Timing El Ni~no: analytical results

The El Niño Southern Oscillation (ENSO) is the leading mode of interannual variability in the global climatesystem. A complex collection of geophysical causes contributes to it, and many efforts have been made to reduceits representation to a simple model that describes its mean features and the fluctuations. Up to now the resultshave mainly been on the stationary statistical properties but here, for the first time, we obtain an analytical resultfor the timing of El Niño events. We arrive to that introducing in this field an approach derived from the context ofthe foundation of Thermodynamics: the role of the "microscopic" system is played by the atmosphere, while the ElNiño ocean variables play the role of the "macroscopic" system. Thus, as for Thermodynamics, El Niño emergesas a universal large scale property from a general class of complex systems.