Multiproxy reconstructions of the North Atlantic oscillation

Multiproxy composite reconstructions of North Atlantic Oscillation (NAO) indices are presented spanning the last three centuries. These composite time series draw on four nearly independent reconstructions derived from different combinations of global and North Atlantic sector climate proxy data (e.g., tree rings and ice cores) as well as long instrumental records. A composite reconstruction based on all four series (R4) extends from 1750 to 1979, while another version based on only three series (R3) extends from 1701 to 1979. Both composite reconstructions outperform the individual series based on correlation and verification statistics. These results suggest that each individual series reflects different aspects of the NAO, such that when combined, they yield more robust reconstructions. As to be expected, these composite reconstructions, based on both proxy and long instrumental data, yield more optimal results than individual or composite reconstructions based on proxy data alone. The reconstructions presented here provide an improved means of addressing features evident in the instrumental record with respect to those of prior centuries. One such feature evident in the reconstructions is an apparent increase in variance in the instrumental period relative to the past record.