Pacific decadal variability over the last 2000 years and implications for climatic risk

The Interdecadal Pacific Oscillation, an index which defines decadal climate variability throughout the Pacific, is generally assumed to have positive and negative phases that each last 20-30 years. Here we present a 2000-year reconstruction of the Interdecadal Pacific Oscillation, obtained using information preserved in Antarctic ice cores, that shows negative phases are short (7 +/- 5 years) and infrequent (occurring 10% of the time) departures from a predominantly neutral-positive state that lasts decades (61 +/- 56 years). These findings suggest that Pacific Basin climate risk is poorly characterised due to over-representation of negative phases in post-1900 observations. We demonstrate the implications of this for eastern Australia, where drought risk is elevated during neutral-positive phases, and highlight the need for a re-evaluation of climate risk for all locations affected by the Interdecadal Pacific Oscillation. The initiation and future frequency of negative phases should also be a research priority given their prevalence in more recent centuries. Negative phases of the Interdecadal Pacific Oscillation, which alters hydroclimatic risk across the Pacific, have been shorter and less frequent than inferred from the instrumental record, suggests a 2,000-year ice core reconstruction.

Automated summary

A 2000-year reconstruction of the Interdecadal Pacific Oscillation based on Antarctic ice cores reveals that negative phases are shorter and less frequent than previously believed. This suggests that the characterization of climate risk in the Pacific Basin is inaccurate, and a re-evaluation is needed for all affected areas.