Calibration Uncertainties of Tropical Pacific Climate Reconstructions over the Last Millennium

Abstract

Several climate field reconstruction methods assume stationarity between the leading patterns of variability identified during the instrumental calibration period and the reconstruction period. We examine how and to what extent this restrictive assumption may generate uncertainties in reconstructing past tropical Pacific climate variability. Based on the Last Millennium (850–2005 CE) ensemble simulations conducted with the Community Earth System Model and by developing a series of pseudoproxy reconstructions for different calibration periods, we find that the overall reconstruction skill for global and more regional-scale climate indices depends significantly on the magnitude of externally forced global mean temperature variability during the chosen calibration period. This effect strongly reduces the fidelity of reconstructions of decadal to centennial-scale tropical climate variability, associated with the interdecadal Pacific oscillation (IPO) and centennial-scale temperature shifts between the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). In contrast, our pseudoproxy-based analysis demonstrates that reconstructions of interannual El Niño–Southern Oscillation (ENSO) variability are more robust and less affected by changes in calibration period.

Sources of Nonergodicity for Teleconnections as Cross‐Correlations

“…Given that the reconstruction $${r}_{L}^{{\bullet}}$$ is a function of variables featuring no or considerably less serial correlation, it might be suitable for assessing the significance of the forced changes of r L . The results of Yun and Timmermann (2019) suggest that r L changes considerably more than r H .…”

“…Lee under IBS‐R028‐D1. T. Bódai thanks Jan Vrbik for useful discussions about the Fisher transformation and possible improvements; Kyung‐Sook Yun for calling his attention to Yun and Timmermann (2019) on high‐ and low‐frequency ENSO teleconnections; and Gábor Drótos for many useful discussions and feedback on the manuscript. We are grateful to the Indian Institute of Tropical Meteorology for providing the AISMR data (Parthasarathy et al., 1994; Indian Institute of Tropical Meteorology, n.d.), and to the NOAA ESRL Physical Sciences Laboratory for providing the Niño 3 time series (Rayner et al., 2003; NOAA ESRL Physical Sciences Laboratory, n.d.).…”