scholarly journals A Surrogate Ensemble Study of Sea Level Reconstructions

2010 ◽  
Vol 23 (16) ◽  
pp. 4306-4326 ◽  
Author(s):  
Bo Christiansen ◽  
T. Schmith ◽  
P. Thejll
Keyword(s):  
Sea Level ◽  
Covariance Structure ◽  
Optimal Interpolation ◽  
Tide Gauges ◽  
Sea Levels ◽  
Calibration Period ◽  
Interpolation Methods ◽  
Reconstruction Methods ◽  
Homogeneous Pattern ◽  
Global Mean

Abstract This study investigates the possibility of reconstructing past global mean sea levels. Reconstruction methods rely on historical measurements from tide gauges combined with knowledge about the spatial covariance structure of the sea level field obtained from a shorter period with spatially well-resolved satellite measurements. A surrogate ensemble method is applied based on sea levels from a 500-yr climate model simulation. Tide gauges are simulated by selecting time series from grid points along continental coastlines and on ocean islands. Reconstructions of global mean sea levels can then be compared to the known target, and the ensemble method allows an estimation of the statistical properties originating from the stochastic nature of the reconstructions. Different reconstruction methods previously used in the literature are studied, including projection and optimal interpolation methods based on EOF analysis of the calibration period. This study also includes methods where these EOFs are augmented with a homogeneous pattern, with the purpose of better capturing a possible geographically homogeneous trend. These covariance-based methods are compared to a simple weighted mean method. It is concluded that the projection and optimal interpolation methods are very sensitive to the length of the calibration period. For realistic lengths of 10 and 20 yr, very large biases and spread in the reconstructed 1900–49 trends are found. Including a homogeneous pattern in the basis drastically improves the reconstructions of the trend and reduces the sensitivity to the length of the calibration period. The projection and optimal interpolation methods are now comparable to the weighted mean with biases less than 10% in the trend. However, the spread is still considerable. The amplitude of the year-to-year variability is in general strongly overestimated by all reconstruction methods. With regards to year-to-year variability, several methods outperform the simple mean. Finally, for the projection method, reconstruction errors are decomposed into contributions from the sparse coverage of tide gauges and the incomplete knowledge of the covariance structure of the sea level field. The study finds that the contributions of the different sources depend on the diagnostics of the reconstruction. It is noted that sea level is constrained by the approximate conservation of the total mass of the ocean. This poses challenges for the sea level reconstructions that are not present for other fields such as temperature.

The actual measurements at the tide gauges do not support strongly accelerating twentieth-century sea-level rise reconstructions

2016 ◽  
Vol 5 (1) ◽  
Author(s):  
A. Parker
Keyword(s):  
Twentieth Century ◽  
Sea Level Rise ◽  
Sea Level ◽  
Tide Gauges ◽  
Mean Sea Level ◽  
Sea Levels ◽  
Global Mean Sea Level ◽  
Global Mean

AbstractContrary to what is claimed by reconstructions of the Global Mean Sea Level (GMSL) indicating accelerating sea level rates of rise over the twentieth-century, the actual measurements at the tide gauges show the sea levels have not risen nor accelerated that much. The most recent estimation by Hay et al [

scholarly journals Twenty-first century response of Petermann Glacier, northwest Greenland to ice shelf loss

2020 ◽  
pp. 1-11
Author(s):  
Emily A. Hill ◽  
G. Hilmar Gudmundsson ◽  
J. Rachel Carr ◽  
Chris R. Stokes ◽  
Helen M. King
Keyword(s):  
Sea Level ◽  
First Century ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Sea Levels ◽  
Grounding Line ◽  
Global Mean Sea Level ◽  
Near Future ◽  
Global Mean ◽  
Large Sections

