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Sea level information, and its understanding, are essential for research in oceanography and coastal engineering. This paper describes sea level variability in the Clyde using data from 10 tide gauges. High coherence of sea level variability is found between the Firth of Clyde and estuary of the River Clyde, and between the Firth and estuary and the upstream part of the river. Consequently, if gaps exist in any of the records, missing information can be inferred from others. This applies to timescales of typically hours and longer, appropriate for storm surge or mean sea level change studies. No evidence exists for ‘see-saw’ oscillations of the river on subtidal timescales, as reported for the River Thames, but higher-frequency variability (typical period 45 minutes) is found with equal, or opposite, phase at different river locations. Such a standing wave behaviour would be one of the few reported examples of ‘river seiches’. Data from several agencies are used: two gauges of the UK National Network of the Environment Agency, five from the Scottish Environment Protection Agency, and three from Peel Ports. Only the former tend to be used in academic studies, but the present paper has demonstrated how useful complementary sources can be. [ABSTRACT FROM AUTHOR]

This paper describes a major update to the quasi‐global, higher‐frequency sea‐level dataset known as GESLA (Global Extreme Sea Level Analysis). Versions 1 (released 2009) and 2 (released 2016) of the dataset have been used in many published studies, across a wide range of oceanographic and coastal engineering‐related investigations concerned with evaluating tides, storm surges, extreme sea levels, and other related processes. The third version of the dataset (released 2021), presented here, contains double the number of years of data, and nearly four times the number of records, compared to Version 2. The dataset consists of records obtained from multiple sources around the world. This paper describes the assembly of the dataset, its processing, and its format, and outlines potential future improvements. [ABSTRACT FROM AUTHOR]

A method is described for providing a levelling datum to a sea level record containing hourly heights (or similar) with the use of a second record from a nearby location consisting of high waters only but measured to a known datum. The method is tested using data from a pair of stations in the Thames estuary where there is a predominantly semidiurnal tide. It is then applied to the determination of a datum for an important historical sea level record at Liverpool. The historical background to that important record is explained. The limitations of the method are investigated using data from a pair of stations approximately 50 km apart on the north coast of Wales. This latter case study provides insight into which aspects of the tide contribute to inaccuracies in the method when the stations are some distance apart. [ABSTRACT FROM AUTHOR]

Knowledge of regional changes in mean sea level and local changes in tides are crucial to inform effective climate adaptation. An essential element is the availability of accurate observations of sea level. Sea level data in the Republic of Ireland, prior to the establishment of the National Tide Gauge Network in the mid-2000s, are limited but belie a wealth of historical data available in archival form. In this study, we digitize records located in Cork Harbour, Ireland, from 1842 and show how short-duration (6–8 weeks), high-quality data with a large interval to the present can accurately inform tidal and mean sea level changes. We consider error sources in detail. We estimate for the main M2 tidal constituent that the accuracy of these historical measurements is 1 % and 2 min for amplitude and phase, respectively, once adjustments for seasonal and nodal effects are made. Our mean sea level estimates are accurate to the 2 cm level, once adjustments for atmospheric and seasonal effects are made. Our results show tidal stability with a 2 % change in the amplitude of the M2 component, 4 min change in the phase over a period of 177 years, and mean sea level rise of 40 cm in the Cork Harbour area from 1842 to 2019, approximately in line with global mean sea level trends plus local glacial isostatic adjustment. More broadly, we show that with careful seasonal, nodal, and atmospheric corrections, together with knowledge of benchmark provenance, these historic, survey-oriented data can accurately inform of sea level changes. [ABSTRACT FROM AUTHOR]

