CL4.9 | Understanding sea level changes: global to local, from past to future
EDI
Understanding sea level changes: global to local, from past to future
Co-organized by OS1
Convener: Aimée Slangen | Co-conveners: Carolina M.L. CamargoECSECS, Svetlana Jevrejeva, Julius OelsmannECSECS, M. D. Palmer
Orals
| Fri, 19 Apr, 08:30–12:25 (CEST)
 
Room F1
Posters on site
| Attendance Thu, 18 Apr, 16:15–18:00 (CEST) | Display Thu, 18 Apr, 14:00–18:00
 
Hall X5
Posters virtual
| Attendance Thu, 18 Apr, 14:00–15:45 (CEST) | Display Thu, 18 Apr, 08:30–18:00
 
vHall X5
Orals |
Fri, 08:30
Posters on site |
Thu, 16:15
Posters virtual
Thu, 14:00
To address societal concerns over rising sea level and extreme events, understanding and quantifying the contributions behind these changes is key to anticipate potential impacts of sea level change on coastal communities and the global economy. In this session, we address these challenges and we welcome contributions from the international sea level community that improve our knowledge of the past, present and future changes in global and regional sea level, extreme events and coastal impacts.
We focus on studies exploring the physical mechanisms for sea level rise and variability and the drivers of these changes, at any time scale (from high-frequency phenomena to paleo sea level). Investigations on linkages between variability in sea level, heat and freshwater content, ocean dynamics, land subsidence and mass exchanges between the land and the ocean associated with ice sheet and glacier mass loss and changes in the terrestrial water storage are welcome. Studies focusing on future sea level changes are also encouraged, as well as those discussing potential short-, medium-, and long-term impacts on coastal environments, as well as the global oceans.

Please note that for this session the posters are on Thursday afternoon, and the talks are on Friday morning.

Orals: Fri, 19 Apr | Room F1

Chairpersons: Aimée Slangen, Carolina M.L. Camargo
Past sea-level changes
08:30–08:40
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EGU24-5010
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ECS
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On-site presentation
Mid Holocene relative sea-level changes from coral microatolls of Pulau Biola, Singapore  
Jennifer Quye-Sawyer, Jing Ying Yeo, Wan Lin Neo, Zihan Aw, Lin Thu Aung, Nurul Syafiqah Tan, Junki Komori, Ke Lin, Xianfeng Wang, and Aron J. Meltzner

Coral microatolls are precise proxies of relative sea-level (RSL) change in low-latitude coastal regions. These coral colonies live in the intertidal zone where partial mortality due to low-water events produces a characteristic planform ring structure. Since ring elevations reflect changes in local RSL during a coral’s lifetime, we can use the surface profiles of microatolls to quantify short-term (decadal) rates of RSL change. Therefore, Holocene fossil microatolls can produce sea-level index points (SLIPs) with relatively high spatial and temporal resolution. In this study, we present preliminary sea-level reconstructions from Pulau Biola (Violin Island), Singapore, based upon several Porites sp. and Diploastrea heliopora fossil microatolls. We calculated the difference in elevation between the fossils and local living microatolls of the same genus to quantify the magnitude of past water level. We also combined U-Th ages, structure-from-motion photogrammetry and LiDAR 3D models, and survey data to generate a RSL history spanning more than two centuries in the mid Holocene. The highest-elevation fossil microatolls at Pulau Biola are consistent with an overall rise in sea level, from 0.2 to 0.7 m above present, between 7.7 and 7.4 kyr BP. In addition, decimetre-scale sea-level fluctuations during this period are inferred from decreasing and increasing ring elevations within corals. These fluctuations indicate a more complex sea-level history than resolved by other proxies or glacial isostatic adjustment models, and ongoing work aims to reconcile conflicting Holocene sea-level models and datasets in the Singapore region.

How to cite: Quye-Sawyer, J., Yeo, J. Y., Neo, W. L., Aw, Z., Aung, L. T., Tan, N. S., Komori, J., Lin, K., Wang, X., and Meltzner, A. J.: Mid Holocene relative sea-level changes from coral microatolls of Pulau Biola, Singapore , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5010, https://doi.org/10.5194/egusphere-egu24-5010, 2024.

08:40–08:50
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EGU24-1007
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ECS
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On-site presentation
Comparing altimetry-derived coastal sea level anomaly with tide gauge observations along the global coastline by accounting for shelf-width  
Vandana Sukumaran and Bramha Dutt Vishwakarma

It is expected that sea level rise and resulting coastal flooding will cost us over 1 trillion dollars annually by 2050. Therefore, understanding and monitoring coastal sea level rise is vital. Tide Gauges are in-situ instruments that have been providing sea level measurements since the 1800s, but they are sparse, and data availability is limited. Therefore, ocean altimetry has been the preferred observational tool for monitoring global sea levels.  

Satellite altimetry has been providing extensive and continuous global sea level data for more than three decades now. However, extracting reliable data close to the coast has been problematic due to signal contamination from land or calm water and lack of accurate geophysical corrections. Recently dedicated coastal altimetry products were proposed to provide better coastal sea level change product.   

In this study, we compare coastal altimetry products XTRACK-1Hz, XTRACK/ALES-20Hz in observing Sea Level Anomalies (SLA) with Tide Gauges (TG) along the global coastline from 2002-2019. 458 stations were selected for the study after applying several selection criteria that address data gaps, data availability from TG, altimetry, and correction products. The SLA signals from TG were decomposed into non-linear trend, seasonal, and residual components using Seasonal-Trend Decomposition using Loess (STL) method. The correlation coefficient, Root Mean Square Error (RMSE), and Index of Agreement (IOA) were computed for interannual and residual signals from TG and coastal altimetry products. Linear sea level trends at each station were also estimated from altimetry and TG observations after correcting for GPS-derived vertical land motion (VLM). 

When using altimetry for sea level signals near the coast, it is important to select point observations carefully instead of using a search radius that may take points from adjacent regions that could behave differently due to different coastal ocean processes. We developed a dynamically varying search radius for each TG, a function of the coastal shelf width near that station, to collate satellite observations as a representative of coastal sea level change. All the altimetry observations that fall within the search radius and are less than 25 km along the coast are used for comparison. In several cases, due to the sharp changes in the coastal morphology, the sea level signals seen by the adjacent TG stations are quite different, and thus, the reliability of altimetry suffered. 

With our analysis approach, we found good agreement between all altimetry products (XTRACK, XTRACK/ALES), and TG at residual and non-linear trend scales. A few stations near the fault lines and other tectonic regions disagree with altimetry trend estimates due to strong VLM signals that are not completely resolved by the VLM product used for correction. Around 70% of stations had a good agreement (r > 0.7) with trend and 55% with residual components. High-resolution (20Hz) XTRACK/ALES provided more observations near the coast. Nevertheless, both XTRACK/ALES-20Hz and XTRACK-1Hz performed well. This novel approach to select representative observation points from altimetry for a coastal zone will provide improved coastal sea level products from satellites, which can be considered at par with TG observations. 

How to cite: Sukumaran, V. and Vishwakarma, B. D.: Comparing altimetry-derived coastal sea level anomaly with tide gauge observations along the global coastline by accounting for shelf-width , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1007, https://doi.org/10.5194/egusphere-egu24-1007, 2024.

08:50–09:00
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EGU24-20096
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ECS
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Virtual presentation
Attributing low-frequency variations in ocean water mass redistribution during 2002-2020 
Shanshan Deng, Yuxin Liu, Wenxi Zhang, and Ange Hu

Studying how ocean water mass is redistributed can help with a better understanding of the regional sea level change. This study investigates the roles of the different physical processes involved in low-frequency ocean water mass, including the sea level fingerprint and the dynamic ocean mass change, from regional to global scales over the period 2004-2021. Global water mass redistribution data from the GRACE and GRACE-FO satellites were used, as well as surface wind and sea surface temperature data from the ERA5 reanalysis. The sea-level equation is used to simulate the sea level fingerprint, and the maximum covariance analysis is used to extract possible signals of the wind-forcing and temperature-gradient-forcing ocean mass redistribution. The results show that the low-frequency ocean water mass is dominated by the long-term trend and the decadal-like fluctuation. Sea level fingerprint significantly contributes to the open ocean. Compared with temperature gradients, wind forcing plays a more important role in dynamic ocean mass redistribution. The wind-forcing dynamic processes significantly drive the anomalies near the North Indian Ocean, North Atlantic Ocean, South Pacific Ocean, and some marginal seas. After removing the sea level fingerprint and ocean dynamics, some non-negligible noise, located in seismic zones, was also found, suggesting the misestimation of seafloor deformation resulting from earthquakes in the GRACE/GRACE-FO data processing. These findings may improve our understanding of the long-term anomalies in regional and global sea levels.

How to cite: Deng, S., Liu, Y., Zhang, W., and Hu, A.: Attributing low-frequency variations in ocean water mass redistribution during 2002-2020, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20096, https://doi.org/10.5194/egusphere-egu24-20096, 2024.

09:00–09:10
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EGU24-19016
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On-site presentation
Estimating the long-term sea-level contribution from shelf mass loading on the Norwegian shelf using hydrographic in-situ data, satellite altimetry and GRACE 
Kristin Richter, Fabio Mangini, Antonio Bonaduce, and Roshin Raj

Future sea-level rise on shallow continental shelves differs in one important aspect from open ocean sea-level rise: the local steric effect, that is the change in the water column height due to changes in sea water density, plays a minor role compared to the much deeper open ocean. Instead, the bulk of oceanic sea-level rise on continental shelves arises from an increase in ocean water mass that is being imported from the open ocean – the so-called shelf mass loading (SML). This redistribution is mainly driven by thermal expansion of water masses below shelf depth and magnifies as the subsurface ocean layers continue to warm.

 

Few studies have tried to detect SML as the signal is only expected to become dominant over decadal to multidecadal periods given the large natural variability in shallow regions.

Here, we combine hydrographic data from a section crossing the Norwegian shelf, with observations of total sea-level change from altimetry and estimates of mass changes from GRACE gravity missions to estimate the strength of SML over the past decades. We compare the residual of total sea level (from altimetry) and steric height (from hydrography) with GRACE estimates from three different solutions. Over the common period (2002 -2020), both estimates show a consistently higher trend over the shallow shelf area compared to the deep ocean. We estimate the shelf mass contribution in the order of 0.5 – 1.0 mm/yr, depending on the GRACE solution selected.

