Abstract
AbstractRecent 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.
Highlights
The oceans are a major reservoir of heat and have stored about 90% of the human‐induced heat in the climate system over the last 50 years (MacIntosh et al, 2017; von Schuckmann et al, 2016)
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 leads to the most representative uncertainty
We describe how we calculated steric sea‐level change (SLC) and the ocean temperature and salinity data sets used in section 2, followed by an explanation of the noise models used to compute the trends and uncertainties
Summary
The oceans are a major reservoir of heat and have stored about 90% of the human‐induced heat in the climate system over the last 50 years (MacIntosh et al, 2017; von Schuckmann et al, 2016). The resulting ocean warming leads to sea‐level change (SLC), which is an important reflection of how the oceans respond to global warming (Kopp et al, 2016). This process, known as thermosteric SLC, is the dominant component of the steric contribution to global mean sea‐level (GMSL) change. Steric SLC is partially driven by salinity variations (i.e., halosteric change). Halosteric SLC can be just as important as thermosteric changes, or even the dominant process of steric sea‐level variations, for instance, in polar regions (Stammer et al, 2013). Studies of steric contributions to regional SLC should consider both salinity and temperature variations (MacIntosh et al, 2017)
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