Evaluation of temperature in RCA3 over Europe during the last Millennium

An evaluation of the regional climate model RCA3, based on comparisons of model results with proxy data and observational data, showed poor agreement between these data series. This is probably a consequence of deficiencies and error margins in the proxy reconstructions, which is why more high quality proxy data needs to be developed. Model errors, uncorrelated internal variability and simplified treatment of forcing conditions also contribute to the discrepancies.

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.

Torneträsk, proxy temperature
Figure 1. Poor agreement between model data and reconstructed spring- and summer temperature during the time period 1000-2004. The reconstruction is based on analysis of the width and density in the summer wood in fossil-and living pine, in the area around Torneträsk in northern Sweden, produced by Grudd (2008). The graph shows temperature anomalies of the average temperature 1961-90; unfiltered/filtered data with a running mean of 30 years: blue/black. Correspondent data for RCA3 is shown in red/green. The warmest/coldest 100-year period according to the definition of the proxy data is shown with orange/yellow.
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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.