How to cite: Richter, K., Mangini, F., Bonaduce, A., and Raj, R.: Estimating the long-term sea-level contribution from shelf mass loading on the Norwegian shelf using hydrographic in-situ data, satellite altimetry and GRACE, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19016, https://doi.org/10.5194/egusphere-egu24-19016, 2024.

09:10–09:20
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EGU24-14809
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On-site presentation
Sea Level Change in the East China Sea Inferred from Satellite Gravimetry, Altimetry and Steric Datasets
(withdrawn)
Fengwei Wang, Jianhua Geng, Yunzhong Shen, Jianli Chen, Anny Cazenave, and Qiujie Chen
09:20–09:30
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EGU24-2405
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On-site presentation
Modelling of Low Frequency Sea Level Variability Over the Maritime Continent: Historical Dynamic Variability and Changes 
Peifeng Ma, Nidheesh Gangadharan, and Pavel Tkalich

Dynamical downscaling employing high-resolution ocean models is widely considered as an efficient approach for modelling of regional ocean dynamics and sea-level changes using output of original coarse-resolution global general circulation models (GCMs). In this study, the historical dynamic variability and trends of sea level in the South China Sea (SCS) and the Southeast Asia Seas (SEAS) are investigated using the high-resolution regional ocean model (NEMO). Two hindcast ocean modelling experiments are conducted for the period 1960-2014. One is driven by global reanalysis data (ERA5 and ORAS5) forcings at the lateral and surface boundaries. The other is driven by global modelling oceanic data (EC-EARTH3) at the lateral boundary and by WRF-based downscaled atmospheric fields from the same parent model (EC-Earth3) at the surface boundary. Using the hindcast model runs, variability and trends of low-frequency sea-levels, as well as the driving mechanisms and the related processes are discussed, and the model performance and biases are analysed.

This Research is supported by Singapore’s National Research Foundation and National Environment Agency under the National Sea Level Programme Funding Initiative (Award No. USS-IF-2020-4).

How to cite: Ma, P., Gangadharan, N., and Tkalich, P.: Modelling of Low Frequency Sea Level Variability Over the Maritime Continent: Historical Dynamic Variability and Changes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2405, https://doi.org/10.5194/egusphere-egu24-2405, 2024.

09:30–09:40
Discussion
09:40–09:50
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EGU24-18660
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ECS
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On-site presentation
Understanding the Regional Disparity of the Sea Level Rise during Altimetry Era 
Rong Deng and Wenjie Dong

The application of satellite altimetry allows us to acquire global sea level height data with higher spatial and temporal resolution, enabling a systematic understanding of spatial differences in sea level rise. In our study, we reconstructed the barystatic sea level and steric sea level change during the altimetry era (1993-2022). This involved utilizing mass change data and ocean heat content data from various sources. Notably, we incorporated the latest observation and model-simulation data, ensuring coverage of the entire altimetry era compared with previous reconstructions. Based on altimetry-observed relative sea level change, the global sea level rise rate is 3.38 [3.09 3.68] mm/yr, the global barystatic and steric sea level change is 1.80 [1.45 2.15] mm/my, and 1.02 [0.67 1.37] mm/yr, respectively. Subsequently, we further analyzed the regional characteristics of these sea level rises.

Over the past three decades, sea levels have exhibited a faster rate of increase in the western basins, as well as in the equatorial and mid-latitude region, surpassing the global average. Conversely, sea level rise at higher latitudes has been relatively slower than the global average. In the mid-low latitude regions, the higher rate of sea level rise is primarily dominated by the expansion of ocean water due to its heating. In high-latitude regions, the lower sea level rise rate is primarily attributed to the far-field effects of the melting of land ice. The distribution of halosteric sea level changes is nearly uniform across latitudes. However, in the western Atlantic, a significant counteracting effect against the rise in thermosteric sea level is observed. This is linked to the weakening Atlantic Meridional Overturning Circulation (AMOC).

Furthermore, we selected 8 regions, North Pacific (NP), South China Sea (SCS), Western Tropical Pacific (WTP), Bay of Bengal (BOB), Tropical Indian Ocean (TIO), Southwest Pacific (SWP), Gulf of Mexico (GOM), and North Atlantic (NA), with sea level rise rates faster than the global average. We analyzed the contributions of different components to the sea level rise in these areas. These regions are all adjacent to land or have a significant number of islands, the faster sea level rise poses a greater threat to the corresponding coastal areas. The contributions of barystatic and steric sea level components are approximately equal in most of these regions. However, in SCS and GOM, the contributions of the barystatic component exceed 60%. The halosteric sea level has a significant negative contribution to the sea level rise in the GOM and NA. The Antarctic Ice Sheet and Greenland Ice Sheet melting contribute to sea level rise in these regions by less than 15%, and more than 15%, respectively. The highest contribution of glacier melting is in the SCS, approximately 23%. Compared to the melting of land ice, changes in land water contribute limitedly to sea level rise in these regions. The contribution is less than 10%, except for in NA.

How to cite: Deng, R. and Dong, W.: Understanding the Regional Disparity of the Sea Level Rise during Altimetry Era, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18660, https://doi.org/10.5194/egusphere-egu24-18660, 2024.

09:50–10:00
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EGU24-3440
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ECS
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On-site presentation
Quantifying the impact of near-surface winds on the occurrence of extreme sea level rises along the Swedish Baltic coastline: A statistical analysis 
Lorenzo Minola, Alice Re, Shalenys Bedoya-Valestt, Corrado Motta, Cesar Azorin-Molina, Alessandro Pezzoli, and Deliang Chen

Sea level rises pose significant risks to densely populated coastal regions, threatening human lives and vital infrastructures. Coastal societies, economies, and properties face acute vulnerability from saltwater intrusion, coastal erosion, and flooding resulting from extreme sea level variations. These occurrences are a confluence of factors, including local sea level rises, tidal changes, storm surges, waves, and shifts in coastal morphology.

In the Baltic Sea basin, where tides and North Atlantic storm surges are mitigated by the Danish Straits due to its semi-enclosed nature, coastal extreme sea levels are primarily driven by storm surges propelled by atmospheric pressure and surface winds from extratropical cyclones. Consequently, the surge in extreme sea levels here is predominantly wind-induced, regulated by meteorological processes.

This research focuses on the meteorological conditions, specifically wind patterns, that contribute to sudden sea level rises along the Swedish Baltic coastline. By integrating observations and model data like the ERA5 reanalysis, the study correlates the rapid increase in relative sea levels across 14 tide-gauge stations with wind and wave data. The aim is to exclusively utilize meteorological information for identifying extreme sea level occurrences, thereby enhancing the prediction of such events through weather forecasting.

How to cite: Minola, L., Re, A., Bedoya-Valestt, S., Motta, C., Azorin-Molina, C., Pezzoli, A., and Chen, D.: Quantifying the impact of near-surface winds on the occurrence of extreme sea level rises along the Swedish Baltic coastline: A statistical analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3440, https://doi.org/10.5194/egusphere-egu24-3440, 2024.

10:00–10:10
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EGU24-9762
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ECS
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On-site presentation
The interannual and decadal sea level variabilities over the Indo-Pacific Oceans in the Reanalysis and CMIP6 Historical Simulations and Projections 
Ponni Maya, José Antonio Álvarez Antolínez, Deepa Js, and Chellappan Gnanaseelan

In climatological research, understanding past and accurately simulating future sea level variability is paramount due to the considerable risk that sea level changes pose to low-lying regions, coupled with their significant influence on the occurrence and severity of extreme meteorological events  . This research insights are vital in evaluating the potential impact on renewable energy sources, particularly offshore wind, wave, and tidal energy, where changes in sea level can significantly alter the efficiency and viability of these energy converters. This study comprehensively analyses sea level variability on interannual and decadal scales in the Indo-Pacific region, integrating data from the Ocean Reanalysis System 5 (ORAS5), CMIP6 historical simulations spanning from 1850-2014, and future projections under the CMIP6 future intermediate emission scenario (rcp245/ssp245) for the period 2015 to 2100. Our investigation spans key areas such as the Northwest Central Pacific Ocean (NWCPO), the Eastern Equatorial Pacific Ocean (EEPO), and the Thermocline Ridge of the Indian Ocean (TRIO), among others.
We report findings on interannual and decadal Sea Level Anomaly (SLA) variability, especially highlighting the TRIO region and various Pacific Ocean zones such as the SWPO, NWCPO, EEPO, and NWNPO. Our study identifies a substantial increase in interannual variability in the NWNPO. We also observe consistent sea-level variability patterns across these regions, extending into future projections under moderate emission scenarios.
We find that the El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole, and the Pacific Decadal Oscillation are key drivers of these variabilities. Our study reveals a strong connection between sea levels in the Equatorial Pacific and the Niño 3.4 index, suggesting its potential as a sea level-based indicator for El Niño and La Niña events.
Our research highlights the critical role of atmospheric forcing in driving sea level variability. We link high sea-level variability regions to significant wind stress curl anomalies, with distinct differences between hemispheres. We explore the mechanics of equatorial variability, emphasizing the role of equatorial Kelvin waves and local and remote Rossby waves in different oceanic regions.
Our study concludes that most CMIP6 models, despite large model uncertainty, predict an increase in sea level variability for the upcoming century, particularly in the Pacific Ocean, emphasizing the need for heightened attention to this dynamic region in the context of global climate change .

How to cite: Maya, P., Álvarez Antolínez, J. A., Js, D., and Gnanaseelan, C.: The interannual and decadal sea level variabilities over the Indo-Pacific Oceans in the Reanalysis and CMIP6 Historical Simulations and Projections, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9762, https://doi.org/10.5194/egusphere-egu24-9762, 2024.

Coffee break
Chairpersons: Carolina M.L. Camargo, Aimée Slangen
10:45–10:55
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EGU24-11869
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On-site presentation
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Relative sea level rise trends and projections up to 2150 along the Italian coasts: implications for coastal flooding 
Marco Anzidei, Antonio Vecchio, Tommaso Alberti, Enrico Serpelloni, and Anita Grezio

We focus on the current and future sea level (SL) trends along the Italian coasts which are affected by spatially variable rates of Vertical Land Movements (VLM) in response to tectonics and anthropic activities. Since VLM play a crucial role in local sea level rise along the coasts, they need to be estimated and incorporated in the analysis for more affordable sea level rise projections.

