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DESCRIPTION OF THE SEA LEVEL SCENARIOS

On average the global sea level has risen by about 10 - 20 cm during the past century, but in Finland the land is still rising following the disappearance of ice after the last glaciation. The net effect has been a fall in relative sea level. This fall has slowed in recent decades, but this is probably a regional effect in the Baltic Sea of changes in wind climate, as similar trends are not evident on Atlantic coasts. Previous projections suggest that accelerated global sea level rise may reverse the historical downward trend on the southern coast of Finland. Are these projections still valid? And how would possible future changes in atmospheric pressure or in storm intensity affect the risk of coastal inundation?

Summary table

Summary information about the methods used to derive the sea level scenarios
Underlying global drivers SRES storylines
Time horizon 21st century
Baseline 2000
Methods Combination of the global mean annual sea level, the land uplift and a regression equation with the North Atlantic Oscillation (NAO) index
Models used -
Scenario area Finnish coastline
Main input data Global mean sea level and NAO estimated by climate models
Output variables Sea-level rise
Output resolution Individual sites along the Finnish coastline

Details

The FINSKEN sea level scenarios were constructed as a combination of three factors, the global mean sea level, the absolute land uplift, and the North Atlantic Oscillation (NAO) index, that can be used as a surrogate for the water balance of the Baltic Sea.

The study was based on sea level observations (4-hour intervals) from 13 Finnish tide gauges suitable for studies of long-term changes. The trend in the time-series has been investigated. The absolute land uplift rates have been calculated by combining the relative land uplift rates (based on the observed sea level) and the global mean sea level rise.

The water balance of the Baltic Sea plays an important role in determining the mean sea level. The total water volume inside the semi-enclosed sea can vary and is thus responsible for a sea level difference of approximately one meter. These water balance variations do not even out at an annual time scale, and they explain most of the year-to-year variability of annual mean sea levels. The sea level variability at the Finnish coast has been found to correlate with the North Atlantic Oscillation (NAO) index (Kahma 1999, Johansson et al. 2001), and is utilized with a linear regression for the FINSKEN scenarios.

The scenario calculation was done by applying scenarios of global mean sea level and of the NAO index to the found relationships. Estimates of the global mean sea level for the 21st century were taken from the Third Assessment Report of the IPCC (Church et al. 2001), based on the SRES emission scenarios. According to these scenarios, the global mean sea level will rise 9-88 cm from the level of 1990 up to the year 2100. Future scenarios for the NAO index were obtained from different atmosphere-ocean general circulation models (AOGCMs).

A summary of the sea level related results of FINSKEN in Finnish is available from the web page of FIMR.

Literature cited

  • Church J.A., Gregory J.M., Huybrechts P., Kuhn M., Lambeck K., Nhuan M.T., Qin D. & Woodworth P.L. 2001. Changes in Sea Level. In: Houghton J.T., Ding Y., Griggs D.J., Noguer M., van der Linden P.J., Dai X., Maskell K. & Johnson C.A. (eds.), Climate Change 2001: The scientific basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 639-693.
  • Johansson M., Boman H., Kahma K.K. & Launiainen J. 2001. Trends in sea level variability in the Baltic Sea. Boreal Env. Res. 6: 159--179.
  • Kahma, K. 1999. Atlantin ilmanpaine vaikuttaa Itämereen [NAO is reflected in the Baltic sea level]. Finnish Institute of Marine Research, Annual Report 1999.

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Updated 13.05.2004, Stefan Fronzek
Finnish Environment Institute (SYKE) | Research Programme for Global Change (GTO)

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