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reconstruction of an optimal tropical Indo-Pacific climate index (OTI), sup-
porting evidence for a tropical/North Pacific link extending as far west as the
western Indian Ocean. The coral-based reconstruction (1781-1993) shows the
twentieth-century regime shifts evident in the instrumental NPI and OTI, as
well as previous shifts. Changes in the strength of the correlation between
the NPI and OTI reconstructions over time, and the timing of regime shifts in
both series prior to the twentieth century, suggest a varying tropical influence
on North Pacific climate, with greater influence in the twentieth century. One
likely mechanism is the low-frequency variability of the El Niño/Southern
Oscillation (ENSO) and its varying impact on Indo-Pacific climate.
—R. D'Arrigo, G. Wiles, and R. Wilson
Box Fig. 7.2
Tree-ring-based reconstruction of the tropical Indo-Pacific climate index
(NPI): (
a
) actual and estimated December-May NPI for the 1900-1983 calibration period,
adf
adjusted degrees of freedom; (
b
) reconstruction of the December-May NPI from AD
1600 through 1983 based on North Pacific tree-ring data. The highlighted phase shifts were
identified by using intervention analysis (significant at the 90% confidence level; D'Arrigo
et al. 2005)
=
