Sea Level Rise and Future Projections in the Baltic Sea

Based on the updated relative sea level rise rates, 21st-century projections are made for the west coast of Portugal Mainland. The mean sea level from Cascais tide gauge and North Atlantic satellite altimetry data have been analyzed. Through bootstrapping linear regression and polynomial adjustments, mean sea level time series were used to calculate different empirical projections for sea level rise, by estimating the initial velocity and its corresponding acceleration. The results are consistent with an accelerated sea level rise, showing evidence of a faster rise than previous century estimates. Based on different numerical methods of second order polynomial fitting, it is possible to build a set of projection models of relative sea level rise. Applying the same methods to regional sea level anomaly from satellite altimetry, additional projections are also built with good consistency. Both data sets, tide gauge and satellite altimetry data, enabled the development of an ensemble of projection models. The relative sea level rise projections are crucial for national coastal planning and management since extreme sea level scenarios can potentially cause erosion and flooding. Based on absolute vertical velocities obtained by integrating global sea level models, neo-tectonic studies, and permanent Global Positioning System (GPS) station time series, it is possible to transform relative into absolute sea level rise scenarios, and vice-versa, allowing the generation of absolute sea level rise projection curves and its comparison with already established global projections. The sea level rise observed at the Cascais tide gauge has always shown a significant correlation with global sea level rise observations, evidencing relatively low rates of vertical land velocity and residual synoptic regional dynamic effects. An ensemble of sea level projection models for the 21st century is proposed with its corresponding probability density function, both for relative and absolute sea level rise for the west coast of Portugal Mainland. A mean sea level rise of 1.14 m was obtained for the epoch of 2100, with a likely range of 95% of probability between 0.39 m and 1.89 m.

Researchers agree that there are two main causes to sea-level rise: melting of land-ice and thermal expansion of ocean water due to global climate warming. However there exist several secondary causes that can result in sea level rise, which used to be ignored. In this study we firstly qualitatively analyzed several secondary reasons that can also cause sea level rise such as land reclamation projects, coastal erosion, river sediment, and so on. Then a mathematical model was built, by the model we quantitatively estimated the sea level rise rates that caused by river sediment and all terrestrial materials discharged into the sea. The concept of “absolute sea level rise” and “relative sea level rise” were put forward in this process, “absolute sea level rise” means the sea level rise compared with level surface, “relative sea level rise” means the sea level rise compared with the land surface. The “relative sea level rise” rate usually greater than “absolute sea level rise” rate because of the terrestrials discharged into the sea not only result in sea level rise but also cause land surface decrease. Our calculation result shows that terrestrial material input could cause an absolute sea level rise by about 0.03484mm per year, and a relative sea level rise by 0.1327 mm per year. All the terrestrial materials into the sea could cause absolute sea-level rise by 0.04099mm per year, and relative rise by about 0.1561mm. Although the relative sea-level rise rate of terrestrial material input is about only one-tenth of the current sea-level rise rate, this is a one-way and persistent process. From a long-term point of view, we also should pay attentions to this process.

Transgressive wave- and tide-dominated barrier-lagoon system and sea-level rise since 8.2 ka recorded in sediments in northern Bohai Bay, China

Empirical studies and climate models suggest large variations of absolute sea level (ASL) changes between oceanic basins. Such potential variations raise concern on the applicability of global mean ASL predictions to specific regions and on estimates of relative sea level (RSL) hazards. We address this issue for the western Canada and northwestern United States coastline by estimating the 20th century ASL rate using a combination of 34 colocated tide gauge and Global Positioning System (GPS) stations. The tide gauge data are quality controlled and corrected for spatially and temporally correlated sea level transients in order to derive robust RSL trends and standard errors. Reference frame and other GPS‐specific issues are considered as part of the error budget in absolute GPS vertical velocities. Our combined tide gauge‐GPS analysis, aligned to the International Terrestrial Reference Frame 2000, indicates a northeast Pacific ASL rise of 1.8 ± 0.2 mm/a through the 20th century, which is similar to accepted rates for the global eustatic mean. For the period 1993–2003, we find a regional ASL rate of −4.4 ± 0.5 mm/a consistent with satellite altimetry. On the basis of the Intergovernment Panel on Climate Change Assessment Report 4 mean scenario and our assessment of coastal motions from GPS and tide gauge data, we derive a map of predicted 21st century RSL rise in western Canada and the northwestern United States. Variations in coastal uplift strongly affect spatial RSL patterns. Subsidence of southern Puget Sound may significantly increase RSL rise in the Seattle‐Tacoma metropolitan area. Conversely, tectonic uplift along parts of the outer west coast may reduce future RSL rise by up to 50–100%.