We introduce a novel approach to statistically assess the non-linear interaction of tide and non-tidal residual in order to quantify its contribution to extreme sea levels and hence its role in modulating coastal protection levels, globally. We demonstrate that extreme sea levels are up to 30% (or 70 cm) higher if non-linear interactions are not accounted for (e.g., by independently adding astronomical and non-astronomical components, as is often done in impact case studies). These overestimates are similar to recent sea-level rise projections to 2100 at some locations. Furthermore, we further find evidence for changes in this non-linear interaction over time, which has the potential for counteracting the increasing flood risk associated with sea-level rise and tidal and/or meteorological changes alone. Finally, we show how accounting for non-linearity in coastal impact assessment modulates coastal exposure, reducing recent estimates of global coastal flood costs by ~16%, and population affected by ~8%. The non-linear interaction between tide and non-tidal residual impacts current and future extreme water levels. Here, based on 620 gauge records, the authors find a large non-linear interaction in the US East Coast, North Sea and parts of southern Japan, that results in a reduction of extreme sea levels. [ABSTRACT FROM AUTHOR]

We review the characteristics of sea level variability at the coast focussing on how it differs from the variability in the nearby deep ocean. Sea level variability occurs on all timescales, with processes at higher frequencies tending to have a larger magnitude at the coast due to resonance and other dynamics. In the case of some processes, such as the tides, the presence of the coast and the shallow waters of the shelves results in the processes being considerably more complex than offshore. However, 'coastal variability' should not always be considered as 'short spatial scale variability' but can be the result of signals transmitted along the coast from 1000s km away. Fortunately, thanks to tide gauges being necessarily located at the coast, many aspects of coastal sea level variability can be claimed to be better understood than those in the deep ocean. Nevertheless, certain aspects of coastal variability remain under-researched, including how changes in some processes (e.g., wave setup, river runoff) may have contributed to the historical mean sea level records obtained from tide gauges which are now used routinely in large-scale climate research. [ABSTRACT FROM AUTHOR]

Short records of sea level measurements by the Ordnance Survey at 31 locations in 1859-1860, together with recent Mean Sea Level (MSL) information from the UK tide gauge network, have been used to estimate the average rates of sea level change around the coast of Great Britain since the mid-19th century. Rates are found to be approximately 1 mm yr-1 in excess of those expected for the present day based on geological information, providing evidence for a climate-change related component of the increase in UK sea level. In turn, the rates of change of MSL for the past 60 yr are estimated to be ~1 mm yr-1 in excess of the long-term rates since 1859, suggesting an acceleration in the rate of sea level rise between the 19th and 20th/21st centuries. Although the historical records are very short (approximately a fortnight), this exercise in 'data archaeology' shows how valuable to research even the shortest records can be, as long as the measurements were made by competent people and the datums of the measurements were fully documented. [ABSTRACT FROM AUTHOR]

We review the measurement of the mean dynamic topography (MDT) of the Mediterranean using ellipsoidal heights of sea level at discrete tide gauge locations, and across the entire basin using satellite altimetry, subtracting estimates of the geoid obtained from recent models. This 'geodetic approach' to the determination of the MDT can be compared to the independent 'ocean approach' that involves the use of in situ oceanographic measurements and ocean modelling. We demonstrate that with modern geoid and ocean models there is an encouraging level of consistency between the two sets of MDTs. In addition, we show how important geodetic MDT information can be in judging between existing global ocean circulation models, and in providing insight for the development of new ones. The review makes clear the major limitations in Mediterranean data sets that prevent a more complete validation, including the need for improved geoid models of high spatial resolution and accuracy. Suggestions are made on how a greater amount of reliable geo-located tide gauge information can be obtained in the future. [ABSTRACT FROM AUTHOR]

Abstract: Accelerations and inflexions in recent sea-level records are known from instrumental (tide-gauge) datasets, but such records are generally too short to shed light on the question when modern rapid rates of sea-level rise commenced. Proxy sea-level records should therefore also be considered. In this review we compare recent proxy and instrumental sea-level records from the North Atlantic, Australia and New Zealand with the long-term (linear) rate of relative sea-level change that prevailed in the centuries and millennia before the 19th century. We re-evaluate dating models that underpin many of the proxy records and only consider published sea-level index points for which a reliable age can be firmly established. For seven coastal sites we determine the start of recent rapid sea-level rise by identifying the time when sea-level rise first departed from the long-term background rate. We find that within a 40year period, centred around 1925, sea-level rise in all sites started to exceed the late Holocene background rate. This is consistent with local tide-gauge records and also with global and regional tide-gauge compilations. We conclude that proxy and instrumental sea-level datasets record a similar 20th century inflexion. Possible mismatches identified in published literature are therefore reconciled. We suggest that northern hemisphere ice melt, primarily from the Greenland Ice Sheet and small Arctic glaciers, is the main driving mechanism of early 20th century sea-level rise. [Copyright &y& Elsevier]

