Increase in sea level variability with ocean warming associated with the nonlinear thermal expansion of seawater

Global sea levels are rising in part due to the expansion of seawater with increasing temperatures. Since the rate, or coefficient, of thermal expansion increases with greenhouse warming seawater density becomes increasingly sensitive to higher temperatures; thereby contributing to observed and future projections of accelerating sea level rise. So far unexplored is how the nonlinear thermal expansion property of seawater will affect the variability of future higher sea levels. Sea level variability increasingly contributes to coastal flooding and erosion as global sea levels rise, partly due to the thermal expansion of seawater, which accelerates with increasing temperature. Climate model simulations with increasing greenhouse gas emissions suggest that future sea level variability, such as the annual and interannual oscillations that alter local astronomical tidal cycles and contribute to coastal impacts, will also increase in many regions.

In this study, Matthew J. Widlansky present an analysis of the CMIP5 climate model projections of future sea level to show that there is a tendency for a near-global increase in sea level variability with continued warming that is robust across models, regardless of whether ocean temperature variability increases. Specifically, for an upper-ocean warming by 2 °C, which is likely to be reached by the end of this century, sea level variability increases by 4 to 10% globally on seasonal-to-interannual timescales because of the nonlinear thermal expansion of seawater. As the oceans continue to warm, future ocean temperature oscillations will cause increasingly larger buoyancy-related sea level fluctuations that may alter coastal risks.

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