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Time of emergence for regional sea-level change


Determining the time when the climate change signal from increasing greenhouse gases exceeds and thus emerges from natural climate variability (referred to as the time of emergence, ToE) is an important climate change issue1. Previous ToE studies were mainly focused on atmospheric variables2,3,4,5,6,7. Here, based on three regional sea-level projection products available to 2100, which have increasing complexity in terms of included processes, we estimate the ToE for sea-level changes relative to the reference period 1986–2005. The dynamic sea level derived from ocean density and circulation changes alone leads to emergence over only limited regions. By adding the global-ocean thermal expansion effect, 50% of the ocean area will show emergence with rising sea level by the early-to-middle 2040s. Including additional contributions from land ice mass loss, land water storage change and glacial isostatic adjustment generally enhances the signal of regional sea-level rise (except in some regions with decreasing total sea levels), which leads to emergence over more than 50% of the ocean area by 2020. The ToE for total sea level is substantially earlier than that for surface air temperature and exhibits little dependence on the emission scenarios, which means that our society will face detectable sea-level change and its potential impacts earlier than surface air warming.

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Figure 1: Standard deviation of annual sea level.
Figure 2: Multimodel ensemble median ToE for regional sea-level change and the 16–84% range under RCP8.5.
Figure 3: The cumulative fraction of the total area with the emergence of change signals before the given time from the multimodel ensemble median patterns.
Figure 4: Multimodel ensemble mean projections of global mean thermosteric sea level (GMTSL) and global mean surface air temperature (GMSAT) under RCP4.5 and RCP8.5.


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We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups for producing and making available their model output. For CMIP, the US Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and leads development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. We thank AVISO ( for providing altimeter data. We also thank D. Monselesan for help with CMIP5 data handling. Detailed comments on an early draft by M. King and J. Hunter helped to improve the manuscript significantly. J.A.C. and X.Z. are supported by the Australian Climate Change Science Program (ACCSP). K.L. and J.H. are supported by the China Scholarship Council and the National Natural Science Foundation of China (41276006). A.B.A.S. is funded by a CSIRO Office of the Chief Executive Postdoctoral Fellowship.

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X.Z. conceived and designed the study with K.L. K.L. carried out the analysis and produced all figures under the guidance of X.Z. and J.A.C. A.B.A.S. prepared the regional sea-level projection data for land ice and groundwater contributions. K.L. wrote the first draft with X.Z., and all authors made contributions to writing the manuscript.

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Correspondence to Xuebin Zhang.

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Lyu, K., Zhang, X., Church, J. et al. Time of emergence for regional sea-level change. Nature Clim Change 4, 1006–1010 (2014).

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