Long term sea level change in the instrumental period
- This page is part of the topic Antarctic climate and environment change in the instrumental period
The first three assessment reports of the IPCC arrived at similar conclusions with regard to global sea level change during the Twentieth Century. For example, the third report (Church et al., 2001) concluded that global sea level had changed within a range of uncertainty of 1-2 mm/yr. Since then, there have been major workshops (e.g. World Climate Research Programme workshop on Sea Level Rise and Variability, Church et al., 2007), reviews by individual scientists (e.g. Woodworth et al., 2004), and, most recently, the publication of the ocean climate and sea level change chapter within the IPCC Fourth Assessment Report (Bindoff et al., 2007). A consensus seems to have been achieved that the Twentieth Century rise in global sea level was closer to 2 than 1 mm/year, with values around 1.7 mm/yr having been obtained for the second half of the last century in the most recent studies (e.g. Church et al., 2004; Holgate and Woodworth, 2004). However, it should be noted that the Antarctic contribution to sea level now is small compared to what it was following the LGM Transition and through the Holocene.
Fluctuations in the size of Antarctic and Greenland ice sheets during the glacial/interglacial cycles resulted in sea level variations of over 120 m. However, in spite of the enormous sea level-equivalent of the ice stored in the two ice sheets (Table 11.3 of Church et al., 2001), both seem to have played relatively minor roles in sea level change during the last two centuries. The major contributions to Twentieth Century sea level rise are believed to have originated from ocean thermal expansion and the melting of glaciers and ice caps. Antarctica’s contribution appears to have been of the order of 0.1-0.2 mm/yr over the last few decades with some evidence for a slightly larger value in the 1990s (Bindoff et al., 2007).
The most recent data (i.e. from the 1990-2000s) from tide gauges and satellite altimeters suggest that global sea level is now rising at a rate of 3 mm/yr or more (e.g. Holgate and Woodworth, 2004; Beckley et al., 2007). The IPCC’s 4th Assessment Report cites 3.1 mm/yr for 1993-2003 (IPCC, 2007). However, according to Cazenave et al., (2009), and based on GRACE and altimetric satellite data and Argo ocean float data from 2003-2008, the rate has slowed to 2.5 mm/yr; this reflects a significant slow down in the thermosteric component, balanced by an increase in ice contributions (half from mountain glaciers and half from ice sheets). This is still a higher rate than typical for the Twentieth Century. As pointed out by Milne (2009) the latest results are not the last word and we need longer time series to be confident in the magnitude of the trend.
Figure 4.45 shows a time series of annual mean sea level values from Vernadsky, suggesting an upward trend (uncorrected for local land movements) of 1.6 ± 0.4 mm/year, with a dip in the 1970s for which one has to be concerned about instrumental problems, and no evidence for recent acceleration. As an aside, one may note that observed Southern Hemisphere Twentieth Century sea level trends tend to be generally lower than Northern Hemisphere ones (e.g. see the long southern records studied by Hunter et al., 2003 and Woodworth et al., 2005).
- Church, J.A., Gregory, J.M., Huybrechts, P., Kuhn, M., Lambeck, K. Nhuan, M.T., Qin, D. and Woodworth, P.L. 2001. Changes in sea level. In Climate change 2001: the scientific basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, J.T. Houghton, Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell and C.A. Johnson, eds. Cambridge University Press, Cambridge, 881pp.
- Church, J., Wilson, S., Woodworth, P. and Aarup, T. 2007. Understanding sea level rise and variability. Meeting report. EOS Transactions of the American Geophysical Union, 88(4), 23 January 2007, 43.
- Woodworth, P.L., Gregory, J.M. and Nicholls, R.J. 2004. Long term sea level changes and their impacts, 715-753 (chapter 18) in The Sea, 13, edited by A.R. Robinson and K.H. Brink. Harvard University Press.
- Bindoff, N., Willebrand, J., Artale, V., Cazenave, A., Gregory, J., Gulev, S., Hanawa, K., Le Quéré, C., Levitus, S., Nojiri, Y., Shum, C., Talley, L. and Unnikrishnan, A. 2007. Observations: oceanic climate change and sea level. In Climate Change 2007: The Physical Science Basis. Contribution of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (eds. S. Solomon, D. Qin, and M. Manning). Cambridge University Press. United Kingdom and New York, NY, USA.
- Church, J.A., White, N.J., Coleman, R., Lambeck, K. and Mitrovica, J.X. 2004. Estimates of the regional distribution of sea-level rise over the 1950 to 2000 period, Journal of Climate, 17, 2609-262.
- Holgate, S.J. and Woodworth, P.L. 2004. Evidence for enhanced coastal sea level rise during the 1990s, Geophysical Research Letters, 31, L07305, doi:10.1029/2004GL019626.
- Beckley, B.D., Lemoine, F.G., Lutchke, S.B., Ray, R.D. and Zelensky, N.P. 2007. A reassessment of global and regional mean sea level trends from TOPEX and Jason-1 altimtery based on revised reference frame and orbits, Geophysical Research Letters, 34, L14608, doi:10.1029/2007GL030002.
- IPCC 2007. Climate Change 2007: The Physical Science Basis. Contribution of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge.
- Milne, G.A. 2009. Using models to inform the field community: Far-field sea level data applications, PAGES News, 17, No 2 June 2009, 56-57.
- Hunter, J., Coleman, R. and Pugh, D. 2003 The sea level at Port Arthur, Tasmania, from 1841 to the present, Geophysical Research Letters, 30, 1401, doi:10.1029/2002GL016813.
- Woodworth, P.L., Pugh, D.T., Meredith, M.P. and Blackman, D.L. 2005. Sea level changes at Port Stanley, Falkland Islands, Journal of Geophysical Research, 110, C06013, doi:10.1029/2004JC002648.