The nature and impact of relative sea level rise on the coastal areas of Bangladesh: trend analysis and vulnerability assessment

The Chesapeake Bay (CB) is the largest estuary in the United States, and a large bolide crashed into it 35 million years ago. This study analyzed observations from seven pairs of closely spaced tide gauges (TG) and GPS stations around the CB to simulate relative sea level rise (RSLR) since the 20th century. Outcrops or subcrops are pre-Cretaceous (pre-C), Cretaceous (C), Tertiary (T), and Quaternary (Q) from the Northwest to the Southeast in the CB coastal plain. RSLR at TG is assumed to be the sum of paired GPS-detected land subsidence (LS) and absolute sea level rise (ASLR) in this paper. Before 1992 in the 20th century, TG Washington, DC, located in the pre-C outcrop/subcrop zone appears to have RSLR and LS rates of (2.68, 1.58) mm/year; TG Baltimore in the C zone (3.0, 1.9) mm/year; TGs Annapolis, Cambridge, and Solomon Island in the T zone (3.39, 2.24) mm/year, (3.45, 2.34) mm/year, and (3.75, 2.66) mm/year, respectively; and TGs Kiptopeke and Yorktown in the Q zone (4.05, 2.95) mm/year and (3.06, 1.96) mm/year, respectively. The LS rate increases from the pre-C through Q zones except the Yorktown station impacted by the crater; the ASLR before 1992 in the 20th century in the CB area is in the range of 1.10 mm/year–1.15 mm/year by removing LS from RSLR at above seven TG locations.

Sea-level rise enhances carbon accumulation in United States tidal wetlands

Global mean sea level (GMSL) has risen by about 7-8 inches (about 16-21 cm) since 1900, with about 3 of those inches (about 7 cm) occurring since 1993. Human-caused climate change has made a substantial contribution to GMSL rise since 1900, contributing to a rate of rise that is greater than during any preceding century in at least 2,800 years. Relative to the year 2000, GMSL is very likely to rise by 0.3-0.6 feet (9-18 cm) by 2030, 0.5-1.2 feet (15-38 cm) by 2050, and 1.0-4.3 feet (30-130 cm) by 2100. Future pathways have little effect on projected GMSL rise in the first half of the century, but significantly affect projections for the second half of the century. Emerging science regarding Antarctic ice sheet stability suggests that, for high emission scenarios, a GMSL rise exceeding 8 feet (2.4 m) by 2100 is physically possible, although the probability of such an extreme outcome cannot currently be assessed. Regardless of pathway, it is extremely likely that GMSL rise will continue beyond 2100. Relative sea level (RSL) rise in this century will vary along U.S. coastlines due, in part, to changes in Earth's gravitational field and rotation from melting of land ice, changes in ocean circulation, and vertical land motion (very high confidence). For almost all future GMSL rise scenarios, RSL rise is likely to be greater than the global average in the U.S. Northeast and the western Gulf of Mexico. In intermediate and low GMSL rise scenarios, RSL rise is likely to be less than the global average in much of the Pacific Northwest and Alaska. For high GMSL rise scenarios, RSL rise is likely to be higher than the global average along all U.S. coastlines outside Alaska. Almost all U.S. coastlines experience more than global mean sea level rise in response to Antarctic ice loss, and thus would be particularly affected under extreme GMSL rise scenarios involving substantial Antarctic mass loss. As sea levels have risen, the number of tidal floods each year that cause minor impacts (also called nuisance floods) have increased 5- to 10-fold since the 1960s in several U.S. coastal cities. Rates of increase are accelerating in over 25 Atlantic and Gulf Coast cities. Tidal flooding will continue increasing in depth, frequency, and extent this century. Assuming storm characteristics do not change, sea level rise will increase the frequency and extent of extreme flooding associated with coastal storms, such as hurricanes and nor'easters. A projected increase in the intensity of hurricanes in the North Atlantic could increase the probability of extreme flooding along most of the U.S. Atlantic and Gulf Coast states beyond what would be projected based solely on RSL rise. However, there is low confidence in the projected increase in frequency of intense Atlantic hurricanes, and the associated flood risk amplification and flood effects could be offset or amplified by such factors as changes in overall storm frequency or tracks.

