Recent change in ENSO’s impacts on the summertime circumglobal teleconnection and mid-latitude extremes

The boreal summer circumglobal teleconnection (CGT) provides valuable predictability sources for mid-latitude Northern Hemisphere climate anomalies and extreme events. Here, we show that the CGT’s circulation structure has displaced westward by a half-wavelength since the late 1970s, more severely impacting heatwaves and droughts over East Europe, East Asia and southwestern America. We present convergent empirical and modelling evidence to reveal the essential role of El Niño-Southern Oscillation (ENSO) in shaping this change. Before the late 1970s, ENSO indirectly promoted CGT by modulating the Indian summer monsoon rainfall (ISMR). Recently, the ENSO–ISMR linkage was weakened, but the westward-displaced ENSO forcing was able to directly trigger a Rossby wave response at the exit of the East Asian westerly jet due to the easterly vertical shear of the zonal basic flow over the tropical western North Pacific, thus shifting the previous CGT’s North Pacific and downstream centers westward along the subtropical jet waveguide. Moreover, the state-of-the-art models with prescribed anthropogenic forcing cannot simulate such changes, indicating their origin from natural variability. The knowledge gained from this work highlights the importance of studying the impacts of changing ENSO to improve seasonal prediction of mid-latitude extreme events.