El Niño in a changing climate: a multi-model study G. J. van Oldenborgh1, S. Y. Philip1, and M Collins2 1Royal Netherlands Meteorological Institute, P.O. Box 201, 3730 AE De Bilt, The Netherlands 2Hadley Centre for Climate Prediction and Research, Met Office, Exeter, UK
Abstract. In many parts of the world, climate projections for the next century
depend on potential changes in the properties of the El Niño - 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.
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.
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
Niño-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 Niño
and La Niña events. Based on this analysis of the multi-model ensemble, we
expect very little influence of global warming on ENSO.
Citation: van Oldenborgh, G. J., Philip, S. Y., and Collins, M: El Niño in a changing climate: a multi-model study, Ocean Sci., 1, 81-95, doi:10.5194/os-1-81-2005, 2005.