Abstract Ice shelves restrain flow from the Greenland and Antarctic ice sheets. Climate-ocean warming could force thinning or collapse of floating ice shelves and subsequently accelerate flow, increase ice discharge and raise global mean sea levels. Petermann Glacier (PG), northwest Greenland, recently lost large sections of its ice shelf, but its response to total ice shelf loss in the future remains uncertain. Here, we use the ice flow model Úa to assess the sensitivity of PG to changes in ice shelf extent, and to estimate the resultant loss of grounded ice and contribution to sea level rise. Our results have shown that under several scenarios of ice shelf thinning and retreat, removal of the shelf will not contribute substantially to global mean sea level (<1 mm). We hypothesize that grounded ice loss was limited by the stabilization of the grounding line at a topographic high ~12 km inland of its current grounding line position. Further inland, the likelihood of a narrow fjord that slopes seawards suggests that PG is likely to remain insensitive to terminus changes in the near future.

scholarly journals Influence of MeteOcean processes on MSYM sea level predictions in the Malacca Straits

2018 ◽  
Vol 2 (2) ◽  
Author(s):  
Sofia Bartolomeu ◽  
Madalena S. Malhadas ◽  
João Ribeiro ◽  
Paulo C. Leitão ◽  
João M. Dias
Keyword(s):  
Sea Level ◽  
Oil Spill ◽  
Surface Wind ◽  
Model Performance ◽  
Tide Gauges ◽  
Tidal Dynamics ◽  
Dynamic Complexity ◽  
Sea Levels ◽  
Astronomical Tide ◽  
Malacca Strait

The South China Sea region, and particularly the Malacca and Singapore Straits, are known by the complex tidal dynamics, which is influenced by the tidal propagation from Pacific and Indian Oceans. In spite of the dynamic complexity, the region is very relevant economically, especially concerning the growing oil drilling activities. To give support to accidental oil spill prevention and response, an operational oil spill forecast system was developed for the Strait of Malacca. The hydrodynamic system validation revealed good results, in general. However, besides all the modeling efforts, some discrepancies between observed and predicted sea levels were identified, mainly during neap tide and for specific tide-gauges. Therefore, the main aim of this study consists in researching the origin of these discrepancies by comparing predictions with available data and exploring their relation with the MeteOcean processes of the region. Initially sea level data for eight tide gauges was explored to get a general overview of the local tidal dynamics, and then the model performance for astronomic tide was assessed. Analysis of meteorological tides was also performed for three tide-gauges located in the Singapore and Malacca Strait, which are under the influence of the northeast or southwest monsoons. The results show that the differences between the observed and predicted sea levels in Singapore Strait are usually due to discrepancies in the meteorological tide induced by the surface wind stress acting over the Taiwan-Singapore axis, while in the Malacca Strait are mainly related with model limitations in reproducing the astronomical tide.

scholarly journals Pacific Sea Levels Rising Very Slowly and Not Accelerating

2019 ◽  
Vol 38 (1) ◽  
pp. 179-184 ◽  
Author(s):  
Albert Parker ◽  
Clifford Ollier
Keyword(s):  
Pacific Ocean ◽  
Sea Level ◽  
Relative Rate ◽  
Tide Gauges ◽  
Sea Levels ◽  
The Past ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Long Term Trend

AbstractOver the past decades, detailed surveys of the Pacific Ocean atoll islands show no sign of drowning because of accelerated sea-level rise. Data reveal that no atoll lost land area, 88.6% of islands were either stable or increased in area, and only 11.4% of islands contracted. The Pacific Atolls are not being inundated because the sea level is rising much less than was thought. The average relative rate of rise and acceleration of the 29 long-term-trend (LTT) tide gauges of Japan, Oceania and West Coast of North America, are both negative, −0.02139 mm yr−1and −0.00007 mm yr−2respectively. Since the start of the 1900s, the sea levels of the Pacific Ocean have been remarkably stable.

