Fig. 2.

The DLH tree-ring δ¹⁸O chronology. (A) Visualization of all 44 δ¹⁸O measurement series. (B) DLH δ¹⁸O chronology (navy blue line), third-order polynomial fitting of this chronology (thick black line), and July solar insolation between 30°N and 60°N (red line). The gray shading indicates the 95% CI of the composite δ¹⁸O chronology. For better comparison, the y-axis of the δ¹⁸O chronology was reversed. (C) Sample depth (with the black line indicating the number of trees in the pooled series) of the DLH δ¹⁸O chronology and Rbar (gray line) and EPS (purple line) of the δ¹⁸O dataset, calculated over a 250-y window in steps of 1 y. The Rbar time series was smoothed with a 100-y Gaussian-weighted filter. The annual values with EPS ≥ 0.85 accounts for 80.2% during 3250 BCE to 2011 CE, whereas 91.2% of values have EPS ≥ 0.25 and 37.7% are ≥ 0.50 before 3250 BCE.