Original study: Messié, M. and F.P. Chavez, 2011: Global modes of sea surface temperature variability in relation to regional climate indices. (mbari.org)
They found the answer in the leading pattern of sea surface temperature variability in the North Pacific: the PDO. (sciencedaily.com)
Laepple, T. & Huybers, P. Ocean surface temperature variability: large model — data differences at decadal and longer periods. (nature.com)