RCA3 has recently been set up and run for the last Millennium (AD 951-1998) (Shimanke et al. 2011). Here, we report on an evaluation, to find how well it reproduces the near-surface temperature climate in Europe. The evaluation was performed by Malin Friis, student at the Department of Ecology and Environmental Science of Umeå Univeristy, for her bachelor thesis in Earth Science (Friis 2012).
Comparison of results from RCA3 to proxy data and observational data
Results from RCA3 were compared to five proxy-based temperature reconstructions and to observational data from Scandinavia and the Alpine region, with respect to average temperatures, variability and correlation. The proxy series represented different proxy types and seasons and they came from both nearby and distant sites, most of them with yearly resolution. The utility of the reconstructions was tested by comparison to instrumental temperature observations from the Climate Research Unit from AD 1901-2009. Correlation analysis was performed between proxy data from nearby and distant sites and so were correlation analysis between model data and observational data.
Discrepancies between the proxy series
Comparison of proxy data and observational data showed that not only temperature explains the variability in the proxy series. The correlations between the proxy series from both nearby and distant sites were weak, which indicated different development of temperatures over time. On the contrary, both temperature observations and model results showed a high degree of correlation between the locations in the proxy series.
Poor agreement between model data and proxy data
The agreement between proxy data and model data was poor. RCA3 showed lower temperatures in comparison to all the reconstructions. Although the RCA3 simulation in general showed a warm period in the first centuries (a.k.a the Medieval Climate Anomaly) and later a cold period corresponding to the Little Ice Age the timing of these events differed from that retrieved from the proxy-based reconstructions.
The warmest 100-year period in RCA3 never coincided with the warmest 100-year period in the reconstructions, and the coldest periods only coincided in two cases. Figure 1 illustrates the results of the comparison of model data to the one of the proxy data series, from Torneträsk in northern Sweden.
More proxy data needs to be developed
Given the limited number of proxy-based reconstructions used here, one can not give a clear picture of the temperature development in Europe during the last Millennium. The results indicate that if the model’s representation of the temperature climate is to be evaluated, a larger number of high-quality proxy-based reconstructions is needed. The fact that this evaluation does not give any clear answers to how well the model can reproduce the European temperature climate during the last Millennium indicates that a continued evaluation and a development of evaluation methods are very important.
Friis, M. 2012. European temperature climate during the last Millennium: A comparison of results from a regional climate model with proxy data and observational data. Umeå University.
Grudd, H. 2008. Torneträsk tree-ring width and density AD 500-2004: a test of climatic sensitivity and a new 1500-year reconstruction of north Fennoscandian summers. Climate dynamics: 31:843-857.
Shimanke, S., Kjellström, E., Strandberg, G., Meier, M.H.E. 2011. A regional climate model simulation over the Baltic Sea region for the last Millennium. Reports Oceanography 111, SMHI.