Evaluation of a reconstruction of winter and summer temperatures in the low countries, AD 764-1998

A new reconstruction of winter and summer temperatures in the Low Countries (the present-day Netherlands and Belgian Flanders), based upon documentary evidence from AD 764 to 1705 and extended by observations to 1998, is compared with relevant paleo series from the European network. The Low Countries Temperature (LCT) reconstruction is well supported by existing evidence in both seasons from about 1300 onwards, on timescales ranging from annual to centennial. The spectral analysis confirms that the dominant oscillations in the LCT have counterparts in the independent data and that most of the periodicities characteristic for the instrumental segment of the LCT are preserved in the reconstruction. Throughout this period of reliable reconstruction there was no detectable inhomogeneity of the variances in either seasons. Prior to about 1300, there are few sources that can be used to evaluate LCT. It was possible to add some support for the LCT on decadal and centennial timescales for the 12th and 13th centuries. However, there is no independent data for the first three centuries of the reconstruction. The LCT series exhibits significant season-dependent variability on bidecadal and centennial timescales. The seasonality is particularly remarkable in the 10th and 15th centuries which were - on average - warm in the summer and cold in the winter. The 20th century was by far (three standard errors) the warmest century of the last millennium in terms of winter temperatures, while the 13th century was warmest in terms of summer temperatures (by the narrow margin of one standard error). In both seasons, the coldest centennial period was centered around 1600. The present results place the reconstructed LCT series within the existing paleoclimatic network, and provide an insight into temperature variability in the Low Countries through the centuries.