OS Ocean Science OS Ocean Sci. 1812-0792 Copernicus Publications Göttingen, Germany 10.5194/os-1-81-2005 El Niño in a changing climate: a multi-model study van Oldenborgh G. J. 1 Philip S. Y. 1 Collins M 2 Royal Netherlands Meteorological Institute, P.O. Box 201, 3730 AE De Bilt, The Netherlands Hadley Centre for Climate Prediction and Research, Met Office, Exeter, UK 13 10 2005 1 2 81 95 Copyright: © 2005 G. J. van Oldenborgh et al. 2005 This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 Generic License. To view a copy of this licence, visit https://creativecommons.org/licenses/by-nc-sa/2.5/ This article is available from https://os.copernicus.org/articles/1/81/2005/os-1-81-2005.html The full text article is available as a PDF file from https://os.copernicus.org/articles/1/81/2005/os-1-81-2005.pdf

In many parts of the world, climate projections for the next century depend on potential changes in the properties of the El Ni&#241;o - Southern Oscillation (ENSO). The current staus of these projections is assessed by examining a large set of climate model experiments prepared for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Firstly, the patterns and time series of present-day ENSO-like model variability in the tropical Pacific Ocean are compared with that observed. Next, the strength of the coupled atmosphere-ocean feedback loops responsible for generating the ENSO cycle in the models are evaluated. Finally, we consider the projections of the models with, what we consider to be, the most realistic ENSO variability. <br /><br /> Two of the models considered do not have interannual variability in the tropical Pacific Ocean. Three models show a very regular ENSO cycle due to a strong local wind feedback in the central Pacific and weak sea surface temperature (SST) damping. Six other models have a higher frequency ENSO cycle than observed due to a weak east Pacific upwelling feedback loop. One model has much stronger upwelling feedback than observed, and another one cannot be described simply by the analysis technique. The remaining six models have a reasonable balance of feedback mechanisms and in four of these the interannual mode also resembles the observed ENSO both spatially and temporally. <br /><br /> Over the period 2051-2100 (under various scenarios) the most realistic six models show either no change in the mean state or a slight shift towards El Ni&#241;o-like conditions with an amplitude at most a quarter of the present day interannual standard deviation. We see no statistically significant changes in amplitude of ENSO variability in the future, with changes in the standard deviation of a Southern Oscillation Index that are no larger than observed decadal variations. Uncertainties in the skewness of the variability are too large to make any statements about the future relative strength of El Ni&#241;o and La Ni&#241;a events. Based on this analysis of the multi-model ensemble, we expect very little influence of global warming on ENSO.