Program     Ocean-atmosphere interactions and multi-scale climate variability in a changing climate       0930 Increased variability of eastern Pacific El Niño under greenhouse warming  (Invited) Wednesday 9th @ 0930-0950, Concert Hall Wenju Cai* , Key Laboratory of Physical Oceanography, Institute for Advanced Ocean Studies, Ocean University of China and Qingdao National Laboratory for Marine Science and Technology, Qingdao, China/Centre for Southern Hemisphere Oceans Research (CSHOR), CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia Guojian Wang, Key Laboratory of Physical Oceanography, Institute for Advanced Ocean Studies, Ocean University of China and Qingdao National Laboratory for Marine Science and Technology, Qingdao, China/Centre for Southern Hemisphere Oceans Research (CSHOR), CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia Boris Dewitte, Centro de Estudios Avanzados en Zonas áridas, Coquimbo, Chile/Departamento de Biología, Facultad de Ciencias del Mar, Universidad Católica del Norte, Coquimbo, Chile/Millennium Nucleus for Ecology and Sustainable Management of Oceanic Islands, Coquimbo, Chile/Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, Toulouse, France Lixin Wu, Key Laboratory of Physical Oceanography, Institute for Advanced Ocean Studies, Ocean University of China and Qingdao National Laboratory for Marine Science and Technology, Qingdao, China Agus Santoso, Centre for Southern Hemisphere Oceans Research (CSHOR), CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia/Australian Research Council Centre of Excellence for Climate Extremes, The University of New South Wales, Sydney, New South Wales, Australia Ken Takahashi, Servicio Nacional de Meteorología e Hidrología del Perú—SENAMHI, Lima, Peru Yun Yang, College of Global Change and Earth System Science, Beijing Normal University and University Corporation for Polar Research, Beijing, China Aude Carréric, Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, Toulouse, France Michael J. McPhaden, NOAA/Pacific Marine Environmental Laboratory, Seattle, WA, USA Presenter Email: wenju.cai@csiro.au The El Niño–Southern Oscillation (ENSO) is the dominant and most consequential climate variation on Earth, and is characterized by warming of equatorial Pacific sea surface temperatures (SSTs) during the El Niño phase and cooling during the La Niña phase. ENSO events tend to have a centre—corresponding to the location of the maximum SST anomaly—in either the central equatorial Pacific (5° S–5° N, 160° E–150° W) or the eastern equatorial Pacific (5° S–5° N, 150°–90° W); these two distinct types of ENSO event are referred to as the CP-ENSO and EP-ENSO regimes, respectively. How the ENSO may change under future greenhouse warming is unknown, owing to a lack of inter-model agreement over the response of SSTs in the eastern equatorial Pacific to such warming. Here we find a robust increase in future EP-ENSO SST variability among CMIP5 climate models that simulate the two distinct ENSO regimes. We show that the EP-ENSO SST anomaly pattern and its centre differ greatly from one model to another, and therefore cannot be well represented by a single SST ‘index’ at the observed centre. However, although the locations of the anomaly centres differ in each model, we find a robust increase in SST variability at each anomaly centre across the majority of models considered. This increase in variability is largely due to greenhouse-warming-induced intensification of upper-ocean stratification in the equatorial Pacific, which enhances ocean–atmosphere coupling. An increase in SST variance implies an increase in the number of ‘strong’ EP-El Niño events (corresponding to large SST anomalies) and associated extreme weather events.

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