Seasonality of low-frequency variability in early-instrumental European temperatures.

The seasonality of low-frequency temperature variability is studied by application of multichannel singular spectrum analysis to 7 long early-instrumental European temperature records. Focus is on timescales longer than 50 years. We find that the temporal pattern of low-frequency variability is clearly season-dependent. Opposing winter/summer tendencies result in a weak variability on timescales longer than 50 yr in the annual-mean data. Summer temperature variations seem to exhibit a preferential timescale in the range 60-80 years. An oscillation with this timescale is found to be significant against red noise surrogates when analysing 4 long European paleo proxy records for summer temperature. The present results stress the necessity of using seasonally homogeneous datasets of paleo proxies for reconstructing low-frequency variability patterns.