Patterns of temperature variability on multidecadal to centennial timescales

Abstract

The spatiotemporal structure of low‐frequency temperature variability, as reflected in a paleonetwork covering the North American and European domains, is studied using a combination of statistical techniques including principal component analysis and univariate and multivariate singular spectrum analysis. On timescales τ longer than 50 years, two statistically significant modes of temperature variability are identified, one on multidecadal timescale and one on centennial timescale. The first mode is oscillatory, with τ in the narrow range 60–80 years. The spatial pattern of this multidecadal mode implies coherent oscillations over Europe and over northeastern North America, with maximum amplitudes in Europe; over northwestern North America this mode is absent. Its geographic shape suggests a connection to the North Atlantic Oscillation; a relation with solar forcing could not be detected. The second mode, which dominates low‐frequency variability at high latitudes, describes temperature variations in a wide interval of timescales (τ>100 years); in the longest records a weak ∼120 year oscillation can be identified with confidence. The temporal pattern of the centennial mode shows a multiple phase “Little Ice Age” and a prolonged “Medieval Warm Period.” The interpretation of centennial mode is difficult given its rather variable large‐scale pattern and the uncertainty associated with centennial timescales in the data. The present data set gives indications that in North America, centennial variability is independent of season, while the multidecadal mode might exhibit seasonally dependent features. In Europe, both low‐frequency modes of temperature variability are season specific.