The transient sensitivity of sea level rise

2020 ◽  
Author(s):  
Aslak Grinsted ◽  
Jens Hesselbjerg Christensen
Keyword(s):  
Surface Temperature ◽  
Sea Level Rise ◽  
Sea Level ◽  
Rate Of Change ◽  
Expert Elicitation ◽  
Coastal Communities ◽  
Observational Period ◽  
Sea Levels ◽  
Global Mean Surface Temperature ◽  
Global Mean

&lt;p&gt;We are warming our planet, and sea levels are rising as oceans expand and ice on land melts. This instigates a threat to coastal communities and ecosystems, and there is an urgent need for sea level predictions encompassing all known uncertainties to plan for it. Comprehensive assessments have concluded that sea level is unlikely to rise by more than about 1.1m this century but with further increase beyond 2100. However, some studies conclude that considerably greater sea level rise could be realised and an expert elicitation assign a substantially higher likelihood to this scenario. Here, we show that models used to assess future sea level in AR5 &amp; SROCC have a lower sea level sensitivity than inferred from observations. By analyzing mean rate of change in sea level (not sea level itself), we identify a near linear relationship with global mean surface temperature in both model projections, and in observations. The model projections fall below expectations from the more recent observational period. This comparison suggests that the likely range of sea level projections in IPCC AR5 and SROCC would be too low.&lt;/p&gt;

scholarly journals Long-Term, Seasonal and Short-Term Fluctuations in the Water Level of the Southern Baltic Sea

2014 ◽  
Vol 33 (3) ◽  
pp. 181-197 ◽  
Author(s):  
Tomasz Wolski ◽  
Bernard Wiśniewski
Keyword(s):  
Baltic Sea ◽  
Water Level ◽  
Sea Level ◽  
Tide Gauges ◽  
Short Term ◽  
Sea Levels ◽  
Extreme Sea Levels ◽  
Solar Tide ◽  
Southern Baltic

Abstract Aim of this work are analyses of oscillations sea levels in the Southern Baltic on a scale of short-term changes, seasonal and long-term (age). The study was based on observational data in different periods time for tide gauges station of the Polish coast. On the example of some storm situations presents the part of the baric wave and the wind in the formation of extreme sea levels. The primary cause of the annual variability of sea levels was the characteristics of the annual and semi-annual oscillations (the annual and semi-annual solar tide). In the work also determined the rate of long-term sea-level rise for the Polish coast.

scholarly journals Measuring Global-Mean Sea-Level Rise With Surface Drifting Buoys

2021 ◽  
Vol 55 (3) ◽  
pp. 66-67
Author(s):  
Shane Elipot ◽  
Luca Centurioni ◽  
Bruce J. Haines ◽  
Rick Lumpkin ◽  
Josh K. Willis
Keyword(s):  
Sea Level ◽  
Tide Gauge ◽  
Satellite System ◽  
Global Ocean ◽  
Vertical Position ◽  
Sea Level Changes ◽  
Mean Sea Level ◽  
Sea Levels ◽  
Global Mean ◽  
Drifting Buoys

Abstract We propose to establish a new ocean observing system for monitoring global and regional mean sea-level changes. This system will consist of a global array of thousands of water-following drifting buoys tracked by a global navigation satellite system—such as the Global Positioning System (GPS)—which will continuously provide the geographical positions and the height of the sea surface along the buoys' trajectories. The sea-level height data collected in this way, averaged over regional basins and the global ocean, will provide daily measures of regional and global mean sea levels. An essential climate variable, mean sea level is an intrinsic measure of climate change, integrating the thermal expansion of the ocean's waters and additions to the ocean's mass from melting terrestrial ice. The realization of this new system requires that standardized vertical position measurements with controlled accuracy be acquired and regularly transmitted from relatively small and expendable drifting buoys, which constitutes a technological challenge, yet one with a clear path for being met. The development and implementation of this ocean shot concept will ultimately provide an independent, resilient, sustainable, and economical observational system to quantify natural and anthropogenic sea-level changes, augmenting the existing satellites and tide gauge observing systems.

scholarly journals Analysis on the Extreme Sea Levels Changes along the Coastline of Bohai Sea, China

Atmosphere ◽  
2018 ◽  
Vol 9 (8) ◽  
pp. 324 ◽  
Author(s):  
Jianlong Feng ◽  
Delei Li ◽  
Hui Wang ◽  
Qiulin Liu ◽  
Jianli Zhang ◽  
...  
Keyword(s):  
Sea Level ◽  
Bohai Sea ◽  
High Tide ◽  
Tide Gauges ◽  
Mean Sea Level ◽  
Sea Levels ◽  
The Bohai Sea ◽  
Extreme Sea Levels ◽  
The Mean

