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151.3.4.1 Sea Level

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WGI AR5 Fig1-10

Figure 1.10 Estimated changes in the observed global annual mean sea level (GMSL) since 1950 relative to 1961–1990. Estimated changes in global annual sea level anomalies are presented based on tide gauge data (warm mustard: Jevrejeva et al., 2008;[1] dark blue: Church and White, 2011;[2] dark green: Ray and Douglas, 2011)[3] and based on sea surface altimetry (light blue). The altimetry data start in 1993 and are harmonized to start from the mean 1993 value of the tide gauge data. Squares indicate annual mean values and solid lines smoothed values. The shading shows the largest model projected range of global annual sea level rise from 1950 to 2035 for FAR (Figures 9.6 and 9.7 in Warrick and Oerlemans, 1990)[4], SAR (Figure 21 in TS of IPCC, 1996), TAR (Appendix II of IPCC, 2001) and for Church et al. (2011[2]) based on the Coupled Model Intercomparison Project Phase 3 (CMIP3) model results not assessed at the time of AR4 using the SRES B1, A1B and A2 scenarios. Note that in the AR4 no full range was given for the sea level projections for this period. Therefore, the figure shows results that have been published subsequent to the AR4. The bars at the right-hand side of the graph show the full range given for 2035 for each assessment report. For Church et al. (2011)[2] the mean sea level rise is indicated in addition to the full range. See Appendix 1.A for details on the data and calculations used to create this figure.

Global mean sea level is an important indicator of climate change (Section 3.7 and Chapter 13). The previous assessments have all shown that observations indicate that the globally averaged sea level is rising. Direct observations of sea level change have been made for more than 150 years with tide gauges, and for more than 20 years with satellite radar altimeters. Although there is regional variability from non-uniform density change, circulation changes, and deformation of ocean basins, the evidence indicates that the global mean sea level is rising, and that this is likely (according to AR4 and SREX) resulting from global climate change (ocean warming plus land ice melt; see Chapter 13 for AR5 findings). The historical tide gauge record shows that the average rate of global mean sea level rise over the 20th century was 1.7 ± 0.2 mm yr–1 (e.g., Church and White, 2011).[2] This rate increased to 3.2 ± 0.4 mm yr–1 since 1990, mostly because of increased thermal expansion and land ice contributions (Church and White, 2011;[2] IPCC, 2012b).[5] Although the long-term sea level record shows decadal and multi-decadal oscillations, there is evidence that the rate of global mean sea level rise during the 20th century was greater than during the 19th century.

All of the previous IPCC assessments have projected that global sea level will continue to rise throughout this century for the scenarios examined. Figure 1.10 compares the observed sea level rise since 1950 with the projections from the prior IPCC assessments. Earlier models had greater uncertainties in modelling the contributions, because of limited observational evidence and deficiencies in theoretical understanding of relevant processes. Also, projections for sea level change in the prior assessments are scenarios for the response to anthropogenic forcing only; they do not include unforced or natural interannual variability. Nonetheless, the results show that the actual change is in the middle of projected changes from the prior assessments, and towards the higher end of the studies from TAR and AR4.

NotesEdit

  1. Jevrejeva, S., J. C. Moore, A. Grinsted, and P. L. Woodworth, 2008: Recent global sea level acceleration started over 200 years ago? Geophys. Res. Lett., 35, L08715.
  2. 2.0 2.1 2.2 2.3 2.4 Church, J. A., J. M. Gregory, N. J. White, S. M. Platten, and J. X. Mitrovica, 2011: Understanding and projecting sea level change. Oceanography, 24, 130–143. Cleveland, W. S., 1979: Robust locally weighted regression and smoothing scatterplots. J. Am. Stat. Assoc., 74, 829–836.
  3. Ray, R. D., and B. C. Douglas, 2011: Experiments in reconstructing twentieth-century sea levels. Prog. Oceanogr., 91, 496–515.
  4. Warrick, R., and J. Oerlemans, 1990: Sea level rise. In: Climate Change: The IPCC Scientific Assessment [J. T. Houghton, G. J. Jenkins and J. J. Ephraums (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 261–281.
  5. IPCC , 2012b: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. Special Report of the Intergovernmental Panel on Climate Change. [ Field, C. B., V. Barros, T. F. Stocker, D. Qin, D. J. Dokken, K. L. Ebi, M. D. Mastrandrea, K. J. Mach, G.-K. Plattner, S. K. Allen, M. Tignor, and P. M. Midgley (Eds.)]. Cambridge University Press, Cambridge, United Kingdom, 582 pp.
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