Two of the most important topics in Sea Level Science are addressed in this paper. One is concerned with the evidence for the apparent acceleration in the rate of global sea level change between the nineteenth and twentieth centuries and, thereby, with the question of whether the twentieth century sea level rise was a consequence of an accelerated climate change of anthropogenic origin. An acceleration is indeed observed in both tide gauge and saltmarsh data at different locations around the world, yielding quadratic coefficients 'c' of order 0.005 mm/year, and with the most rapid changes of rate of sea level rise occurring around the end of the nineteenth century. The second topic refers to whether there is evidence that extreme sea levels have increased in recent decades at rates significantly different from those in mean levels. Recent results, which suggest that at most locations rates of change of extreme and mean sea levels are comparable, are presented. In addition, a short review is given of recent work on extreme sea levels by other authors. This body of work, which is focused primarily on Europe and the Mediterranean, also tends to support mean and extreme sea levels changing at similar rates at most locations. [ABSTRACT FROM AUTHOR]

Relationships were examined between variability in tropical Atlantic sea level and major climate indices with the use of TOPEX/POSEIDON altimeter and island tide gauge data with the aim of learning more about the external influences on the variability of the tropical Atlantic ocean. Possible important connections were found between indices related to the El Niño–Southern Oscillation (ENSO) and the sea levels in all three tropical regions (north, equatorial, and south), although the existence of only one major ENSO event within the decade of available altimetry means that a more complete investigation of the ENSO-dependence of Atlantic sea level changes has to await for the compilation of longer data sets. An additional link was found with the Indian Ocean Dipole (IOD) in the equatorial region, this perhaps surprising observation is probably an artifact of the similarity between IOD and ENSO time series in the 1990s. No evidence was obtained for significant correlations between tropical Atlantic sea level and North Atlantic Oscillation or Antarctic Oscillation Index. The most intriguing relationship observed was between the Quasi-Biennial Oscillation and sea level in a band centered approximately on 10°S. A plausible explanation for the relationship is lacking, but possibilities for further research are suggested. [ABSTRACT FROM AUTHOR]

Tide gauge data and information from tide, surge and ocean models have been used to calculate and validate the Gumbel scale parameters of extreme sea level distributions along the world coastline. The inclusion of ocean model information is found to result in significantly improved correspondence between observed and modelled scale parameters to that obtained using tide and surge model information alone. The scale parameters so obtained are shown to be consistent with findings reported previously, such as in assessments of the Intergovernmental Panel on Climate Change. However, the considerably improved provision of scale parameters along the coast means that coastal planners, and others concerned with impacts of sea level rise, can now undertake more complete investigations of the likely increase in sea level exceedance frequencies. In addition, coastal engineers will have access to more reliable estimates of the 'sea level allowances' needed to design defences for protecting coastal populations. • Extreme sea level Gumbel scale parameters are needed globally for impact studies. • Tide, surge and ocean models are used to calculate them for the world coastline. • The scale parameters are validated using a global collection of tide gauge data. • They will lead to reliable estimates of allowances needed for coastal protection. [ABSTRACT FROM AUTHOR]

A correction to the article "Evidence for Century-Timescale Acceleration in Mean Sea Levels and for Recent Changes in Extreme Sea Levels, published in a previous issue of "Surveys in Geophysics," is presented.