Using hourly sea level data from four tide gauges, the changes of the extreme sea level in the Bohai Sea were analyzed in this work. Three components (i.e., mean sea level, tide and surge) as well as the tide–surge interaction were studied to find which component was important in the changes of extreme sea levels. Significant increasing trends exist in the mean sea level at four tide gauges from 1980 to 2016, and the increase rate ranges from 0.2 to 0.5 cm/year. The mean high tide levels show positive trends at four tide gauges, and the increasing rate (0.1 to 0.3 cm/year) is not small compared with the long-term trends of the mean sea levels. However, the mean tidal ranges show negative trends at Longkou, Qinhuangdao and Tanggu, with the rate from about −0.7 to −0.2 cm/year. At Qinhuangdao and Tanggu, the annual surge intensity shows explicit long-term decreasing trend. At all four tide gauges, the storm surge intensity shows distinct inter-annual variability and decadal variability. All four tide gauges show significant tide–surge interaction, the characteristics of the tide–surge interaction differ due to their locations, and no clear long-term change was found. Convincing evidence implies that the extreme sea levels increase during the past decades from 1980 to 2016 at all tide gauges, with the increasing rate differing at different percentile levels. The extreme sea level changes in the Bohai Sea are highly affected by the changes of mean sea level and high tide level, especially the latter. The surge variation contributes to the changes of extreme sea level at locations where the tide–surge interaction is relatively weak.

scholarly journals Nonlinear absolute sea-level patterns in the long-term-trend tide gauges of the East Coast of North America

2021 ◽  
Vol 10 (1) ◽  
pp. 1-15
Author(s):  
Alberto Boretti
Keyword(s):  
North America ◽  
Sea Level ◽  
East Coast ◽  
Tide Gauge ◽  
Tide Gauges ◽  
Sea Levels ◽  
Term Trend ◽  
The Absolute ◽  
Long Term Trend

Abstract The paper provides an estimate of the latest relative and absolute rates of rise and accelerations of the sea levels for the East Coast of North America. The computation is based on the long-term trend (LTT) tide gauge records of the relative sea levels and the Global Navigation Satellite System (GNSS) time series of the absolute position of fixed dome nearby the tide gauges. The GNSS result is used to infer the subsidence or uplift of the tide gauge instrument. The data of 33 LTT tide stations with more than 80 years of data are shown. The average relative sea-level rise is +2.22 mm/yr. subjected to a small, positive average acceleration of +0.0027 mm/yr2. The average absolute velocity of the tide gauge instruments is −0.52 mm/yr. translating in an average absolute sea-level rise of +1.70 mm/yr. This is the first paper publishing a comprehensive survey of the absolute sea-level rates of rise along the East Coast of North America using the reliable information of relative sea-level rates of rise from LTT tide gauges, plus the absolute subsidence rates from GNSS antennas that are close to the tide gauges installations.

Venice: Rising Water or Sinking Land?

2015 ◽  
Vol 4 (3) ◽  
Author(s):  
A. Parker ◽  
C.D. Ollier
Keyword(s):  
Carbon Dioxide ◽  
Thermal Expansion ◽  
Global Warming ◽  
Sea Level Rise ◽  
Sea Level ◽  
Carbon Dioxide Production ◽  
Tide Gauges ◽  
Relative Sea Level ◽  
Sea Levels ◽  
Anthropogenic Carbon

AbstractThe recent paper by Bellfiore, Ghezzo, Tagliapietra and Umgiesser [1] gives us the opportunity to discuss the relative sea level rise in Venice (Venezia). They accept that the Venetian sea level rise will be part of a global rise caused by ocean thermal expansion and melting of icecaps caused in turn by global warming induced by anthropogenic carbon dioxide production. In reality the sea levels have been only oscillating during the last few decades. Theworldwide average sea level rise is free of any acceleration. This is also true for theVenice and Trieste tide gauges. The sea level records of Venice and Trieste are very different, and it is impossible for two places so close together to have such differences from a common rise in sea level. Venice is sinking relative to Trieste.

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