastal natural resources.
Christopher M. Little et al. 2015. Joint projections of US East Coast sea level and storm surge.Nature Climate Change doi:10.1038/nclimate2801 Link to PDF
Future coastal flood risk will be strongly influenced by sea-level rise (SLR) and changes in the frequency and intensity of tropical cyclones. These two factors are generally considered independently. Here, we assess twenty-first century changes in the coastal hazard for the US East Coast using a flood index (FI) that accounts for changes in flood duration and magnitude driven by SLR and changes in power dissipation index (PDI, an integrated measure of tropical cyclone intensity, frequency and duration). Sea-level rise and PDI are derived from representative concentration pathway (RCP) simulations of 15 atmosphere–ocean general circulation models (AOGCMs). By 2080–2099, projected changes in the FI relative to 1986–2005 are substantial and positively skewed: a 10th–90th percentile range 4–75 times higher for RCP 2.6 and 35–350 times higher for RCP 8.5. High-end FI projections are driven by three AOGCMs that project the largest increases in SLR, PDI and upper ocean temperatures. Changes in PDI are particularly influential if their intra-model correlation with SLR is included, increasing the RCP 8.5 90th percentile FI by a further 25%. Sea-level rise from other, possibly correlated, climate processes (for example, ice sheet and glacier mass changes) will further increase coastal flood risk and should be accounted for in comprehensive assessments.
J. Park and W. Sweet. 2015. Accelerated sea level rise and Florida Current transport. Ocean Sci., 11, 607–615, 2015 www.ocean-sci.net/11/607/2015/ doi:10.5194/os-11-607-2015. LINK
Abstract. The Florida Current is the headwater of the Gulf Stream and is a component of the North Atlantic western boundary current from which a geostrophic balance between sea surface height and mass transport directly influence coastal sea levels along the Florida Straits. A linear regression of daily Florida Current transport estimates does not find a significant change in transport over the last decade; however, a nonlinear trend extracted from empirical mode decomposition (EMD) suggests a 3 Sv decline in mean transport. This decline is consistent with observed tide gauge records in Florida Bay and the straits exhibiting an acceleration of mean sea level (MSL) rise over the decade. It is not known whether this recent change represents natural variability or the onset of the anticipated secular decline in Atlantic meridional overturning circulation (AMOC); nonetheless, such changes have direct impacts on the sensitive ecological systems of the Everglades as well as the climate of western Europe and eastern North America.Benjamin P. Horton et al. 2015. Science Needs for Sea-Level Adaptation Planning:
Comparisons among Three U.S. Atlantic Coastal Regions. Coastal Management, 43:555–574, DOI: 10.1080/08920753.2015.1075282 LINK
To identify priority information needs for sea-level rise planning, we conducted
workshops in Florida, North Carolina, and Massachusetts in the summer of 2012.
Attendees represented professionals from five stakeholder groups: federal and state
governments, local governments, universities, businesses, and nongovernmental
organizations. Over 100 people attended and 96 participated in breakout groups. Text
analysis was used to organize and extract most frequently occurring content from 16
total breakout groups. The most frequent key words/phrases were identified among
priority topics within five themes: analytic tools, communications, land use, ecosystem
management, and economics. Diverse technical and communication tools were
identified to help effectively plan for change. In many communities, planning has not
formally begun. Attendees sought advanced prediction tools yet simple messaging for
decision-makers facing politically challenging planning questions. High frequency key words/phrases involved fine spatial scales and temporal scales of less than 50 years. Many needs involved communications and the phrase “simple messaging” appeared with the highest frequency. There was some evidence of geographic variation among regions. North Carolina breakout groups had a higher frequency of key words/phrases involving land use. The results reflect challenges and tractable opportunities for planning beyond current, geophysically brief, time scales (e.g., election cycles and mortgage periods).
