Reconstructing the history of the past
Historical documents and climate modelling provide us with powerful tools and important knowledge about past environmental conditions that are essential to our
understanding of climate but also our history. Although documents is a great source of knowledge about the climate and its effects on society, climate models can
enhance our knowledge by giving us an opportunity to re-analyze past conditions. One field where climate modelling may provide greater insight is in oceanography.
Measurements of the ocean over long periods are rare and ocean models can therefore complement our understanding. In Figure 1 we show how results from an
ocean model can reproduce the sea surface temperature (SST) of various parts of the Baltic Sea. Over periods and for regions where we have a high sampling frequency
of the measurements we validate our models. Over periods when the measurements become sparser, for example in the Bothnian Bay (see Figure 1, bottom panel), we are
presented with a suggestion of the environmental conditions for that time.
(Click image to enlarge)
Figure 1. Measured (circles) and modelled (line) sea surface temperatures from three different sub-basins in the Baltic Sea.
In a recent study by Eriksson et al. (2007a) we have characterized past climate based on available data. By using statistical methods 15 major climate periods over the past 500 years were
identified, see Figure 2. These periods range from cold periods to the present day warming. It was also found that cold periods have larger variability than mild periods.
(Click image to enlarge)
Figure 2. Characterizing the European sub-arctic winter climate since 1500 (from Eriksson et al., 2007a).
The work of Eriksson et al. (2007a) formed the foundation for the modeling efforts by Hansson and Omstedt (2008), who tried to reproduce the 15 climate periods in a realistic way using models.
From this a greater insight into the horizontally and vertically integrated ocean temperatures and maximum ice extent over the past 500 years was gained, see Figure 3. At the products section
of our home page supporting material for last 50, 100 and 500 years are made freely available.
(Click image to enlarge)
Figure 3. Modelled maximum ice extent and mean winter temperature (from Hansson and Omstedt, 2008).
Our present research work continues on this path by looking closer on river run-off (eg. Eriksson et al., 2007b), salinity, oxygen and acid-base (pH) balance over the Baltic Sea history.
References:
- Eriksson, C., D. Hansson, A. Omstedt and D. Chen , 2007b. Reconstruction of river runoff to the Baltic Sea for the period 1500–1995. GEWEX Newsletter, Vol 17, No 3.
- Eriksson, C., Omstedt, A., Overland, J.,E., Percival, D.,B., and H.,O., Mofjeld, 2007a. Characterizing the European subarctic winter climate since 1500 using ice, temperature, and atmospheric circulation time series. Journal of Climate 20, 5316-5334. DOI 10.1175/2007JCLI1461.
- Hansson, D., and A., Omstedt, 2008.Modelling the Baltic Sea ocean climate on centennial time scales; Temperature and Sea Ice. Climate Dynamics 30, 763-778. DOI 10.1007/s00382-007-0321-2.
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