Multitechnique Assessment of the Interannual to Multidecadal Variability in Steric Sea Levels: A Comparative Analysis of Climate Mode Fingerprints

Because of increased emissions of greenhouse gases oceans are warming, causing sea level to rise as the density of seawater falls. Predicting the rates of steric expansion is challenging because of the natural variability of the ocean and because observations are insufficient to adequately cover the ocean basins. Here, we investigate the ability of one ocean reanalysis, two objective analyses, and one combination of satellite geodetic measurements to accommodate data gaps and to reconstruct typical patterns of the steric sea level variability at interannual and multidecadal time scales. Six climate indices are used to identify robust features of the internal variability, using a Least Absolute Shrinkage and Selection Operator (LASSO) regression to select significant predictors of the steric variability. Spatially consistent fingerprints are revealed for all climate indices in the ocean reanalysis dataset, allowing the recovery of most of the steric variability observed in the tropical and North Pacific, as well as large fractions of the Atlantic and Indian Ocean signals. Robust climate mode fingerprints are also identified with high spatial resolution but limited temporal coverage in the geodetic observations. The objective analyses fail to detect many of the patterns expected from climate modes, especially before the Argo era. Climate indices constitute valuable yet underexploited tools to assess the performance of different techniques to reconstruct steric sea levels at interannual and multidecadal scales. Such progress will increase confidence in the historical reconstructions of steric sea levels, which is necessary to improve the closure of regional and global sea level budgets and to validate the predictions of climate models.

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Climate Drift in the CMIP5 Models*

Journal of Climate ◽

10.1175/jcli-d-12-00521.1 ◽

2013 ◽

Vol 26 (21) ◽

pp. 8597-8615 ◽

Cited By ~ 128

Author(s):

Alexander Sen Gupta ◽

Nicolas C. Jourdain ◽

Jaclyn N. Brown ◽

Didier Monselesan

Keyword(s):

Climate Models ◽

Coupled Model ◽

Deep Ocean ◽

Internal Variability ◽

Correction Method ◽

Physical Models ◽

Cmip5 Models ◽

Steric Sea Level ◽

Biogeochemical Models ◽

The Difference

Abstract Climate models often exhibit spurious long-term changes independent of either internal variability or changes to external forcing. Such changes, referred to as model “drift,” may distort the estimate of forced change in transient climate simulations. The importance of drift is examined in comparison to historical trends over recent decades in the Coupled Model Intercomparison Project (CMIP). Comparison based on a selection of metrics suggests a significant overall reduction in the magnitude of drift from phase 3 of CMIP (CMIP3) to phase 5 of CMIP (CMIP5). The direction of both ocean and atmospheric drift is systematically biased in some models introducing statistically significant drift in globally averaged metrics. Nevertheless, for most models globally averaged drift remains weak compared to the associated forced trends and is often smaller than the difference between trends derived from different ensemble members or the error introduced by the aliasing of natural variability. An exception to this is metrics that include the deep ocean (e.g., steric sea level) where drift can dominate in forced simulations. In such circumstances drift must be corrected for using information from concurrent control experiments. Many CMIP5 models now include ocean biogeochemistry. Like physical models, biogeochemical models generally undergo long spinup integrations to minimize drift. Nevertheless, based on a limited subset of models, it is found that drift is an important consideration and must be accounted for. For properties or regions where drift is important, the drift correction method must be carefully considered. The use of a drift estimate based on the full control time series is recommended to minimize the contamination of the drift estimate by internal variability.

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Tropical Pacific spatial trend patterns in observed sea level: internal variability and/or anthropogenic signature?

Climate of the Past ◽

10.5194/cp-8-787-2012 ◽

2012 ◽

Vol 8 (2) ◽

pp. 787-802 ◽

Cited By ~ 67

Author(s):

B. Meyssignac ◽

D. Salas y Melia ◽

M. Becker ◽

W. Llovel ◽

A. Cazenave

Keyword(s):