Karegar, M.A., T. H. Dixon, S. E. Engelhart. 2015. Subsidence along the Atlantic Coast of North America: Insights from GPS and late Holocene relative sea level data. GRL LINK
Abstract - The Atlantic Coast of North America is increasingly affected by flooding associated with tropical and extratropical storms, exacerbated by the combined effects of accelerated sea-level rise and land subsidence. The region includes the collapsing forebulge of the Laurentide Ice Sheet. High-quality records of late Holocene relative sea-level (RSL) rise are now available, allowing separation of long-term glacial isostatic adjustment-induced displacement from modern vertical displacement measured by GPS. We compare geological records of late Holocene RSL to present-day vertical rates from GPS. For many coastal areas there is no significant difference between these independent data. Exceptions occur in areas of recent excessive groundwater extraction, between Virginia (38°N) and South Carolina (32.5°N). The present-day subsidence rates in these areas are approximately double the long-term geologic rates, which has important implications for flood mitigation. Tide gauge records, therefore, should be used with caution for studying sea-level rise in this region.
Shimon Wdowinskia, Ronald Braya, Ben P. Kirtmana, Zhaohua Wub. 2016. Increasing flooding hazard in coastal communities due to rising sea level: Case study of Miami Beach, Florida. Ocean and Coastal Management. Volume 126, June 2016, Pages 1- 8. http://dx.doi.org/10.1016/j.ocecoaman.2016.03.002
Sea level rise (SLR) imposes an increasing flooding hazard on low-lying coastal communities due to higher exposure to high-tide conditions and storm surge. Additional coastal flooding hazard arises due to reduced effectiveness of gravity-based drainage systems to drain rainwater during heavy rain events. Over the past decade, several coastal communities along the US Atlantic coast have experienced an increasing rate of flooding events. In this study, we focus on the increasing flooding hazard in Miami Beach, Florida, which has caused severe property damage and significant disruptions to daily life. We evaluate the flooding frequency and its causes by analyzing tide and rain gauge records, media reports, insurance claims, and photo records from Miami Beach acquired during 1998–2013. Our analysis indicates that significant changes in flooding frequency occurred after 2006, in which rain-induced events increased by 33% and tide-induced events increased by more than 400%. We also analyzed tide gauge records from Southeast Florida and detected a decadal-scale accelerating rates of SLR. The average pre-2006 rate is 3 ± 2 mm/yr, similar to the global long-term rate of SLR, whereas after 2006 the average rate of SLR in Southeast Florida rose to 9 ± 4 mm/yr. Our results suggest that engineering solutions to SLR should rely on regional SLR rate projections and not only on the commonly used global SLR projections.
Ezer, Tal. 2016. Can the Gulf Stream induce coherent short-term fluctuations in sea level along the US East Coast? A modeling study. Ocean Dynamics February 2016, Volume 66, Issue 2, pp 207-220 . LINK
Much attention has been given in recent years to observations and models that show that variations in the transport of the Atlantic Meridional Overturning Circulation (AMOC) and in the Gulf Stream (GS) can contribute to interannual, decadal, and multi-decadal variations in coastal sea level (CSL) along the US East Coast. However, less is known about the impact of short-term (time scales of days to weeks) fluctuations in the GS and their impact on CSL anomalies. Some observations suggest that these anomalies can cause unpredictable minor tidal flooding in low-lying areas when the GS suddenly weakens. Can these short-term CSL variations be attributed to changes in the transport of the GS? An idealized numerical model of the GS has been set up to test this proposition. The regional model uses a 1/12° grid with a simplified coastline to eliminate impacts from estuaries and small-scale coastal features and thus isolate the GS impact. The GS in the model is driven by inflows/outflows, representing the Florida Current (FC), the Slope Current (SC), and the Sargasso Sea (SS) flows. Forcing the model with an oscillatory FC transport with a period of 2, 5, and 10 days produced coherent CSL variations from Florida to the Gulf of Maine with similar periods. However, when imposing variations in the transports of the SC or the SS, they induce CSL variations only north of Cape Hatteras. The suggested mechanism is that variations in GS transport produce variations in sea level gradient across the entire GS length and this large-scale signal is then transmitted into the shelf by the generation of coastal-trapped waves (CTW). In this idealized model, the CSL variations induced by variations of ∼10 Sv in the transport of the GS are found to resemble CSL variations induced by ∼5 m s−1 zonal wind fluctuations, though the mechanisms of wind-driven and GS-driven sea level are quite different. Better understanding of the relation between variations in offshore currents and CSL will help to improve the prediction of both short-term water level anomalies that cause flooding, as well as spatial variations in long-term sea level variability and coastal sea level rise.