Initialized Decadal Prediction for Transition to Positive Phase of the Interdecadal Pacific Oscillation and Resumption of Larger Rates of Global Warming

Retrospective hindcasts have shown skill in simulating the two phase changes of the Interdecadal Pacific Oscillation (IPO) since 1960, the first from negative to positive in the 1970s, and the second from positive to negative in the late-1990s (Meehl and Teng, 2012, 2014a). A proposed mechanism for IPO multidecadal variability indicates that for such decadal transitions to occur, there should be a build-up of heat content in the off-equatorial western tropical Pacific. An ENSO event can then trigger the transition of tropical Pacific SSTs to the opposite IPO phase (Meehl and Hu 2006; Farneti et al 2013). Evidence is shown that for the two phase changes of the IPO since 1960, the ocean initial state for the mid-1970s shift showed high values of off-equatorial western Pacific heat content, while for the late-1990s transition there were low heat content values. Elements of the 1976-77 El Nino and 1998-2000 La Nina where simulated in the hindcasts and likely contributed to the IPO transitions. Western Pacific heat content has subsequently built up again, and a decadal prediction initialized in 2013 shows that the Nino3.4 SSTs have tracked the observations through mid-2015. The year 3-7 average prediction (2015-2020) from the 2013 initial state shows a transition to the positive phase of the IPO from the previous negative phase, and a resumption of larger rates of global warming consistent with the positive IPO phase.