Sea Level ◽

Climate Models ◽

Internal Variability ◽

Tropical Pacific ◽

External Forcing ◽

Spatial Trend ◽

Trend Pattern ◽

Coupled Climate Models ◽

Sea Level Trend ◽

The Tropical Pacific

Abstract. In this study we focus on the sea level trend pattern observed by satellite altimetry in the tropical Pacific over the 1993–2009 time span (i.e. 17 yr). Our objective is to investigate whether this 17-yr-long trend pattern was different before the altimetry era, what was its spatio-temporal variability and what have been its main drivers. We try to discriminate the respective roles of the internal variability of the climate system and of external forcing factors, in particular anthropogenic emissions (greenhouse gases and aerosols). On the basis of a 2-D past sea level reconstruction over 1950–2009 (based on a combination of observations and ocean modelling) and multi-century control runs (i.e. with constant, preindustrial external forcing) from eight coupled climate models, we have investigated how the observed 17-yr sea level trend pattern evolved during the last decades and centuries, and try to estimate the characteristic time scales of its variability. For that purpose, we have computed sea level trend patterns over successive 17-yr windows (i.e. the length of the altimetry record), both for the 60-yr long reconstructed sea level and the model runs. We find that the 2-D sea level reconstruction shows spatial trend patterns similar to the one observed during the altimetry era. The pattern appears to have fluctuated with time with a characteristic time scale of the order of 25–30 yr. The same behaviour is found in multi-centennial control runs of the coupled climate models. A similar analysis is performed with 20th century coupled climate model runs with complete external forcing (i.e. solar plus volcanic variability and changes in anthropogenic forcing). Results suggest that in the tropical Pacific, sea level trend fluctuations are dominated by the internal variability of the ocean–atmosphere coupled system. While our analysis cannot rule out any influence of anthropogenic forcing, it concludes that the latter effect in that particular region is stillhardly detectable.

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Atmospheric circulation changes and their impact on extreme sea levels around Australia

Natural Hazards and Earth System Science ◽

10.5194/nhess-19-1067-2019 ◽

2019 ◽

Vol 19 (5) ◽

pp. 1067-1086 ◽

Cited By ~ 4

Author(s):

Frank Colberg ◽

Kathleen L. McInnes ◽

Julian O'Grady ◽

Ron Hoeke

Keyword(s):

Sea Level ◽

Large Scale ◽

Climate Models ◽

Tide Gauge ◽

Austral Summer ◽

Sea Level Changes ◽

Sea Level Variability ◽

Sea Levels ◽

Extreme Sea Levels ◽

Coastal Sea

Abstract. Projections of sea level rise (SLR) will lead to increasing coastal impacts during extreme sea level events globally; however, there is significant uncertainty around short-term coastal sea level variability and the attendant frequency and severity of extreme sea level events. In this study, we investigate drivers of coastal sea level variability (including extremes) around Australia by means of historical conditions as well as future changes under a high greenhouse gas emissions scenario (RCP 8.5). To do this, a multi-decade hindcast simulation is validated against tide gauge data. The role of tide–surge interaction is assessed and found to have negligible effects on storm surge characteristic heights over most of the coastline. For future projections, 20-year-long simulations are carried out over the time periods 1981–1999 and 2081–2099 using atmospheric forcing from four CMIP5 climate models. Changes in extreme sea levels are apparent, but there are large inter-model differences. On the southern mainland coast all models simulated a southward movement of the subtropical ridge which led to a small reduction in sea level extremes in the hydrodynamic simulations. Sea level changes over the Gulf of Carpentaria in the north are largest and positive during austral summer in two out of the four models. In these models, changes to the northwest monsoon appear to be the cause of the sea level response. These simulations highlight a sensitivity of this semi-enclosed gulf to changes in large-scale dynamics in this region and indicate that further assessment of the potential changes to the northwest monsoon in a larger multi-model ensemble should be investigated, together with the northwest monsoon's effect on extreme sea levels.

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Modelling the Antarctic Ice Sheet in the warm Mid-Pliocene

10.5194/egusphere-egu2020-19348 ◽

2020 ◽

Author(s):

James O'Neill ◽

Tamsin Edwards ◽

Lauren Gregoire ◽

Niall Gandy ◽

Aisling Dolan ◽

...

