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Published March 16, 2018 | Published + Supplemental Material
Journal Article Open

Disentangling global warming, multi-decadal variability, and El Niño in Pacific temperatures

Abstract

A key challenge in climate science is to separate observed temperature changes into components due to internal variability and responses to external forcing. Extended integrations of forced and unforced climate models are often used for this purpose. Here we demonstrate a novel method to separate modes of internal variability from global warming based on differences in time scale and spatial pattern, without relying on climate models. We identify uncorrelated components of Pacific sea surface temperature variability due to global warming, the Pacific Decadal Oscillation (PDO), and the El Niño–Southern Oscillation (ENSO). Our results give statistical representations of PDO and ENSO that are consistent with their being separate processes, operating on different time scales, but are otherwise consistent with canonical definitions. We isolate the multidecadal variability of the PDO and find that it is confined to midlatitudes; tropical sea surface temperatures and their teleconnections mix in higher‐frequency variability. This implies that midlatitude PDO anomalies are more persistent than previously thought.

Additional Information

© 2018 American Geophysical Union. Received 6 NOV 2017; Accepted 17 JAN 2018; Accepted article online 25 JAN 2018; Published online 15 MAR 2018. We thank T. Kohyama, K. Armour, T. Bischoff, M. Stuecker, and K.‐K. Tung for valuable conversations and feedback on this work. R. C. W. and D. L. H. acknowledge support from the National Science Foundation (grant AGS‐1549579). R. C. W. and D. S. B. acknowledge support from the Tamaki Foundation. The data sets used are documented in Smith et al. (2008) and Compo et al. (2011).

Attached Files

Published - Wills_et_al-2018-Geophysical_Research_Letters.pdf

Supplemental Material - 2017GL076327-sup-0003-Text_SI-S01_AA.pdf

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