Multi-year La Niñas Break the Interannual Symmetric GMST Responses to Strong ENSO Events

Strong El Niño and La Niña events typically produce symmetric impacts on global mean surface temperature (GMST), inducing notable warming or cooling, respectively, from their developing year through the boreal summer of the following year. However, this symmetry in GMST response breaks down in the subsequent autumn and winter, and the underlying mechanism has remained unclear. This study reveals that the opposite transition behaviors of strong ENSOs are key to this breakdown: while strong El Niños commonly transition into La Niña, strong La Niñas more often persist into multi-year episodes, resulting in asymmetric climate trajectories. These divergent evolutions produce asymmetric GMST anomalies since post-summer, including not only the divergent locations and intensities of cold sea surface temperature over tropical Pacific, but also the contrasting land surface temperature dipoles over the Northern Hemisphere’s mid-to-high latitudes, mediated by tropical–extratropical teleconnections. These findings highlight a previously underappreciated source of GMST variability and offer new insight into its predictability on interannual–biennial timescales.