To estimate the current VLM rates we used geodetic data from about 27 years of continuous GNSS observations at a set of stations belonging to Euro-Mediterranean networks located within 5 km from the coast. Revised SL projections up to the year 2150 are provided at a set of points on a geographical grid and at the location of some tide gauges belonging to the PSMSL network, by including the estimated VLM in the SL projections released by the IPCC in the AR6 Report. Our results show that the current IPCC projections are not representative of the expected future sea levels since they do not properly consider the effects of tectonics and other local factors. Here we show that revised multi-temporal sea level projections at 2030-2050-2100 and 2150 show significant differences with respect to those of the IPCC for different Shared Socio-economic Pathways and global warming levels. Finally, our results indicate that about 1600 km of length and 10.000 km2 of the considered Italian coasts are yet exposed to flooding risk, with enhanced impacts on the environment, human activities and coastal infrastructures, in particular in 39 coastal plains. With the above scenarios, and especially in case of eventual instabilities of the Greenland and west Antarctica ice sheets, the effects of extreme meteorological events and tsunamis, will soon amplified along the Italian coasts, with serious concerns for main and small islands. Therefore, actions are needed to support vulnerable populations to adapt to the expected relative sea level rise by the end of this century and beyond.

How to cite: Anzidei, M., Vecchio, A., Alberti, T., Serpelloni, E., and Grezio, A.: Relative sea level rise trends and projections up to 2150 along the Italian coasts: implications for coastal flooding, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11869, https://doi.org/10.5194/egusphere-egu24-11869, 2024.

10:55–11:05
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EGU24-7891
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On-site presentation
Revisiting the relation between ocean heat storage and thermal expansion from a water mass perspective 
Robin Waldman, Benoît Meyssignac, Sébastien Fourest, Robin Guillaume-Castel, Karina von Schuckmann, and Jean-Baptiste Sallée

The excess anthropogenic ocean heat is causing thermal expansion, which has driven approximately 40% of the industrial-era global mean sea level rise. This relation between ocean heat uptake H and thermosteric sea level rise hθ is mediated by the so-called expansion efficiency of heat (EEH=hθ/H, in m/YJ) which characterises the expansion of a water-mass under a unit increase of its enthalpy. The EEH of a water-mass depends on its temperature, salinity and pressure. At global scale the EEH has been characterized in both historical observations and climate simulations, but the the role of regional EEH and of individual water-mass layers in the formation of this global expansion efficiency remains undocumented. Here we propose a new approach where the EEH is decomposed in temperature coordinate into a temperature plus a pressure contribution to seawater thermal expansion. We show that the temperature contribution largely dominates the global signal. We also show that the global EEH can be interpreted as a weighted global average thermal expansion coefficient.

We make use of the global EEH decomposition in temperature coordinate to estimate the contribution of individual water-mass layers to global thermal expansion in both historical reference observational datasets and Climate Model Intercomparison Project (CMIP5-6) historical and scenario simulations. Results show a contrasting picture of water mass contributions to global thermal expansion and sea level rise. Whereas ocean warming is distributed between mode, intermediate and deep waters, a disproportionate share of global ocean expansion occurs within tropical waters and subtropical mode waters. Regionally, tropical Pacific waters and subtropical north Atlantic mode waters appear as key contributors to global thermal expansion. These results show that the regional distribution of ocean heat uptake is a key driver of thermal expansion and sea level rise not only at regional scale but also at global scale. We also show that projections of future sea level rise at global scale critically depend on the ability of climate models to simulate both the regional water mass properties and their heat uptake.

How to cite: Waldman, R., Meyssignac, B., Fourest, S., Guillaume-Castel, R., von Schuckmann, K., and Sallée, J.-B.: Revisiting the relation between ocean heat storage and thermal expansion from a water mass perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7891, https://doi.org/10.5194/egusphere-egu24-7891, 2024.

11:05–11:15
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EGU24-19505
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Virtual presentation
Progress in the Global Sea Level Fingerprints since the 20th century 
Yuxin Liu, Shanshan Deng, Wenxi Zhang, and Ange Hu

Ocean mass change is the primary driver of sea level rise. Understanding the mechanisms of mass sea level change can help coastal areas scientifically respond to climate change. Under combined the self-attraction and loading effect and the Earth's rotational feedback, land-source freshwater input leads to global spatiotemporal heterogeneity of mass sea level, known as Sea Level Fingerprints. In this study, Sea Level Fingerprints were simulated under three different scenarios, covering periods from January 1901 to July 2019, January 1981 to June 2020, and July 1979 to June 2020. These scenarios encompassed: (1) consideration of climate variability alone; (2) consideration of both climate variability and actual glacial mass balance; and (3) alignment with recent climate change trends. The study aimed to analyze the contribution of Sea Level Fingerprints to satellite-derived mass sea level across these three scenarios. Results showed that in all three scenarios, the significant seasonal amplitude regions include the South China Sea and the Bay of Bengal, with peak values ranging from 42.60 to 45.20 mm. Changes in mass sea level are primarily caused by climate variability. Sea Level Fingerprints, which considered only precipitation and temperature as key indicators of climate variability, best reproduced the variation signal of the GRACE-derived data and the Altimetry-derived mass component. The spatial similarity coefficient derived between their global change range distributions were 0.67 and 0.87, respectively. Sea Level Fingerprints, which additionally considered glacial mass balance, provided a more accurate depiction of the spatial distribution and long-term trend of mass sea level derived from Altimetry satellites and Argo systems. This was demonstrated by the similarity between the sea-level fingerprints and altimetry-derived mass components across global long-term trend distribution patterns, with a spatial similarity coefficient of 0.75. The main contributing regions to these patterns include the Greenland Ice Sheet, Alaska, the Southern Andes, the Caucasus, the Middle East, and West Antarctica.

How to cite: Liu, Y., Deng, S., Zhang, W., and Hu, A.: Progress in the Global Sea Level Fingerprints since the 20th century, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19505, https://doi.org/10.5194/egusphere-egu24-19505, 2024.

Future sea-level changes
11:15–11:25
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EGU24-3503
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solicited
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Highlight
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On-site presentation
Improving, evaluating and sharing projections of global mean sea level rise 
Tamsin Edwards, Fiona Turner, and Victor Malagon Santos and the EU PROTECT project
Projections of the ice sheet and glacier contributions to sea level rise to 2100 in the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report were made by representing physical models with statistical "emulators" or machine learning techniqes (Edwards et al., 2021). This allowed estimation of the impacts of several kinds of model uncertainty on sea level projections: multiple models for the ice sheets and glaciers, multiple settings determining ice sheet sensitivity to climate change, and multiple estimates of global warming, as well as uncertainty from the emulators themselves.
 
However, there were some limitations, including: predicting each year of the century independently (i.e. not providing smooth timeseries or the possibility to assess rates of change), beginning physical model simulations in 2015 (not allowing evaluation with observations), and exploring a small number of possible model settings. Projections beyond 2100 also had to be estimated for the IPCC with other methods. These limitations presented difficulties for users.
 
We improve on these projections here in their usefulness and robustness for coastal impacts communities and decision-makers. Usefulness: by predicting ice sheet and glacier changes to 2300, not 2100; providing smooth timeseries; and incorporating the emulators into the community FACTS sea level calculation framework (Kopp et al., 2023) for use by others. Robustness: by systematically exploring many more model settings than before (including, for the first time, those for glacier models), and beginning in the past to allow calibration of the projections with observations. The result is more meaningful trajectories of sea level contribution from each land ice source, in which we have greater confidence. We combine these in FACTS with estimates of thermal expansion and land water changes to show new projections of global mean sea level rise. This work was carried out by the EU Horizon 2020 project PROTECT.
 
References:
 
Edwards et al. (2021) Projected land ice contributions to twenty-first-century sea level rise, Nature, 593, 74–82.
 
Kopp et al. (2023) The Framework for Assessing Changes To Sea-level (FACTS) v1.0: a platform for characterizing parametric and structural uncertainty in future global, relative, and extreme sea-level change, Geosci. Model Dev., 16, 7461–7489. 
 

How to cite: Edwards, T., Turner, F., and Malagon Santos, V. and the EU PROTECT project: Improving, evaluating and sharing projections of global mean sea level rise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3503, https://doi.org/10.5194/egusphere-egu24-3503, 2024.

11:25–11:35
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EGU24-10576
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ECS
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Highlight
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On-site presentation
Extreme sea-level projections along European coasts for climate adaptation services  
Maialen Irazoqui Apecechea, Angelique Melet, Guillaume Reffray, and Goneri Le Cozannet

Sea-level rise is one of the most hazardous climate-change impacts and is projected to trigger dramatic increases of coastal flooding frequency in Europe in the current century and beyond.  As such, adaptation-related effective decision making relies on the availability of authoritative and locally relevant information on future coastal sea-levels and their extremes, which include uncertainty quantification. However, current available sea-level projections are typically limited by either too low spatial resolution and therefore missing physical processes relevant at the coast, they account for only part of the sea-level signal (e.g. storm surges), and/or are typically limited to the downscaling of a single atmospheric model and therefore offer no quantification of the potentially significant inter-model uncertainty.   

In response to this knowledge gap, we present a novel extreme sea-level (ESL) projection dataset which focuses on the North-east Atlantic region. The dataset consists of a CMIP6-forced multi-model ensemble of downscaled projections until the end of the century, generated with a regional 3-dimensional ocean model at ~7km resolution. As such, the model captures not only storm-surge and tide induced ESLs, typically captured in barotropic 2-dimensional models, but also accounts for the contribution of circulation and density-driven modulations to extremes. Therefore, the ensemble dataset offers an excellent opportunity to explore ESL drivers at different spatio-temporal scales, their projected future changes, and associated uncertainties.