Keyword(s):

Sea Level ◽

Climate Models ◽

Phase 1 ◽

Ice Sheet ◽

Latin Hypercube Design ◽

Antarctic Ice Sheet ◽

Sea Levels ◽

Ocean Climate ◽

Parameter Values ◽

The Antarctic

The Antarctic ice sheet is a deeply uncertain component of future sea level under anthropogenic climate change. To shed light on the ice sheets response to warmer climates in the past and its&#8217; response to future warming, periods in Earth&#8217;s geological record can serve as instructive modelling targets. The mid-Pliocene warm period (3.3 &#8211; 3.0 Ma) is characterised by global mean surface temperatures ~2.7-4oC above pre-industrial, atmospheric CO2&#160;concentrations of ~400ppm&#160;and eustatic sea level rise on the order of ~10-30m above modern. The mid-Pliocene sea level record is subject to large uncertainties. The upper end of this record implies a significant contribution from Antarctica and possible collapse of regions of the ice sheet, driven by marine ice sheet instabilities.We present a suite of BISICLES ice sheet model&#160;simulations, forced with a subset of Pliocene Modelling Intercomparison Project (PlioMIP phase 1) coupled atmosphere-ocean climate models, that represent the Pliocene Antarctic ice sheet. This ensemble captures a range of possible ice sheet model responses to a warm Pliocene-like climate under different parameter choices, sampled in a Latin hypercube design. Modelled Antarctic sea level contribution is compared to reconstructions of Pliocene sea level, to explore the extent to which available data with large uncertainties can constrain the model parameter values.Our aim with this work is to provide insights on Antarctic contribution to sea level in the warm mid-Pliocene. We seek to characterise the role of ice-ocean, ice-atmosphere and ice-bedrock parameter uncertainty in BISICLES on the ice sheet sea level contribution range, and whether cliff instability processes are necessary in reproduce high Pliocene sea levels in this ice sheet model.

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Atmospheric Circulation Changes and their Impact on Extreme Sea Levels around Australia

10.5194/nhess-2018-64 ◽

2018 ◽

Author(s):

Frank Colberg ◽

Kathleen L. McInnes ◽

Julian O'Grady ◽

Ron K. Hoeke

Keyword(s):

Sea Level ◽

Atmospheric Circulation ◽

Climate Models ◽

Tide Gauge ◽

Austral Summer ◽

Sea Level Variability ◽

Sea Levels ◽

Extreme Sea Levels ◽

Coastal Sea ◽

Circulation Changes

Abstract. Projections of sea level rise (SLR) will lead to increasing coastal impacts during extreme sea level events globally, however, there is significant uncertainty around short-term coastal sea level variability and the attendant frequency and severity of extreme sea level events. In this study, we investigate drivers of coastal sea level variability (including extremes) around Australia by means of historical conditions as well as future changes under a high greenhouse gas emissions scenario (RCP8.5). To do this, a multi-decade hindcast simulation is validated against tide gauge data. The role of tide-surge interaction is assessed and found to have negligible effects on storm surge characteristic heights over most of the coastline. For future projections, twenty-year long simulations are carried out over the time periods 1981–1999 and 2081–2099 using atmospheric forcing from four CMIP5 climate models. Results provide insights into how future atmospheric circulation changes may impact Australia's coastal zone and highlight regions of potential sensitivity to atmospheric circulation changes. Areas of note are the Gulf of Carpentaria in the north where changes to the northwest monsoon could lead to relatively large increases in extreme sea levels during Austral summer. For the southern mainland coast the simulated scenarios suggest that a southward movement of the subtropical ridge leads to a small reduction in sea level extremes.

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Statistical Analysis of Global Surface Temperature and Sea Level Using Cointegration Methods

Journal of Climate ◽

10.1175/jcli-d-11-00598.1 ◽

2012 ◽

Vol 25 (22) ◽

pp. 7822-7833 ◽

Cited By ~ 31

Author(s):

Torben Schmith ◽

Søren Johansen ◽

Peter Thejll

Keyword(s):

