The El Niño Southern Oscillation is the dominant climate mode in the tropics but remains unpredictable due to strong variations in the heating zones of the tropical Pacific ocean among different El Niño events. Based on a theoretical approach, two researchers from CECI/CERFACS have shown that this diversity can be explained by the zonal (i.e. longitudinal) displacements of the background circulation of the Pacific or so-called Walker circulation. The work has been carried out within the framework of the ANR ARISE project and results have just been published in the journal Nature Geosciences (https://www.nature.com/articles/s41561-023-01154-x; see also: https://www.insu.cnrs.fr/fr/cnrsinfo/la-variabilite-del-nino-expliquee-par-les-deplacements-zonaux-de-la-circulation-de-walker). The results open new avenues to better understand the biases of current climate models as well as the evolution of the El Niño Southern Oscillation with climate change.