Assessment of future ENSO changes in a CMIP3/CMIP5 multi‐model and multi‐index framework

Abstract

ABSTRACTAs main mode of interannual climate variability with worldwide teleconnections, El Niño‐Southern Oscillation (ENSO) holds high ecological, economical and social relevance. So far, studies on future ENSO changes draw a rather incoherent picture across climate models and ENSO indices. Here, we assess climate change signals and respective uncertainties in the frequency and variance of ENSO events using a comprehensive multidimensional approach: 10 different ENSO indices based on five climate variables and derived from four CMIP3 and nine CMIP5 models are investigated and compared systematically. Finally, one dimension of the problem (of various indices and various models as well as realizations) is removed by combining the 10 ENSO indices to a single ‘super’‐index, defined in the Empirical Orthogonal Function space.The most common signal across models and indices is found to be an increase of year‐to‐year variability of ENSO events until the end of our century, especially in the combined index. A significant strengthening in frequency occurs only in terms of La Niña events in some indices, whereas El Niño events appear to be barely sensitive to radiative forcing during the 21st century. This study highlights the importance of taking a more holistic multi‐model and multi‐index viewpoint when assessing future changes in ENSO behaviour and addressing higher‐moment characteristics of ENSO.