This dataset will help to advance scientific knowledge on climate-change induced coastal flood risk changes, but also to increase confidence in quantitative assessments of impacts of sea-level rise through its contribution to the Coastal Climate Core Service (CoCliCo), a decision-oriented platform which will inform users on present-day and future coastal risks, and which is currently under development as part of a European Union’s Horizon 2020 project.

The CoCliCo project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101003598

How to cite: Irazoqui Apecechea, M., Melet, A., Reffray, G., and Le Cozannet, G.: Extreme sea-level projections along European coasts for climate adaptation services , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10576, https://doi.org/10.5194/egusphere-egu24-10576, 2024.

11:35–11:45
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EGU24-18361
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On-site presentation
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New sea level scenarios for the Netherlands 
Sybren S. Drijfhout, Dewi Le Bars, and Iris Keizer

We present the framework used to develop a new set of sea level scenarios for the Dutch coast published by KNMI in October 2023, to help the Netherlands adapt to sea level rise. Based on interactions with stakeholders, the development of the scenarios focused on two main areas: the connection between observations and projections and the development of low-likelihood high-impact scenarios up to 2300. We developed a local sea level budget for the period 1993-2021 to better understand past observations and to constrain the scenarios. In particular, the contribution of Ocean Dynamic Sea Level was important in the benchmark period 1993-2021, and observational evidence was used to select CMIP6 models that were close to the observations. For the low-likelihood high-impact scenarios three lines of evidence were used: structured expert judgement, a numerical model including Marine Ice Cliff Instability, and a physical evidence discussion. We also discuss some practical applications of these scenarios.

How to cite: Drijfhout, S. S., Le Bars, D., and Keizer, I.: New sea level scenarios for the Netherlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18361, https://doi.org/10.5194/egusphere-egu24-18361, 2024.

11:45–11:55
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EGU24-6564
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On-site presentation
Emulating Thermosteric Sea-Level Rise Using a Three-Layer Energy Balance Model 
Víctor Malagón-Santos, Aimée Slangen, Tim Hermans, Tamsin Edwards, and Fiona Turner

Although the mass loss of land ice is projected to be the largest contribution to sea-level rise in the coming centuries, thermal expansion will also be an important contributor and its accurate projection is primordial to understanding sea-level change over (multi-)centennial timescales. Earth System Models (ESMs) are the main tools for projecting thermosteric sea-level rise. ESMs, however, are computationally demanding and therefore long, multi-centennial simulations are challenging. In this study, we use a physical-based emulator that simplifies the climate system by using three vertically stacked layers, allowing us to mimic the energy balance response of ESMs to reproduce their thermal expansion simulations. We use this emulator to extrapolate simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) from 2100 to 2300 and validate our method with CMIP6 runs that are available over that time scale. Overall, the three-layer emulator outperforms its two-layer predecessor in simulating thermal expansion up to 2300, providing a reduction of up to 78% in cumulative error for the projection period covering 2100 to 2300. Finally, we demonstrate how using temperature output from the three-layer model can help us capture non-linearities in dynamic sea-level change better than its two-layer counterpart. The latter is a first step towards building more reliable emulation approaches for oceanic processes affecting regional sea-level change.

How to cite: Malagón-Santos, V., Slangen, A., Hermans, T., Edwards, T., and Turner, F.: Emulating Thermosteric Sea-Level Rise Using a Three-Layer Energy Balance Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6564, https://doi.org/10.5194/egusphere-egu24-6564, 2024.

11:55–12:05
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EGU24-21107
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ECS
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Virtual presentation
The defining roles of sterodynamic sea level in future climate projections 
Jan-Erik Tesdal, John Krasting, Robert Kopp, Praveen Kumar, Stephen Griffies, and William Sweet

Our ability to characterize and quantify the complex uncertainties surrounding future sea-level changes is crucial for coastal risk assessments and adaptation strategies. This study focuses on the role of steric and dynamic changes (i.e., sterodynamics) in sea level projections, particularly regarding their contribution to the uncertainty of global and regional sea level changes in relation to other components such as ice sheet dynamics. A probabilistic framework is used to estimate probability distributions of sea-level change for each component. Through variance decomposition, the total uncertainty in sea-level change is dissected into its constituent sources. Subsequently, the relative contribution of sterodynamics uncertainty is quantified across various regions, time frames, emission scenarios, and projection methodologies utilized to estimate future sea-level distributions. The contribution of sterodynamics to overall uncertainty reduces over time as the contribution from ice sheets becomes more pronounced. The spatiotemporal pattern of sterodynamic significance is not strongly dependent on future greenhouse gas emissions, yet its overall role is highly dependent on the representation (e.g., emulation) of ice sheets. When high-end, low-probability estimates of future Antarctic ice sheet contributions are excluded, sterodynamics remain a dominant source of regional sea-level uncertainty at the end of this century, particularly along the US East Coast and European coast. These regions are also identified as hotspots for future sea-level rise, indicating that sterodynamic processes will play a significant role in assessing coastal vulnerabilities there. This study suggests that ocean model development can most effectively reduce the overall uncertainty in future sea-level projections by focusing on these areas.

How to cite: Tesdal, J.-E., Krasting, J., Kopp, R., Kumar, P., Griffies, S., and Sweet, W.: The defining roles of sterodynamic sea level in future climate projections, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21107, https://doi.org/10.5194/egusphere-egu24-21107, 2024.

12:05–12:15
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EGU24-4335
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ECS
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On-site presentation
Uncertainties in the projection of dynamic sea level in CMIP6 and FGOALS-g3 large ensemble 
Chenyang Jin, Hailong Liu, Pengfei Lin, and Yiwen Li

Decision-makers need reliable projections of future sea level change for risk assessment. Untangling the sources of uncertainty in sea level projections will help narrow the projection uncertainty. Here, we separate and quantify the contributions of internal variability, intermodel uncertainty, and scenario uncertainty to the ensemble spread of dynamic sea level (DSL) at both the basin and regional scales using Coupled Model Intercomparison Project Phase 6 (CMIP6) and FGOALS-g3 large ensemble (LEN) data. For basin-mean DSL projections, intermodel uncertainty is the dominant contributor (>55%) in the near- (2021-2040), mid- (2041-2060), and long-term (2081-2100) relative to the climatology of 1995-2014.  Internal variability is of secondary importance in the near- and mid-term until scenario uncertainty exceeds it in all basins except the Indian Ocean in the long-term. For regional-scale DSL projections, internal variability is the dominant contributor (60~100%) in the Pacific Ocean, Indian Ocean and western boundary of the Atlantic Ocean, while intermodel uncertainty is more important in other regions in the near-term. The contribution of internal variability (intermodel uncertainty) decreases (increases) in most regions from mid-term to long-term. Scenario uncertainty becomes important after emerging in the Southern, Pacific, and Atlantic oceans. The signal-to-noise (S/N) ratio maps for regional DSL projections show that anthropogenic DSL signals can only emerge from a few regions. Assuming that model differences are eliminated, the perfect CMIP6 ensemble can capture more anthropogenic regional DSL signals in advance. These findings will help establish future constraints on DSL projections and further improve the next generation of climate models.

How to cite: Jin, C., Liu, H., Lin, P., and Li, Y.: Uncertainties in the projection of dynamic sea level in CMIP6 and FGOALS-g3 large ensemble, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4335, https://doi.org/10.5194/egusphere-egu24-4335, 2024.

12:15–12:25
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EGU24-21090
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ECS
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On-site presentation
Fast recovery of North Atlantic sea level in response to atmospheric CO2 removal 
Sunhee Wang, Yechul Shin, Ji-Hoon Oh, and Jong-Seong Kug

Human-induced increases in atmospheric carbon dioxide (CO2) cause global warming, which leads global mean sea level rise. Previous research has shown that even with the reduction or removal of atmospheric CO2, the global mean sea level will not return to its initial level. However, the regional effects of reducing or removing atmospheric CO2 on sea level change have not been extensively studied. In this study, we analyzed global and regional sea level changes over a 560-year period, including 140 years of a linear increase in atmospheric CO2 of 1% per year, followed by 140 years of a linear decrease, and finally 280 years of maintenance at pre-industrial CO2 levels. Our analysis showed that the sea level in the North Atlantic region increased rapidly relative to the global mean, and then recovered rapidly. We attribute these variations to fluctuations in the Atlantic Meridional Overturning Circulation (AMOC). As the AMOC weakened, heat and salt were trapped in the lower latitudes of the North Atlantic region, resulting in a slower transfer of these elements to higher latitudes. As the AMOC recovered and overshoot, the accumulated heat and salt were rapidly transferred to higher latitudes, resulting in changes in sea level. Our results suggest that the North Atlantic region is more sensitive to changes in atmospheric CO2 compared to the global mean. The North Atlantic region has a high population density and is expected to suffer significant damage as a result of sea level change. Therefore, continuous research on sea level change in this region is needed, and our study could help improve the ability to predict future sea level change in this area.

How to cite: Wang, S., Shin, Y., Oh, J.-H., and Kug, J.-S.: Fast recovery of North Atlantic sea level in response to atmospheric CO2 removal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21090, https://doi.org/10.5194/egusphere-egu24-21090, 2024.