Surface Temperature ◽

Sea Level ◽

Radiative Forcing ◽

Climate Models ◽

Cointegration Analysis ◽

Sea Levels ◽

Ice Caps ◽

Physically Based ◽

Ice Sheet Dynamics ◽

Global Sea Level

Abstract Global sea level rise is widely understood as a consequence of thermal expansion and the melting of glaciers and land-based ice caps. Because of the lack of representation of ice-sheet dynamics in present-day physically based climate models, semiempirical models have been applied as an alternative for projecting future sea levels. There are, however, potential pitfalls in this because of the trending nature of the time series. A statistical method called cointegration analysis that is capable of handling such peculiarities is applied to observed global sea level and land–ocean surface temperature. The authors find a relationship between sea level and temperature and find that temperature causally depends on the sea level, which can be understood as a consequence of the large heat capacity of the ocean. They further find that the warming episode in the 1940s is exceptional in the sense that sea level and warming deviate from the expected relationship. This suggests that this warming episode is mainly due to internal dynamics of the ocean rather than external radiative forcing. On the other hand, the present warming follows the expected relationship, suggesting that it is mainly due to radiative forcing. In a second step, the total radiative forcing is used as an explanatory variable, but it is unexpectedly found that the sea level does not depend on the forcing. The authors hypothesize that this is due to a long adjustment time scale of the ocean and show that the number of years of data needed to build statistical models that have the relationship expected from physics exceeds what is currently available by a factor of almost 10.

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The long-term variability of extreme sea levels in the German Bight

Ocean Science ◽

10.5194/os-15-651-2019 ◽

2019 ◽

Vol 15 (3) ◽

pp. 651-668 ◽

Cited By ~ 4

Author(s):

Andreas Lang ◽

Uwe Mikolajewicz

Keyword(s):

Sea Level ◽

German Bight ◽

Large Scale ◽

Internal Variability ◽

Climate System ◽

System Model ◽

Tide Gauge Record ◽

Sea Levels ◽

The North

Abstract. Extreme high sea levels (ESLs) caused by storm floods constitute a major hazard for coastal regions. We here quantify their long-term variability in the southern German Bight using simulations covering the last 1000 years. To this end, global earth system model simulations from the PMIP3 past1000 project are dynamically scaled down with a regionally coupled climate system model focusing on the North Sea. This approach provides an unprecedented long high-resolution data record that can extend the knowledge of ESL variability based on observations, and allows for the identification of associated large-scale forcing mechanisms in the climate system. While the statistics of simulated ESLs compare well with observations from the tide gauge record at Cuxhaven, we find that simulated ESLs show large variations on interannual to centennial timescales without preferred oscillation periods. As a result of this high internal variability, ESL variations appear to a large extent decoupled from those of the background sea level, and mask any potential signals from solar or volcanic forcing. Comparison with large-scale climate variability shows that periods of high ESL are associated with a sea level pressure dipole between northeastern Scandinavia and the Gulf of Biscay. While this large-scale circulation regime applies to enhanced ESL in the wider region, it differs from the North Atlantic Oscillation pattern that has often been linked to periods of elevated background sea level. The high internal variability with large multidecadal to centennial variations emphasizes the inherent uncertainties related to traditional extreme value estimates based on short data subsets, which fail to account for such long-term variations. We conclude that ESL variations as well as existing estimates of future changes are likely to be dominated by internal variability rather than climate change signals. Thus, larger ensemble simulations will be required to assess future flood risks.

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Indo-Pacific Climate Modes in Warming Climate: Consensus and Uncertainty Across Model Projections

Current Climate Change Reports ◽

10.1007/s40641-019-00152-9 ◽

2019 ◽

Vol 5 (4) ◽

pp. 308-321 ◽

Cited By ~ 3

Author(s):

Xiao-Tong Zheng

Keyword(s):

Climate Models ◽

Internal Variability ◽

Forced Response ◽

Future Climate Change ◽

Climate Modes ◽

Warming Climate ◽

Warming Pattern ◽

Large Ensembles ◽

Projected Changes ◽

Climate Mode

Abstract Purpose of Review Understanding the changes in climate variability in a warming climate is crucial for reliable projections of future climate change. This article reviews the recent progress in studies of how climate modes in the Indo-Pacific respond to greenhouse warming, including the consensus and uncertainty across climate models. Recent Findings Recent studies revealed a range of robust changes in the properties of climate modes, often associated with the mean state changes in the tropical Indo-Pacific. In particular, the intermodel diversity in the ocean warming pattern is a prominent source of uncertainty in mode changes. The internal variability also plays an important role in projected changes in climate modes. Summary Model biases and intermodel variability remain major challenges for reducing uncertainty in projecting climate mode changes in warming climate. Improved models and research linking simulated present-day climate and future changes are essential for reliable projections of climate mode changes. In addition, large ensembles should be used for each model to reduce the uncertainty from internal variability and isolate the forced response to global warming.

