Steric Sea Level Changes from Ocean Reanalyses at Global and Regional Scales

Andrea Storto,Antonio Bonaduce,Xiangbo Feng,Chunxue Yang

doi:10.3390/w11101987

Abstract

Sea level has risen significantly in the recent decades and is expected to rise further based on recent climate projections. Ocean reanalyses that synthetize information from observing networks, dynamical ocean general circulation models, and atmospheric forcing data offer an attractive way to evaluate sea level trend and variability and partition the causes of such sea level changes at both global and regional scales. Here, we review recent utilization of reanalyses for steric sea level trend investigations. State-of-the-science ocean reanalysis products are then used to further infer steric sea level changes. In particular, we used an ensemble of centennial reanalyses at moderate spatial resolution (between 0.5 × 0.5 and 1 × 1 degree) and an ensemble of eddy-permitting reanalyses to quantify the trends and their uncertainty over the last century and the last two decades, respectively. All the datasets showed good performance in reproducing sea level changes. Centennial reanalyses reveal a 1900–2010 trend of steric sea level equal to 0.47 ± 0.04 mm year−1, in agreement with previous studies, with unprecedented rise since the mid-1990s. During the altimetry era, the latest vintage of reanalyses is shown to outperform the previous ones in terms of skill scores against the independent satellite data. They consistently reproduce global and regional upper ocean steric expansion and the association with climate variability, such as ENSO. However, the mass contribution to the global mean sea level rise is varying with products and its representability needs to be improved, as well as the contribution of deep and abyssal waters to the steric sea level rise. Similarly, high-resolution regional reanalyses for the European seas provide valuable information on sea level trends, their patterns, and their causes.

Highlights

Sea level rise in the European north-western shelf area is attenuated compared to the regional reanalyses, and the Mediterranean Sea sea level fall, due again to the halosteric sea level, is mitigated
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Theshow results that reanalyses are a powerful tool for steric sea level investigations, as they provide performances ocean reanalyses are a powerful tool for steric sea level investigations, as they provide performances comparable moretraditional traditionalmethods methods (e.g., and allow comparable totomore objectiveanalyses, analyses,sea sealevel level reconstructions) and allow for process-oriented studies because of their consistent multi-variate ocean state reconstruction

Summary

Introduction

Sea Level Rise as a Proxy of Climate Change and Threat from Global Warming. Sea level rise has been long used as an indicator to monitor the Earth’s energy imbalance and the associated global warming [1,2], and simultaneously represents one of the most prominent threats that climate change poses to the large human population inhabiting coastal [3]. Sea level rise is mostly related to the expansion of water masses due to density variations (steric effect) and to the increase of water masses due to ice-sheet and glacier melting, and redistribution of the water cycle between different Earth system components. At long time scales (e.g., multi-decadal to centennial), other non-negligible factors exist for sea level changes, such as perturbations in the Earth’s rotation [7] and the effect of geothermal fluxes [8]

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