Posters on site: Thu, 18 Apr, 16:15–18:00 | Hall X5

Display time: Thu, 18 Apr, 14:00–Thu, 18 Apr, 18:00
Chairpersons: Carolina M.L. Camargo, Aimée Slangen
Past sea-level changes
X5.163
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EGU24-488
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ECS
Last Interglacial sea level derived from U-series dated fossil corals of the Turks and Caicos Islands
(withdrawn)
Oana Dumitru, Blake Dyer, Jacqueline Austermann, William D'Andrea, Roger Creel, Louise Bolge, Steven Goldstein, and Maureen Raymo
X5.164
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EGU24-14249
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ECS
Mid-Holocene relative sea-level reconstruction from digital surface models of coral microatolls at Pulau Semakau, southwestern Singapore  
Lin Thu Aung, Nural Syafiqah Tan, Jennifer Susan Quye-Sawyer, Fangyi Tab, Junki Komori, Zihan Aw, Jing Ying Yeo, Wan Lin Neo, Maya Baltz, and Aron Maltzner

Coral microatolls are coral colonies that grow with distinct morphologies consisting of living polyps on their outer perimeters and dead upper surfaces with concentric rings in planform. Their upward growth is limited by the lowest tides, allowing them to be used as precise indicators of relative sea-level (RSL) change. Therefore, detailed morphological investigation of fossil microatolls provides an important proxy for the reconstruction of past RSL. We present a preliminary RSL reconstruction from Pulau Semakau (Semakau Island), southwestern Singapore, based on digital surface models (DSMs) of fossil corals captured by portable iPhone LiDAR integrated with field survey data and radiocarbon analysis. Pulau Semakau is the largest field site in Singapore, with an intertidal flat extending more than 2 km long by 0.4 km wide, on which we observed 79 living and 65 fossil microatolls containing well preserved, concentric rings. In this study, we reconstruct mid-Holocene RSL using seven fossil, Diploastrea heliopora microatolls, relative to living counterparts on the island. DSMs indicate that three of these fossil corals are lower in elevation at the center with higher outer rings, indicating gradual RSL rise between ~7700 and 7500 cal yr BP. Conversely, three fossil corals are observed to decrease in elevation from the innermost to outermost rings, indicative of RSL fall between ~7350 and 7200 cal yr BP. These observations are consistent with but more well constrained than the existing sea-level curve of Singapore based on sea-level index points (SLIPs) and limiting dates from intertidal mangrove and shallow marine sediments. RSL records between ~7500 and 7350 cal yr BP are largely uncertain due to erosion of a fossil coral, and this remains as future work. The initial results reflect mid-Holocene RSL fluctuations at Pulau Semakau, from ~7700 to 7200 cal yr BP.

How to cite: Aung, L. T., Tan, N. S., Quye-Sawyer, J. S., Tab, F., Komori, J., Aw, Z., Yeo, J. Y., Neo, W. L., Baltz, M., and Maltzner, A.: Mid-Holocene relative sea-level reconstruction from digital surface models of coral microatolls at Pulau Semakau, southwestern Singapore , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14249, https://doi.org/10.5194/egusphere-egu24-14249, 2024.

X5.165
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EGU24-5258
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ECS
Drivers of Common Era sea-level change in southeastern Australia: extending tide-gauge records and developing a network of high-resolution reconstructions for regional analyses. 
Sophie Williams, Rafael Carvalho, Prudence Perry, Ruth Reef, and Juliet Sefton

Southern Hemisphere observational records of sea-level change are rare prior to ~1950, making it difficult to close historical regional sea-level budgets and quantify individual contributions to sea level (e.g. barystatic, thermosteric). Recent work generated four microfossil-based high-resolution sea-level reconstructions from southeastern Australia, all of which indicated rapid regional rates of 20th century sea-level rise compared to the global average. However, unlike analogous work in the North Atlantic (for which there is a high-density network of high-resolution reconstructions), there remains a paucity of proxy data from the Southern Hemisphere, hindering a probabilistic estimate of regional drivers of relative sea level using a spatio-temporal model.

We generate two new reconstructions using salt-marsh foraminifera from King Island, Tasmania, and Venus Bay, Victoria, to add to a growing database of Common Era sea-level reconstructions from southeastern Australia (and indeed wider Australasia). Fossil foraminifera indicate a rising palaeomarsh over the last ~150 years of ~0.15-0.25 m (average); this is interpreted as relative sea-level rise consistent with patterns observed in recent reconstructions. A chronology for the core is developed using both 14C and lead isotopes. Ongoing efforts to supplement the regional database will allow us to determine local and regional drivers of relative sea-level change in the region.

How to cite: Williams, S., Carvalho, R., Perry, P., Reef, R., and Sefton, J.: Drivers of Common Era sea-level change in southeastern Australia: extending tide-gauge records and developing a network of high-resolution reconstructions for regional analyses., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5258, https://doi.org/10.5194/egusphere-egu24-5258, 2024.

X5.166
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EGU24-15948
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ECS
Drivers of Late Holocene relative sea-level change in the Sunda Shelf: new insights from coral microatolls in Singapore 
Fangyi Tan, Benjamin Horton, Ke Lin, Tanghua Li, Maeve Upton, Yucheng Lin, Jennifer Walker, Trina Ng, Jennifer Quye-Sawyer, Joanne TY Lim, Shi Jun Wee, Nurul Syafiqah Tan, and Aron Meltzner

Existing Late Holocene relative sea-level (RSL) records from the Sunda Shelf suffer from spatial and temporal discontinuities and/or a lack of precision, hindering an understanding of the drivers of RSL change. Here, we present the first RSL record from fossil coral microatolls in Singapore, which has high vertical (<± 0.20 m, 2𝜎) and temporal (<± 26 yrs, 95% highest density region) precision.

We applied a novel approach to produce sea-level index points and infer sea-level tendencies by combining (1) the use of photogrammetry with traditional levelling techniques; (2) 230Th dating; and (3) surface morphologies of the fossil coral microatolls. The fossil corals reveal a gradual, 0.31 ± 0.18 m (2𝜎) fall in RSL between 2.8 kyrs BP and 0.6 kyrs BP, with rates averaging 0.15 ± 0.10 mm/yr (2𝜎). Our coral record lies within uncertainty of some of the published RSL records from the region but disagrees with others, suggesting that local to regional processes may be driving spatial variability in RSL in the region. Misfits of the data with glacial isostatic adjustment (GIA) models may be explained by the influence of non-GIA processes, such as vertical land motion, and/or the need to fine-tune GIA model parameters. Work is ongoing to decompose the drivers of relative sea-level change within the region.

How to cite: Tan, F., Horton, B., Lin, K., Li, T., Upton, M., Lin, Y., Walker, J., Ng, T., Quye-Sawyer, J., Lim, J. T., Wee, S. J., Tan, N. S., and Meltzner, A.: Drivers of Late Holocene relative sea-level change in the Sunda Shelf: new insights from coral microatolls in Singapore, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15948, https://doi.org/10.5194/egusphere-egu24-15948, 2024.

X5.167
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EGU24-16146
Spatially variable sea level response to erosion and deposition in Aotearoa New Zealand 
Gregory Ruetenik, John D. Jansen, and Ken L. Ferrier

Surface processes alter sea level by warping Earth’s surface and modifying the gravitational field. Recent studies show that paleo-sea level indicators are depressed by sedimentation near major depocenters, such as the Mississippi and Indus deltas, and raised by the erosion of rock in rapidly eroding coastal regions such as Taiwan. The South Island of Aotearoa New Zealand poses an interesting combination of these endmembers because the Southern Alps are eroding rapidly on the west coast, while high sediment loads are deposited along the eastern margin. Here, we use a global, gravitationally self-consistent sea-level model to demonstrate that sediment redistribution on the South Island drastically alters interpretations of sea level change since the Last Interglacial (Marine Isotope Stage 5e) by as much as +100 m on the west coast and –30 m on the east coast. The influence of sediment redistribution on sea level is highly sensitive to geodynamic properties such as effective elastic thickness, which we reconcile using the abundance of paleo-shoreline markers available.

How to cite: Ruetenik, G., Jansen, J. D., and Ferrier, K. L.: Spatially variable sea level response to erosion and deposition in Aotearoa New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16146, https://doi.org/10.5194/egusphere-egu24-16146, 2024.

X5.168
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EGU24-16743
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ECS
Inferring climatic sea-level variations from microatolls in tectonically active regions 
Sophie Debaecker, Mikhail Karpytchev, Mélanie Becker, Nathalie Feuillet, and Kenji Satake

Coral microatolls are often used to reconstruct the relative sea-level (RSL) along tropical coastlines. They grow at a constant rate, developing each year a growth band that can be observed in their internal stratigraphy. As their development is limited by the water height, they record annual variations of the relative sea-level once they have reached the sea surface. These changes are related to both climate and tectonic, and several criteria are used to decipher both signals. For example, it is commonly accepted that a local signal would rather correspond to a tectonic event, and inversely. However, majority of the criteria such as regrowth of the coral, amplitude of the RSL anomaly or matches with seismic or climatic events catalogs are mainly qualitative and most of the time, incomplete. In our study, we seek to develop a mathematically sound method to separate the climatic signal recorded by a series of microatolls. We focused on the region of the Ryukyus islands in south-west Japan, where the Philippine sea plate plunges under the Eurasia plate. In this area, up to 15 modern and living corals have been collected previously; and their RSL records extend from 1762 to 2018. They extend over 900 km along the subduction zone. Despite the seismic activity of the area, it is possible to infer that any signal common to all microatolls can be considered as climatic. We used a statistical method over the corals dataset to extract a common-mode RSL signal over the island arc. We found a long term sea-level rise for the last 200 years. We further analyze shorter time trends and annual anomalies, and compare our results from the RSL records that include years where only minimum RSL was recorded. Additionally, to refine our method we aim to compare sea level changes recorded by tide gauge in the Ryukyus with the estimates from inferred from the coral microatolls from seismically stable regions in the Pacific Ocean.

How to cite: Debaecker, S., Karpytchev, M., Becker, M., Feuillet, N., and Satake, K.: Inferring climatic sea-level variations from microatolls in tectonically active regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16743, https://doi.org/10.5194/egusphere-egu24-16743, 2024.

X5.169
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EGU24-3445
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ECS
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Are multi-decadal sea-level oscillations augmenting rates of mean sea level? 
Erin Robson, Luke Jackson, and Sophie Williams

There is evidence to show sea-level change is accelerating, with a departure from Holocene rates in the late-19th century, to more than a doubling of the rate of global mean sea-level change over the past 25-years. Although the effect of anthropogenic forcing on sea level is certain, the influence of natural internal variability on augmenting rates of change remains an important area of research. This is especially significant at ocean-climate response timescales (>30-years). Using tide-gauge data, we apply empirical mode decomposition (EMD) to separate both the global and regional sea-level records into a series of intrinsic mode functions (IMFs) that are quasi-periodic in character. From them, we identify the dominant modes of variability that are common to each ocean basin, and compare these to recognised modes of climate variability to determine the causal factors of sea-level oscillations. We also conduct a sensitivity analysis with sub-sampled tide-gauge data to test the feasibility of this approach with high-resolution proxy-based sea-level reconstructions.

How to cite: Robson, E., Jackson, L., and Williams, S.: Are multi-decadal sea-level oscillations augmenting rates of mean sea level?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3445, https://doi.org/10.5194/egusphere-egu24-3445, 2024.

