Fig. 2: Wavelet analysis of the bristlecone pine ¹⁴C series.

Shades denote the dimensionless continuous wavelet transform power-spectrum density. The color bar placed on the right represents the squared power of the wavelet transform and the numbers indicate the spectrum power level (dimensionless). High values in a few time intervals (x-axis) with some periodicity (y-axis) show that the amplitude of a signal with that periodicity emerges from noise in those years. The black contour denotes the 5% significance level against red noise. The area where edge effect influence distorts the picture is shown in lighter shades. The signal attributable to solar the solar cycle is marked with yellow fields. The black line outlines the variance significant relative to red noise. A similar result can be obtained for the European Oak series (shown in Supplementary Fig. 1).