Exploring Sources of Uncertainty in Steric Sea‐Level Change Estimates

Abstract

Recent studies disagree about the contribution of variations in temperature and salinity of the oceans-steric change-to the observed sea-level change. This article explores two sources of uncertainty to both global mean and regional steric sea-level trends. First, we analyze the influence of different temperature and salinity data sets on the estimated steric sea-level change. Next, we investigate the impact of different stochastic noise models on the estimation of trends and their uncertainties. By varying both the data sets and noise models, the global mean steric sea-level trend and uncertainty can vary from 0.69 to 2.40 and 0.02 to 1.56 mm/year, respectively, for 1993-2017. This range is even larger on regional scales, reaching up to 30 mm/year. Our results show that a first-order autoregressive model is the most appropriate choice to describe the residual behavior of the ensemble mean of all data sets for the global mean steric sea-level change over the last 25 years, which consequently leads to the most representative uncertainty. Using the ensemble mean and the first-order autoregressive noise model, we find a global mean steric sea-level change of 1.36 ± 0.10 mm/year for 1993-2017 and 1.08 ± 0.07 mm/year for 2005-2015. Regionally, a combination of different noise models is the best descriptor of the steric sea-level change and its uncertainty. The spatial coherence in the noise model preference indicates clusters that may be best suited to investigate the regional sea-level budget. Plain Language Summary Ocean temperature and salinity variations lead to changes in sea level, known as steric sea-level change. Steric variations are important contributors to sea-level change and reflect how the oceans have been responding to global warming. For this reason, several recent studies have quantified the contribution of steric variations to global and regional sea-level change. However, the reported rates largely differ between studies. In this paper, we look at how the use of different temperature and salinity data sets can be one of the causes of the different estimates of steric sea-level change published so far. We also investigate how different methods (noise models) used to obtain the rate of change can be another source of different results. We find that the rate of change can vary up to 2 mm/year for the global mean as a result of different data sets and methods used. Regionally, differences can reach up to several tens of millimeters per year. We show that the noise models should always be carefully chosen for each region, so that the rate of change is accurately estimated.

Contemporary sea-level changes from global to local scales: a review

“…To give an order of magnitude, the WCRP Sea Level Budget Group [2] reports a rate of thermal expansion of 1.3 ± 0.4 mm yr −1 over 1993-2015 based on the ensemble mean of 11 different datasets. An update by Camargo et al [34], based on an ensemble mean of 10 datasets, indicates a value of 1.36 ± 0.1 mm yr −1 over 1993-2017 for the contribution of the 0-2000 m ocean depth layer (figure 5). The deep ocean contribution (below 2000 m) is assumed to be small so far, of the order of 0.1 mm yr −1 [28].…”

“…Details on these databases can be found in recent articles (e.g. among others, [–2,32,34]). To give an order of magnitude, the WCRP Sea Level Budget Group [2] reports a rate of thermal expansion of 1.3 ± 0.4 mm yr −1 over 1993–2015 based on the ensemble mean of 11 different datasets.…”

“…An update by Camargo et al . [34], based on an ensemble mean of 10 datasets, indicates a value of 1.36 ± 0.1 mm yr −1 over 1993–2017 for the contribution of the 0–2000 m ocean depth layer (figure 5). The deep ocean contribution (below 2000 m) is assumed to be small so far, of the order of 0.1 mm yr −1 [28].…”

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Figure 5Steric sea-level evolution for 1993–2017 based on different datasets. The black curve represents the ensemble mean of the considered datasets, and the grey shaded area the 1-sigma standard deviation (figure from [34]). (Online version in colour.

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Monthly Gravity Field Solutions From Early LEO Satellites' Observations Contribute to Global Ocean Mass Change Estimates Over 1993∼2004

“…The gridded steric sea-level change estimates of two situ datasets from Good et al (2013) (hereafter referred to as EN4) and Ishii and Kimoto (2009) (hereafter referred to as IK09) over the period January 1993 to December 2004 are adopted, which were recomputed by using the temperature and salinity datasets (0-2000 m) (Camargo et al, 2020). Taking the gridded steric sea-level change estimates from Camargo et al (2020), we compute the Global Mean Steric Sea Level (GMSSL) changes over global oceans at latitudes ranging 66°S to 66°N. As suggested by the World Climate Research Programme (WCRP) Sea Level Budget Group, the mean deep ocean steric sea level change between January 1993 and December 2004 is treated as 0.10 ± 0.10 mm/year (WCRP, 2018).…”