X5.170
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EGU24-19740
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ECS
Observation of Nonseismic Sea level Oscillations at TsunamiTimescales (T < 2 hours) along the Indian Subcontinent
(withdrawn after no-show)
Balakrishnan Rohith, Sudheer Sidharth, and Nambiathody Anup
X5.171
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EGU24-9936
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ECS
Linking the Permanent Service for Mean Sea Level’s (PSMSL) global mean sea level dataset to the ellipsoid  
Chanmi Kim, Andrew Matthews, and Elizabeth Bradshaw

The Permanent Service for Mean Sea Level (PSMSL) is the internationally recognised global sea level data bank for long term sea level change information from tide gauges, responsible for the collection, publication, analysis and interpretation of sea level data. The PSMSL was founded 90 years ago, and today operates from the Liverpool site of the UK’s National Oceanography Centre. 

The PSMSL’s main product, a dataset of monthly and annual means from over 2000 locations worldwide aggregated from over 200 suppliers, is a cornerstone in our understanding of changes in sea level over the two centuries. For our highest quality Revised Local Reference (RLR) dataset, we ensure the data can all be referred to a fixed point on land, ensuring a consistent vertical reference frame is used throughout the record. Also, we provide GNSS solutions near the guage to estimate the ellipsoidal height and rate of movement of the site in our website.

Here we introduce the PSMSL mean sea level dataset, and explain how we present these ellipsoidal ties on our website. We also discuss ongoing efforts to improve the breadth of metadata we supply, and attempts to ensure they meet FAIR data practices (Findable, Accessible, Interoperable and Reusable). 

 

How to cite: Kim, C., Matthews, A., and Bradshaw, E.: Linking the Permanent Service for Mean Sea Level’s (PSMSL) global mean sea level dataset to the ellipsoid , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9936, https://doi.org/10.5194/egusphere-egu24-9936, 2024.

X5.172
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EGU24-2288
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Recent Sea Level Rise and Variability in Singapore Region Derived from Tide Gauges and Satellite Altimetry 
Pavel Tkalich and Quang-Hung Luu

Sea level in the Southeast Asia (SEA) seas is driven by various phenomena at global,  regional and local scales. The latest tide gauge and satellite data revealed its most recent spatial and temporal patterns. The trend of global sea level rise in Singapore region is hindered by dominant variability of El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Indian Ocean Dipole (IOD), as well as associated modulation of Asian Monsoon. It was confirmed that positive sea-level anomalies in the southern and western areas of Southeast Asia seas were significantly high (~10 cm) during the northeast monsoon, especially in the Gulf of Thailand (~25 cm). The sea level trends for these regions were basically reversed during the southwest monsoon but with a smaller magnitude of negative sea-level anomalies. The regional sea-level trend in the Sunda Shelf differed from region to region, with the rates varied greatly from 1.4 to more than 4.8 mm/year. Interestingly, the rates on the east-western side of the region were roughly 3.0-4.5 mm/year, which were higher than the ones at other regions, being 2.5-3.5 mm/year. The presentation discuss the causes and consequences of sea level rise and variability in SEA and Singapore region in particular.

This Research is supported by Singapore’s National Research Foundation and National Environment Agency under the National Sea Level Programme Funding Initiative (Award No. USS-IF-2020-4).

How to cite: Tkalich, P. and Luu, Q.-H.: Recent Sea Level Rise and Variability in Singapore Region Derived from Tide Gauges and Satellite Altimetry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2288, https://doi.org/10.5194/egusphere-egu24-2288, 2024.

X5.173
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EGU24-10137
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ECS
Reconstruction of the global ocean heat content and thermosteric sea-level rise with an improved configuration of the ISAS interpolation tool 
Rémy Asselot, Nicolas Kolodziejczyk, William Llovel, Kevin Balem, and Annaïg Prigent-Mazella

Anthropogenic greenhouse gas emissions have caused an imbalance in the energy content of the Earth's system, warming the atmosphere, the land surface, the cryosphere and the ocean. On a global scale, over the last five decades, the ocean has stored more than 90% of the heat excess associated with the Earth energy imbalance. This absorption of heat by the ocean leads to an increased Oceanic Heat Content (OHC). As the OHC rises, the global mean sea-level increases due to thermal expansion, a mechanism known as the global mean thermosteric sea-level (TSL) rise. In order to monitor accurately the global OHC and global mean TSL, one of the main sources of data is in situ Temperature and Salinity profiles. These profiles need to be interpolated on a regular grid to prevent any bias due to regional over or under-sampling. However, to date, OHC and TSL estimates and their associated uncertainties are sensitive to the parameterization and a priori assumption of the interpolation tools. To address this issue in a controlled framework, we run sensitive experiments where we adjust the configuration of the In Situ Analysis System (ISAS) interpolation tool. To do so, we extracted “synthetic profiles” of Temperature and Salinity from NEMO simulations, integrated over the 1980-2020 period.  We interpolated these profiles with ISAS and compared them with the original model outputs. This comparison allows us to improve the parameterization and a priori assumption of ISAS in order to, ultimately, provide a better understanding of the sensitivity of the global and regional OHC and TSL estimates. Here we present the first results of this work.

How to cite: Asselot, R., Kolodziejczyk, N., Llovel, W., Balem, K., and Prigent-Mazella, A.: Reconstruction of the global ocean heat content and thermosteric sea-level rise with an improved configuration of the ISAS interpolation tool, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10137, https://doi.org/10.5194/egusphere-egu24-10137, 2024.

X5.174
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EGU24-19452
The barystatic contribution to multi-decadal sea-level change in the 19th century. 
Luke Jackson, Sophie Williams, Fiona Hibbert, Sönke Dangendorf, Ed Garrett, Andrew Sole, and Roland Gehrels

Understanding long-term trends in mass loss is vital for assessing the (in)stability of ice sheets and glaciers and their subsequent contribution to global mean sea level. Observational estimates of mass loss from the Greenland and Antarctic Ice Sheets are scarce before the satellite era (i.e., 1990s), and from glaciers before the 1950s. A variety of modelling techniques (process-driven and statistical) have been employed to synthesise and extend observational estimates, so that much of the 20th century sea-level budget is closed within uncertainty. Despite this work, uncertainty remains, particularly for contributions prior to ~1940 and the 19th century. 

Sea-level fingerprinting exploits the fact that the geometry of land-based water masses (i.e., ice sheets, glaciers, hydrological storage) and any changes (via loss or gain) will generate a unique gravitational equipotential surface (fingerprint). We apply this technique in a Monte-Carlo-based linear inversion model to isolate the globally averaged barystatic contribution from Greenland, Antarctica and glaciers over pentadal periods since 1813. We use a selection of long-duration tide gauges and high-resolution proxy-based sea-level reconstructions, with model-based glacio-isostatic adjustment (GIA), stero-dynamic, and terrestrial water storage corrections. 

Our initial findings confirm the validity of the approach when comparing barystatic contributions to observed estimates for the last 50 years. Whilst uncertainty is significant for the 19th century, the barystatic contribution deviates from zero in different pentads. We also conduct a sensitivity analysis to evaluate the idealised locations/corrections required to enhance confidence in the inversion procedure.

How to cite: Jackson, L., Williams, S., Hibbert, F., Dangendorf, S., Garrett, E., Sole, A., and Gehrels, R.: The barystatic contribution to multi-decadal sea-level change in the 19th century., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19452, https://doi.org/10.5194/egusphere-egu24-19452, 2024.

X5.175
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EGU24-13354
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ECS
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GravIS Portal: User-friendly Ocean Bottom Pressure data from GRACE and GRACE-FO 
Christoph Dahle, Eva Boergens, Henryk Dobslaw, Ingo Sasgen, Thorben Döhne, Sven Reißland, and Frank Flechtner

The German Research Centre for Geosciences (GFZ), together with the Alfred-Wegener-Institute (AWI) and the Technische Universität Dresden, maintains the ‘Gravity Information Service’ portal (GravIS, gravis.gfz-potsdam.de). GravIS facilitates the dissemination of user-friendly data of mass variations in the Earth system, based on observations of the US-German satellite missions GRACE (Gravity Recovery and Climate Experiment, 2002-2017) and its successor GRACE-FO (GRACE Follow-On, since 2018).

The portal provides ocean bottom pressure (OBP) data on a global 1° grid. Two versions of the product are provided, based on spherical harmonic coefficients taken from either the most recent GRACE/GRACE-FO release from GFZ or from the International Combination Service for Time-variable Gravity Fields (COST-G). Corrections applied to the data include the insertion of estimates of the geocentre motion, replacement of the C20 and C30 coefficients, corrections of the co- and postseismic deformations after the three megathrust earthquakes (Sumatra-Andaman 2004, Chile 2010, Japan-Tohoku 2011), and the correction for glacial isostatic adjustment with the ICE-6G model.

The data product consists of barystatic sea-level pressures calculated from the gravity data using the sea-level equation. Residual ocean circulation is provided as well. Besides the gridded products, regional average time series are also available for predefined ocean regions.

In addition to the OBP data, GravIS provides terrestrial water storage (TWS) variations over the continents and ice mass variations over Greenland and Antarctica. These data sets are also provided either as grids or regional averages.

The data sets of all Earth system domains can be interactively displayed within the portal and are freely available for download. This contribution aims to show the features of the GravIS portal and its potential benefit to sea-level and ocean science applications.

How to cite: Dahle, C., Boergens, E., Dobslaw, H., Sasgen, I., Döhne, T., Reißland, S., and Flechtner, F.: GravIS Portal: User-friendly Ocean Bottom Pressure data from GRACE and GRACE-FO, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13354, https://doi.org/10.5194/egusphere-egu24-13354, 2024.

