highly significantP < 0.001
For each index, we calculated and tested the correlation between the reconstructions based on tree-ring data and contemporary indices, which proved to be highly significant in each case (for AMO indices: F 1,104 = 268.6, R 2 adj = 0.72, P < 0.001; for NAO indices: F 1,15 = 70.0, R 2 adj = 0.81, P < 0.001); old and recent indices were therefore averaged per year over common periods and combined into a single index.