The recent evolution of extreme high waters along the severe cyclone-risk coasts of the Bay of Bengal (the east coast of India and Bangladesh) was assessed using long-term (24–34 years) hourly tide gauge data available from five stations. The highest water levels above mean sea level have the greatest magnitude towards the northern part of the Bay, which decreases towards its south-west. Extreme high waters were observed to result from a combination of moderate, or even small, surges with large tides at these stations in most of the cases. Increasing trends, which are significant, were observed in the extreme high waters at Hiron Point, at the head of the Bay. However, the trends in extremes are slightly lower than its mean sea level trend. For the other stations, Cox's Bazaar, Paradip Visakhapatnam and Chennai, no significant trends were observed. At inter-annual time scales, changes in extreme high waters in the Bay of Bengal were found to be influenced by the El Niño Southern Oscillation and the Indian Ocean Dipole. [ABSTRACT FROM AUTHOR]

Abstract: Long term mean sea level in the Chagos Archipelago has been relatively stable over the ~20year length of the available instrumental records. Tide-gauge data from Diego Garcia (1988–2000, and 2003–2011) show no statistically significant long-term rise, whilst the rates of rise obtained from the satellite altimeter record for 1993–2011 span the range of 0.16–4.56mmyr−1 in the surrounding sea areas (70–74°E and 4–9°S) and are also consistent with a zero rate except in the far south of the region. The dominant feature is one of considerable inter-annual variability in mean sea level of up to ~10cm, such that the very weak seasonal pattern of highest and lowest sea level in February and May respectively, is absent or reversed in some years. The Indian Ocean Dipole appears to exert an important influence on mean sea level in the area, with positive and negative dipole mode indices preceding periods of elevated or lowered sea levels respectively. The Chagos also lie outside the Indian Ocean cyclone belt and experience relatively low wind speeds, and there is no evidence of changes in the wind or wave environment in the past 20years. Although in an area of seismic activity, there is no record of island subsidence, indeed on Diego Garcia minor crustal uplift of 0.63±0.28SEmmyr−1 has occurred between 1996 and 2009. Collectively, these results suggest that this has been a relatively stable physical environment, and that these low-lying coral islands should continue to be able to support human habitation, as they have done for much of the last 200years. Nonetheless, future sea-level rise and its effect on the Chagos remains an important issue for further studies such as those of the Intergovernmental Panel on Climate Change. [Copyright &y& Elsevier]

Changing sea levels will have a major impact on human life over the next 100 years. We need mean sea level data to study climate change, the impact of human activities on densely populated areas and the economic impacts of sea level rise, and to plan coastal engineering. The Permanent Service for Mean Sea Level (PSMSL) is the global databank for long-term mean sea level data.The PSMSL operates under the auspices of the International Council for Science (ICSU), is a regular member of the ICSU World Data System and is associated with the International Association for the Physical Sciences of the Oceans (IAPSO) and the International Association of Geodesy (IAG). The PSMSL continues to work closely with other members of the sea level community through the Intergovernmental Oceanographic Commission's Global Sea Level Observing System (GLOSS).Following an analysis of the international community and our users, we propose growth areas to focus on, including new products and services. The primary goal of the PSMSL is to expand the database and fill gaps in the observational network by the use of novel techniques (e.g. automatic quality control of tide gauge data) and technologies (e.g. GNSS reflectometry). We will continue our core mission of processing global mean sea level data and plan to create an archive for and deliver GNSS reflectometry data. We will provide training and automatic processing software to tide gauge operators and scientists.In a world of big data, we can no longer control what happens to our distributed product. We must make sure what we provide is properly and fully described. We need to be able to produce a full audit trail showing where data (and metadata) came from and, if we have updated records, why. This will in part be achieved by producing an annual digital object identifier (DOI) for the PSMSL dataset and beginning to digitise the paper records containing site metadata, correspondence, adjustments etc. We will lead the development of standards for sea level data and metadata and work towards making our data findable, accessible, interoperable and reusable (FAIR). [ABSTRACT FROM AUTHOR]

The article offers information on the challenge in the collection of Permanent Service for Mean Sea Level (PSMSL) dataset of long term sea level change from tide gauges. It discusses the changes of observation methods including the sensors used, the locations, and organisation responsible to measure the changes in sea level. It adds that inclusion of metadata in PSMSL dataset will require sorting of high frequency data to monthly mean data that removes tidal cycle.