Future sea-level changes
X5.176
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EGU24-15877
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ECS
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Highlight
Regional variations in relative sea level changes influenced by non-linear vertical land motion  
Julius Oelsmann, Marta Marcos, Marcello Passaro, Laura Sanchez, Denise Dettmering, Sönke Dangendorf, and Florian Seitz

Vertical land movements can cause regional relative sea level changes to differ substantially from climate-driven absolute sea level changes. While absolute sea level has been accurately monitored by satellite altimetry since 1992, there are limited observations of vertical land motion. Vertical land motion is generally modeled as a linear process, despite some evidence of non-linear motion associated with tectonic activity, changes in surface loading, or groundwater extraction. As a result, the temporal evolution of vertical land motion, and its contribution to projected sea level rise and its uncertainty, remains unresolved. Here, we present a probabilistic vertical land motion reconstruction from 1995-2020 and determine the impact of regional scale and non-linear vertical land motion on relative sea level projections up to 2150. We show that regional variations in projected coastal sea level changes are equally influenced by vertical land motion and climate-driven processes, with vertical land motion causing relative sea level changes of up to 50 cm by 2150. Accounting for non-linear vertical land motion increases the uncertainty in projections by up to 1 m on a regional scale. Our results highlight the uncertainty in future coastal impacts and demonstrate the importance of including non-linear vertical land motions in sea level change projections. In addition to its application to regional sea level projections, the vertical land motion estimate is an important source of information for various sea level studies focusing on the analysis of tide gauge or satellite altimetry observations in coastal areas.

How to cite: Oelsmann, J., Marcos, M., Passaro, M., Sanchez, L., Dettmering, D., Dangendorf, S., and Seitz, F.: Regional variations in relative sea level changes influenced by non-linear vertical land motion , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15877, https://doi.org/10.5194/egusphere-egu24-15877, 2024.

X5.177
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EGU24-6921
Modelling dependence between the ice-sheet components of sea-level rise 
Benjamin S. Grandey, Justin Dauwels, Svetlana Jevrejeva, Antony J. Payne, Zhi Yang Koh, Benjamin P. Horton, and Lock Yue Chew

Sea-level projections are sensitive to statistical dependence between the East Antarctic, West Antarctic, and Greenland ice-sheet components.  The dependence is produced by climate uncertainty and ice-sheet process uncertainty.  To investigate this dependence, we model the dependence using copulas.  We use a vine copula to couple the ice-sheet components of projected sea level in 2100 under the SSP5-8.5 scenario.  Assumptions about rank correlation and copula family influence both the centre and the tails of the total ice-sheet contribution.  For example, rank correlation can influence the 95th percentile by approximately 50%.  We explore three alternative approaches for specifying the dependence: shared dependence on global-mean surface temperature, dependence derived from ice-sheet model ensembles, and dependence derived from expert judgement.  Shared dependence on global-mean surface temperature produces little dependence between the ice-sheet components.  In contrast, ice-sheet model ensembles suggest that the dependence between the East and West Antarctic ice-sheet components may be strong, amplifying the uncertainty in future sea-level rise.

How to cite: Grandey, B. S., Dauwels, J., Jevrejeva, S., Payne, A. J., Koh, Z. Y., Horton, B. P., and Chew, L. Y.: Modelling dependence between the ice-sheet components of sea-level rise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6921, https://doi.org/10.5194/egusphere-egu24-6921, 2024.

X5.178
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EGU24-8462
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ECS
Eddy variability contribution to decadal regional sea level trends 
Benoit Laurent, William Llovel, Anne-Marie Treguier, and Antoine Hochet

Sea level rise is one of the most direct consequences of the actual global warming. Over the 20th century, global mean sea level rises at a rate of 1.5-2 mm. yr-1. Since the beginning of the 1990s, satellite altimetry measure the changes of sea level with a near global coverage (from 66oS to 75oN). The use of satellite altimetry has, for the first time, highlighted large regional variability in sea level trends that significantly differ from the global mean estimate. If global ocean warming and land ice melting (mountain glaciers and ice sheets from Greenland and Antarctica) are the main processes explaining the observed global mean sea level rise, at regional scales, other processes are involved, such as changes in salinity or temperature associated with ocean circulation or air-sea fluxes at the ocean surface.

 

Sea level projections used in IPCC reports are based primarily on coarse-resolution coupled climate models. Current projections are based on climate models in which ocean-eddy variabilities are parameterized and results deviate from observations especially in the Southern Ocean. Mesoscale processes transport heat/freshwater over very large distances in the ocean (both horizontally and vertically). They also regulate energy, moisture and carbon exchanges between the oceans and the atmosphere via coupling. Understanding these processes and how they might change in the future is critical for portraying robust regional sea level change.

 

Recently, new generations of climate models have been integrated at spatial resolutions of ¼° and 1/12°, which is sufficient to partially resolve the mesoscale eddy variability. These higher resolutions enable the study of the impact of mesoscale eddies on regional sea level changes and how these processes may change in the future.

 

In this work, we will take advantage of a suite of climate model simulations based on HadGEM3-GC3.1 at different spatial resolution (1°, ¼° and 1/12°) to assess the contribution of eddy-variability on regional sea level trends. We first present the ability of such climate models to reproduce regional sea level trends observed by satellite altimetry over decadal to multi-decadal time periods. Second, temperature and salt budget will be presented to quantify the contribution of eddy variability on these regional sea level trends.

How to cite: Laurent, B., Llovel, W., Treguier, A.-M., and Hochet, A.: Eddy variability contribution to decadal regional sea level trends, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8462, https://doi.org/10.5194/egusphere-egu24-8462, 2024.

X5.179
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EGU24-18693
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ECS
Loss of safe land on atolls highlights need for immediate emissions reductions to support coastal adaptation 
Tessa Möller, Rosanne Martyr-Koller, Scott Kulp, Tabea Lissner, Benjamin H Strauss, Zebedee Nicholls, and Alexander Nauels

The impacts of climate change and sea level rise are posing substantial threats to the long-term habitability of low-lying atolls. As of today, the sparse data coverage of these islands limits the ability to assess and respond to climate change related risks.

Advances in coastal digital elevation models provide data for very remote coastal regions with low vertical bias. Here, we combine the Intergovernmental Panel on Climate Change regional sea level rise projections under its illustrative emissions scenarios, with the coastal digital elevation model CoastalDEM and COAST-RP, a dataset of storm tide return periods to assess the exposure to rising sea levels and coastal flooding of 166 atolls. Our results show that in 2050 and under a very low emissions scenario (SSP1-1.9), atoll area exposure to SLR and coastal flooding will amount to 35% [34-36%] and that only 64% of atoll area can still be considered safe. By the end of century and under the same scenario, only 61% can be considered safe. Under an intermediate emissions scenario (SSP2-4.5), a scenario roughly capturing projected warming under current policies and actions, the share of safe land further reduces to 58% by 2100. By 2150, only 58% or 51% of the land can still be considered safe under the very low and intermediate emissions scenario respectively. Our results show that the habitability of atolls is already threatened in the near future, but that near-term mitigation can limit the pace at which atolls are flooded in particular beyond 2100. Our results imply that in addition to immediate and rapid emission reductions in line with the Paris Agreement, remaining adaptation options must be enabled and implemented today to reduce the future exposure of atolls.

How to cite: Möller, T., Martyr-Koller, R., Kulp, S., Lissner, T., Strauss, B. H., Nicholls, Z., and Nauels, A.: Loss of safe land on atolls highlights need for immediate emissions reductions to support coastal adaptation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18693, https://doi.org/10.5194/egusphere-egu24-18693, 2024.

X5.180
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EGU24-14926
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ECS
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Sea level projections for the German Coast 
Corinna Jensen, Frank Janssen, Jens Möller, and Tim Kruschke

Sea level rise is a certain consequence and one of the most important threats associated with climate change. It increases the risk of flooding of low-lying land at the German Coast.

In cooperation of the “Network of Experts” of the German Federal Ministry for Digital and Transport and the DAS core service “climate and water”, we aim to provide high-quality projections of relative sea level change for the German coastal areas, both in terms of spatial data as well as time series for specific stations. Most of the drivers for sea level change must be considered on a continental or global scale. The main exception for this in northern Europe is land uplift as its impacts are regional and dependent on glacial isostatic adjustment as well as local processes. We therefore created a new set of sea level projections for the North Sea and Baltic Region. This dataset is based on the IPCC 6th Assessment Report (AR6) projections of absolute sea level change, which we combine with a new and high-resolution land elevation model over Fennoscandia (instead of the coarse land elevation model for this region used in the IPCC AR6). The data will eventually be published via the “DAS core service”.

 

How to cite: Jensen, C., Janssen, F., Möller, J., and Kruschke, T.: Sea level projections for the German Coast, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14926, https://doi.org/10.5194/egusphere-egu24-14926, 2024.

X5.181
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EGU24-16387
Sea-level scenarios for coastal adaptation: the example of France 
Rémi Thiéblemont and Gonéri Le Cozannet

Climate change scenarios are a typical request of adaptation practioners. Within its third national adaptation plan, France is developing a consistent set of climate scenarios based on global warming levels. The scenario currently under consideration would lead to a global mean temperature increase of 3°C with respect to the preindustrial period, which is consistent with the current climate policies to 2100. Later on, these scenarios would be integrated in the regulation, for example in order to update risk assessment guidance.

Here, we present how sea-level rise scenarios aligned with this global warming level were produced. We selected emulated simulations for each component of future sea-level rise consistently, including ocean and ice components, following a method similar to that of the 6th assessment report of the IPCC, yet with specific attention to the consistency of uncertainty treatment before and after 2100. This responds to the needs to consider impacts of sea-level rise over hundred years, that is, to 2125 within coastal risk prevention plans. Furthermore, we added simulations considering a potential collapse of ice-sheets at 3°C of global warming levels in 2100. We consider only vertical land motions related to the Glacial Isostatic Adjustment as new observations from the Copernicus Land Motion service are now available for local stakeholder’s use.

The results show that the 87th percentile of projections is close to 80cm in 2100 with respect to 1995-2014 for the majority of mainland and overseas French regions, whether ice-sheets collapse is considered or not. Conversely, median values display differences of about 10cm depending whether ice sheet collapse is hypothesized or not. In the context of the development of these new scenarios, simplicity was considered a key criterion of success to ensure that all users - and not only those with high climate literacy - can effectively use scenarios. Hence, we propose to use one single scenario corresponding to the 87th percentile of the projections. This corresponds to a cautious approach consistent with the risk prevention policy in France. This does not preclude advanced users considering additional scenarios such as low-likelihood/high-impact scenarios voluntarily.

This work was performed within a project supported by the ministry in charge of Environment. We thank the steering and scientific committees of this project for useful comments and inputs.