Relative sea level rise at tide gauge Galveston Pier 21, Texas, is the combination of absolute sea level rise and land subsidence. We estimate subsidence rates of 3.53 mm/a during 1909–1937, 6.08 mm/a during 1937–1983, and 3.51 mm/a since 1983. Subsidence attributed to aquifer-system compaction accompanying groundwater extraction contributed as much as 85% of the 0.7 m relative sea level rise since 1909, and an additional 1.9 m is projected by 2100, with contributions from land subsidence declining from 30 to 10% over the projection interval. We estimate a uniform absolute sea level rise rate of 1.10 mm ± 0.19/a in the Gulf of Mexico during 1909–1992 and its acceleration of 0.270 mm/a2 at Galveston Pier 21 since 1992. This acceleration is 87% of the value for the highest scenario of global mean sea level rise. Results indicate that evaluating this extreme scenario would be valid for resource-management and flood-hazard-mitigation strategies for coastal communities in the Gulf of Mexico, especially those affected by subsidence.

Abstract. Sea level rise (SLR) is a major concern for Europe, where 30 million people live in the historical 1-in-100-year event flood coastal plains. The latest IPCC assessment reports provide a literature review on past and projected SLR, and their key findings are synthesized here with a focus on Europe. The present paper complements IPCC reports and contributes to the Knowledge Hub on SLR European Assessment Report. Here, the state of knowledge of observed and 21st century projected SLR and changes in extreme sea levels (ESLs) are documented with more regional information for European basins as scoped with stakeholders. In Europe, satellite altimetry shows that geocentric sea level trends are on average slightly above the global mean rate, with only a few areas showing no change or a slight decrease such as central parts of the Mediterranean Sea. The spatial pattern of geocentric SLR in European Seas is largely influenced by internal climate modes, especially the North Atlantic Oscillation, which varies on year-to-year to decadal timescales. In terms of relative sea level rise (RSLR), vertical land motions due to human-induced subsidence and glacial isostatic adjustment (GIA) are important for many coastal European regions, leading to lower or even negative RSLR in the Baltic Sea and to large rates of RSLR for subsiding coastlines. Projected 21st century local SLR for Europe is broadly in line with projections of global mean sea level rise (GMSLR) in most places. Some European coasts are projected to experience a RSLR by 2100 below the projected GMSLR, such as the Norwegian coast, the southern Baltic Sea, the northern part of the UK, and Ireland. A relative sea level fall is projected for the northern Baltic Sea. RSLR along other European coasts is projected to be slightly above the GMSLR, for instance the Atlantic coasts of Portugal, Spain, France, Belgium, and the Netherlands. Higher-resolution regionalized projections are needed to better resolve dynamic sea level changes especially in semi-enclosed basins, such as the Mediterranean Sea, North Sea, Baltic Sea, and Black Sea. In addition to ocean dynamics, GIA and Greenland ice mass loss and associated Earth gravity, rotation, and deformation effects are important drivers of spatial variations of projected European RSLR. High-end estimates of SLR in Europe are particularly sensitive to uncertainties arising from the estimates of the Antarctic ice mass loss. Regarding ESLs, the frequency of occurrence of the historical centennial-event level is projected to be amplified for most European coasts, except along the northern Baltic Sea coasts where a decreasing probability is projected because of relative sea level fall induced by GIA. The largest historical centennial-event amplification factors are projected for the southern European seas (Mediterranean and Iberian Peninsula coasts), while the smallest amplification factors are projected in macro-tidal regions exposed to storms and induced large surges such as the southeastern North Sea. Finally, emphasis is given to processes that are especially important for specific regions, such as waves and tides in the northeastern Atlantic; vertical land motion for the European Arctic and Baltic Sea; seiches, meteotsunamis, and medicanes in the Mediterranean Sea; and non-linear interactions between drivers of coastal sea level extremes in the shallow North Sea.

