Multi-proxy reconstructions of the North Atlantic Oscillation (NAO) Index: A critical review and a new well-verified winter NAO index reconstruction back to AD 1400

Abstract

The reconstruction of the North Atlantic Oscillation (NAO) index from high-resolution paleoclimate records is critically reviewed. In so doing, previously reported problems in most of the published NAO reconstructions are verified. A new multi-proxy reconstruction of the winter NAO index is developed, which largely corrects these reported problems, particularly the lack of reconstruction validity prior to 1850. It covers the period AD 1400-1979 and successfully verifies against independent estimates of the winter NAO index based on European instrumental and non-instrumental data as far back as 1500. This new success is due to a greatly expanded network of proxy records available for reconstruction. It also appears to be related to the use of an extended reconstruction model calibration period that reduced an apparent bias in selected proxies associated with the effect of anomalous 20th century NAO variability on climate teleconnections over circum-North Atlantic land areas.