How to cite: Thiéblemont, R. and Le Cozannet, G.: Sea-level scenarios for coastal adaptation: the example of France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16387, https://doi.org/10.5194/egusphere-egu24-16387, 2024.

X5.182
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EGU24-17955
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ECS
Sea-level storylines to inform coastal adaptation planning and decision-making for the UK, South Africa and Southeast Asia 
Jennifer Weeks, Matthew D. Palmer, Benjamin P. Horton, Trina Ng, Susan M. Parnell, and Antony Payne

Implementing responses to sea-level rise requires accessible, credible and relevant sea-level information to facilitate effective use by practitioners and decision-makers. However, recent consultations have highlighted the need to better translate sea-level information to meet the physical and cultural diversity of decision-making and planning across the world. This includes communicating sea-level rise across a range of timescales, providing information tailored to different risk tolerances and better linking sea-level rise to impacts analysis to provide useful and usable metrics (e.g., Weeks et al., 2023, Environ. Res. Commun.). 


The presence of ambiguity in sea-level projections means there are limitations in the use of probabilistic approaches in coastal planning and decision-making (Kopp et al., 2023, Nature Climate Change). Storylines (physically consistent and plausible pathways of future climate events) are increasingly being used as a distillation tool presented alongside probabilistic sea level projections, for example to address the challenge of “deep uncertainty” associated with the future response of the ice sheets. Here, we focus on the regionalisation of sea-level projections into a set of discrete, actionable future pathways, to meet the needs of coastal adaptation planners and decision-makers. Building on the work of Palmer et al., (2020) (Earth’s Future), we generate a set of sea-level storylines for coastal city locations in the UK, South Africa and Southeast Asia, constrained by different emissions scenarios and high-end sea-level rise estimates. Locations are chosen based on their population density and geographical spread, whilst the regions allow consideration of the different risk profiles and contexts for decision-making. This work explores a range of decision-making contexts and how the storyline framework can be tailored to different user needs. 

How to cite: Weeks, J., Palmer, M. D., Horton, B. P., Ng, T., Parnell, S. M., and Payne, A.: Sea-level storylines to inform coastal adaptation planning and decision-making for the UK, South Africa and Southeast Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17955, https://doi.org/10.5194/egusphere-egu24-17955, 2024.

X5.183
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EGU24-10716
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Highlight
Exploring multi-century sea level rise commitments from 21st century cumulative emissions to inform minimum coastal adaptation needs 
Alexander Nauels, Zebedee Nicholls, Uta Klönne, Tim Hermans, Matthias Mengel, Christopher J. Smith, and Matthew D. Palmer

It is crucial to explore multi-century sea level responses under different emissions scenarios despite underlying physical uncertainties that rapidly increase over time, because resulting coastal risks fully manifest only on these longer timescales. Here, we use a set of climate and sea level emulators to investigate sea level rise commitments out to 2300 for cumulative emission levels at the start of every remaining 21st century decade under the five illustrative SSP-RCP scenarios. Our results indicate that emissions until 2030 “lock in” around 1.0 m (66% model range: 0.8 to 1.3 m) of global mean sea level rise in 2300 relative to 1995-2014. Under an intermediate emissions scenario roughly in line with current climate policies (SSP2-4.5), median 2300 global mean sea level commitments for cumulative emissions in 2050 (1.2 m) and 2100 (1.7 m) would be around 0.1 m and 0.6 m higher than under a very low emissions scenario (SSP1-1.9). Global results are also downscaled to selected regional sites and highlight that particularly vulnerable regions like low-lying Pacific Islands will experience higher local committed sea level rise than the global average. By attributing projected sea level rise commitments in 2300 to different cumulative emission levels in the 21st century, the study aims to more clearly link mitigation efforts in the near term to longer term coastal risk and to inform minimum adaptation requirements under different climate futures.

How to cite: Nauels, A., Nicholls, Z., Klönne, U., Hermans, T., Mengel, M., Smith, C. J., and Palmer, M. D.: Exploring multi-century sea level rise commitments from 21st century cumulative emissions to inform minimum coastal adaptation needs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10716, https://doi.org/10.5194/egusphere-egu24-10716, 2024.

X5.184
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EGU24-9008
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Sea-level projections in recent IPCC reports: how we got here, where we are and where we’re going  
Aimée Slangen, Matthew Palmer, Carolina Camargo, John Church, Tamsin Edwards, Tim Hermans, Helene Hewitt, Gregory Garner, Jonathan Gregory, Robert Kopp, Victor Malagon Santos, and Roderik van de Wal

Sea-level science has seen many recent developments in observations and modelling of the different contributions and the total mean sea-level change. Here, we focus on sea-level projections in the recent IPCC reports, and discuss (1) the evolution in IPCC projections (“how we got here”), (2) how the projections compare to observations (“where we are”) and (3) the outlook for further improving projections (“where we’re going”). We start by discussing how the model projections of 21st century sea-level change have changed from the IPCC AR5 report (2013) to SROCC (2019) and AR6 (2021), highlighting similarities and differences in the methodologies and comparing the global mean and regional projections. This shows that there is good agreement in the median values, but also highlights some differences. In addition, we discuss how the different reports included high-end projections. We then show how the AR5 projections (from 2007 onwards) compare against the observations, and find that they are highly consistent with each other. Finally, we discuss how to further improve sea-level projections in future studies.

How to cite: Slangen, A., Palmer, M., Camargo, C., Church, J., Edwards, T., Hermans, T., Hewitt, H., Garner, G., Gregory, J., Kopp, R., Malagon Santos, V., and van de Wal, R.: Sea-level projections in recent IPCC reports: how we got here, where we are and where we’re going , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9008, https://doi.org/10.5194/egusphere-egu24-9008, 2024.

Posters virtual: Thu, 18 Apr, 14:00–15:45 | vHall X5

Display time: Thu, 18 Apr, 08:30–Thu, 18 Apr, 18:00
vX5.31
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EGU24-1322
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British archaeology verifies 5th-Century rapid multi-metre sea-level rise and portends another before 2100 
Roger Higgs

Worldwide geological markers of former sea-level (SL), such as wave-cut benches (raised, drowned), reveal a ~3-metre(m) SL rise, loosely carbon-dated post-50AD/pre-600. This "Rottnest Transgression" is the youngest of several m-scale rises, interspersed with m-scale falls, on Fairbridge's (1961) global-compilation Holocene-interglacial SL curve.

Copious British archaeological evidence (email me for sources), far better-dated (pottery-sherds/dendrochronology/Roman coins), confirms the Rottnest ("Romano-British marine transgression" of Godwin 1955), verifies its amplitude (~3m), and shows it spanned only ~70 years(y), ~430-500AD (early Dark Ages; Romans abandoned Britain 410AD). (An equally fast global SL rise, ~3m in decades, is proven by last-interglacial reef-facies relationships in tectonically stable Yucatan.) The Rottnest explains 5th-Century(C) mass-migration, underway by 450AD (dendro/artefacts/skeletal-DNA), of Saxon- and Angle civilians to SE Britain ('pre-subjugated' by rebellious Saxon mercenaries by 441AD), their North-Sea-coastal-plain homelands intolerably 'squeezed' between west-advancing Huns and rapid eastward shore-retreat. Among other British evidence: (1) Pevensey sea-fort (Roman-built ~290AD) straddles a promontory pointing NE into Pevensey Levels (reclaimed former tidal-flat embayment, beside English Channel). Indicating that high-spring-tide-level (HSTL) rose >2m in the 5thC, a defensive-ditch fronting the fort's SW gate contains "tidal" mud, dated early-5thC (sherds), whose top is ~1m higher than the NW-wall foundation and <0.5m higher than the SE foundation. This explains wall-collapse in both sectors (outward-toppled slabs visible on GoogleEarth), undermined by waves/currents, no later than mid-or-late 5thC (age of Early-Saxon-style sherd in sediment draping excavated wall-stump). Subsequent HSTL fall enabled William the Conqueror's 1066AD disembarkation at Pevensey fort; (2) excavated remnant stumps of Londinium's Thames-estuary-side city-wall (~270-300AD), up to 2.5m tall, show their entire outer face eroded (wall thinned ~50%), implying HSTL rose 3+m post-construction. Confirming this rise and its likely 5thC timing, across the Thames (Southwark) a peat layer containing 4thC sherds is capped by 2.8m of barren "river clay", reaching 3.2m higher than Londinium's lowest-known Thames-side wall-foundation. Proving HSTL soon fell 2+m, 1km upstream, in Lundenwic (Saxon port founded late-5thC), a building-floor dated ~700-750AD (sherds) is 1.6m lower than Londinium's highest-known wall erosion, and 1.5m below the top of the river-clay.

Such a large/fast global SL rise implies a peri-Antarctic 'MICI' ice-cliff-collapse event (Greenland lacks requisite >1km-deep grounding-line). Regarding causation, the Rottnest rise began (~430AD) only ~25y after the ~405AD warmest Arctic temperature-spike of the period 1-2000AD. This spike followed ~100y after the Sun's 310AD strongest magnetic-grand-maximum (MGM) peak of the interval 1-1885AD. The ~100y lag is attributable to ocean-thermal-inertia. The additional ~25y lag in SL response (Rottnest start) may reflect AMOC 'conveyor-belt' oceanic-circulation, specifically the time needed for ocean-surface-water, 'overwarmed' by the MGM (Svensmark effect, reduced cloudiness), to down-well in the north-Atlantic (Arctic fringe), then travel south, then up-well and encircle Antarctica, unleashing ice-collapse. The resulting iceberg-armada would cool the ocean, hence the atmosphere, causing increased global snowfall (ice build-up), intrinsically lowering SL.

Due to anthropogenic warming, the Arctic's average-surface-air-temperature exceeds, since 2005, the 405AD peak. This portends another rapid, metre-scale SL rise, beginning ~2030 (25y lag, above). Before 2100 the time-lagged effect of the Sun's even-stronger 1991 MGM peak will exacerbate warming.

How to cite: Higgs, R.: British archaeology verifies 5th-Century rapid multi-metre sea-level rise and portends another before 2100, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1322, https://doi.org/10.5194/egusphere-egu24-1322, 2024.