Onset of runaway fragmentation of salt marshes

Absolute sea-level rise has become an important topic globally due to climate change. In addition, relative sea-level rise due to the vertical land motion in coastal areas can have a big societal impact. Vertical land motion (VLM) in Southeast Asia includes a tectonically induced component: uplift and subsidence in plate boundary zones where both Peninsular and East Malaysia are located. In this paper, the relative sea-level trends and (seismic cycle-induced) temporal changes across Malaysia were investigated. To do so, the data (1984–2019) from 21 tide gauges were analyzed, along with a subset (1994–2021) of nearby Malaysian GNSS stations. Changes in absolute sea level (ASL) at these locations (1992–2021) were also estimated from satellite altimetry data. As a first for Peninsular and East Malaysia, the combination ASL minus VLM was robustly used to validate relative sea-level rise from tide-gauge data and provide relative sea-level trend estimates based on a common data period of 25+ years. A good match between both the remote and in situ sea-level rise estimations was observed, especially for Peninsular Malaysia (differences < 1 mm/year), when split trends were estimated from the tide gauges and GNSS time series to distinguish between the different VLM regimes that exist due to the 2004 Sumatra–Andaman megathrust earthquake. As in the south of Thailand, post-seismic-induced negative VLM has increased relative sea-level rise by 2–3 mm/year along the Andaman Sea and Malacca Strait coastlines since 2005. For East Malaysia, the validation shows higher differences (bias of 2–3 mm/year), but this poorer match is significantly improved by either not including data after 1 January 2014 or applying a generic jump to all East Malay tide gauges from that date onwards. Overall, the present relative sea-level trends range from 4 to 6 mm/year for Malaysia with a few regions showing up to 9 mm/year due to human-induced land subsidence.

Changes to mean sea level and/or sea level extremes (e.g., storm surges) will lead to changes in coastal impacts. These changes represent a changing exposure or risk to our society. Here, we present 21st century sea-level projections for Norway largely based on the Fifth Assessment Report from the Intergovernmental Panel for Climate Change (IPCC AR5). An important component of past and present sea-level change in Norway is glacial isostatic adjustment. We therefore pay special attention to vertical land motion, which is constrained using new geodetic observations with improved spatial coverage and accuracies, and modelling work. Projected ensemble mean 21st century relative sea-level changes for Norway are, depending on location, from −0.10 to 0.30 m for emission scenario RCP2.6; 0.00 to 0.35 m for RCP 4.5; and 0.15 to 0.55 m for RCP8.5. For all RCPs, the projected ensemble mean indicates that the vast majority of the Norwegian coast will experience a rise in sea level. Norway’s official return heights for extreme sea levels are estimated using the average conditional exceedance rate (ACER) method. We adapt an approach for calculating sea level allowances for use with the ACER method. All the allowances calculated give values above the projected ensemble mean Relative Sea Level (RSL) rise, i.e., to preserve the likelihood of flooding from extreme sea levels, a height increase above the most likely RSL rise should be used in planning. We also show that the likelihood of exceeding present-day return heights will dramatically increase with sea-level rise.

Depositional environments and sequence stratigraphy of paralic glacial, paraglacial and postglacial Upper Ordovician siliciclastic deposits in the Murzuq Basin, SW Libya

Relative sea level rise increases the vulnerability of coastal infrastructure to storm surge flooding. In this study, we develop, validate, and apply a coupled hydrodynamic and wave model to simulate storm surge inundation under different local sea level projections to quantitatively assess some of these vulnerabilities. Our study area is located in southeast Virginia, where the rate of relative sea level rise is the highest in the US East Coast. The model is developed in two levels of nesting in which a region-scale model with relatively low resolution provides boundary conditions for a high-resolution city-scale model. The model is first validated with documented water levels in water and over land during Hurricane Irene (2011). It is then applied to investigate changes in vulnerability of transportation infrastructure to relative sea level rise by quantifying changes in flood intensity and duration over access roads to critical bridges that are identified based on elevation and traffic volume. Furthermore, the length of flooded roadways as well as the extent and volume of inundation is quantified under different combinations of relative sea level rise and storm return periods. With a 1.8-m sea level rise, an upper bound of sea level projections in the study area in 2070, and under 10- and 50-year storms, collective flood intensity and duration increase by factors of 23 and 51, respectively, and the length of flooded roadways increase by factors of 9 and 7 from their present values, respectively. Variations in flood intensity, duration, area, and volume under storm and sea level rise combinations indicate that storm surge response to relative sea level rise is generally nonlinear, and linear superposition of these factors mostly overestimates inundation intensity while consistently overestimating inundation volume. Variation of rate of change in total inundation volume is more complex and suggests that the linear summation overestimates flood volume for small to moderate rates of sea level rise while it underpredicts flood volume for high sea level projections. This suggests that nonlinear effects act to intensify flood vulnerability at an accelerated rate as sea level rises.