Decadal Climate Variability in the Pacific

Abstract:The Interdecadal Pacific Oscillation (IPO) is a mode of decadal to multidecadal climate variability in the Pacific Ocean, closely linked to the El Nino Southern Oscillation (ENSO). The IPO is associated with decadal changes in ENSO and its impacts. This includes influences on rainfall, streamflow, flood risk, surface temperature and agricultural production in Australia and around the world.  In our observed records, periods of accelerated global surface warming correspond with IPO positive phases, and hiatus periods correspond with IPO negative phases. There is emerging evidence that the hiatus in global surface temperatures since 1999-2001 is associated with the IPO. However, due to short observational records relative to the decadal timescale of the IPO and poor agreement between existing palaeoclimate reconstructions of the IPO, our understanding about the past and future evolution of the IPO and its impacts are uncertain. Dynamical theories for the IPO and its relationship to ENSO are multi-faceted and currently lack full scientific consensus. This seminar presents an update of recent work in understanding the IPO using observations, climate models and palaeoclimate data. This includes the presentation of a new index to track the IPO in models and observations and an evaluation of the IPO in CMIP5 climate models under pre-industrial conditions. A new high-resolution palaeoclimate reconstruction is presented, describing the variability of the IPO over the past 400 years. The reconstruction is based on the collation of over 200 multi-proxy palaeoclimate records from around the Pacific basin, including corals, tree rings, ice cores and cave sediments. In the presence of ever-increasing atmospheric greenhouse gas concentrations, there is an urgent need to better understand the IPO. The transition to the next IPO positive phase could bring an unprecedented acceleration in surface warming, with major implications for ecosystems and communities around the world.