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Multidecadal internal variability role in estimating sea level acceleration: Fremantle case study

10.5194/egusphere-egu21-12075 ◽

2021 ◽

Author(s):

Armin Agha Karimi

Keyword(s):

Pacific Ocean ◽

Sea Level Rise ◽

Sea Level ◽

Low Frequency ◽

Internal Variability ◽

Anthropogenic Factors ◽

Climate Indices ◽

The Third ◽

Trajectory Models

Low frequency internal signals bring challenges to signify the role of anthropogenic factors in sea level rise and to attain a certain accuracy in trend and acceleration estimations; thus, modelling these signals is crucial. Due to both spatially and temporally poor coverage of the relevant data sets, identification of internal variability patterns is not straightforward. In this study, the identification and role of low frequency internal variability (decadal and multidecadal) in sea level change of Fremantle tide gauge station is analysed using two climate indices, Pacific Decadal Oscillation (PDO) and Tripole Interdecadal Pacific Oscillation (TPO). The wavelet transform is applied on the sea level and climate indices time series for this purpose. It is shown that the multidecadal sea level variability is anticorrelated with corresponding components of climate indices in the Pacific Ocean, with correlation coefficients of -0.9 and -0.76 for TPO and PDO, respectively. The correlations are comparatively low in decadal time scale, by correlation coefficient of approximately -0.5 for both indices. To estimate trend and acceleration in Fremantle, three trajectory models are tested. The first model is a simple second-degree polynomial comprising trend and acceleration terms. Low passed PDO, representing decadal and interdecadal variabilities in Pacific Ocean, is added to the first model to form the second model. For the third model, decomposed signals of decadal and multidecadal variability of TPO are added to the first model. For all trajectory models, different noise models are tried and according to Akaike and Bayesian information criteria, the best noise model is AR(5). In overall, TPO explains the low frequency internal variability better than PDO for sea level variation in Fremantle. Although the estimated trends does not change significantly for the three models, the estimated acceleration is substantially different. The accelerations estimated from the first and second models are statistically insignificant, 0.006 &#177; 0.012 mm.yr-2 and 0.01 &#177; 0.01 mm.yr-2 respectively, while this figure for the third model is 0.018 &#177; 0.01 mm.yr-2. The outcome exemplifies the importance of modelling low frequency internal variability in acceleration estimations for sea level rise in regional scale.

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Sea level budget over 2005–2013: missing contributions and data errors

Ocean Science Discussions ◽

10.5194/osd-12-701-2015 ◽

2015 ◽

Vol 12 (3) ◽

pp. 701-734

Author(s):

H. B. Dieng ◽

A. Cazenave ◽

K. von Schuckmann ◽

M. Ablain ◽

B. Meyssignac

Keyword(s):

Sea Level ◽

Heat Content ◽

Deep Ocean ◽

Time Span ◽

Short Time Scale ◽

Altimetry Data ◽

Ocean Reanalysis ◽

Steric Sea Level ◽

Ocean Mass ◽

The Impact

Abstract. Based on the sea level budget closure approach, this study investigates the residuals between observed global mean sea level (GMSL) and the sum of components (steric sea level and ocean mass) for the period January 2005 to December 2013. The objective is to identify the impact of errors in one or several components of the sea level budget on the residual time series. This is a key issue if we want to constrain missing contributions such as the contribution to sea level rise from the deep ocean (> 2000m). For that purpose, we use several data sets as processed by different groups: six altimetry products for the GMSL, four Argo products plus the ORAS4 ocean reanalysis for the steric sea level and three GRACE-based ocean mass products. We find that over the study time span, the observed trend differences in the residuals of the sea level budget can be as large as ~0.55mm yr−1. These trend differences essentially result from the processing of the altimetry data (e.g., choice the geophysical corrections and method of averaging the along-track altimetry data). At short time scale (from sub-seasonal to multi-annual), residual anomalies are significantly correlated with ocean mass and steric sea level anomalies (depending on the time span), indicating that the residual anomalies are related to errors in both GRACE-based ocean mass and Argo-based steric data. Efforts are needed to reduce these various sources of errors before using the sea level budget approach to estimate missing contributions such as the deep ocean heat content.

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