| El Niño - Southern Oscillation (ENSO) influences the weather in large parts of the world. Climate projections for these regions therefore depend on the predictions of the properties of ENSO in a warming world. The predictions of current climate models are very uncertain, as different models show very different trends in mean state and variability of ENSO. We will reduce the uncertainty in the predictions by considering the ENSO theory that describes it as a mix of two modes: a subsurface mode in the eastern Pacific and a surface mode in the central Pacific. A balance in the model between these modes close to the observed mix is a prerequisite for a reliable ENSO prediction. We will determine the properties of these modes in a set of climate models including the Hadley Centre and KNMI models and compare these with observations. Next the evolution of the two modes and their interaction under global warming will be studied. The model formulations closest to reality, chosen from a large ensemble of experiments with the Hadley Centre model with perturbed parametrizations, and tuned in the KNMI model, will give a prediction with smaller uncertainties of ENSO properties in the next 100 years. Finally we will investigate decadal variability in these models, again using the two-mode description of ENSO, and compare this with the observations of temperature and pressure in the equatorial Pacific over the last 130 years. |
