Very early warning of a moderate-to-strong El Ni\~no in 2023

The El Ni\~no Southern Oscillation (ENSO) is the strongest driver of year-to-year variations of the global climate and can lead to extreme weather conditions and disasters in various regions around the world. Here, we review two different approaches for the early forecast of El Ni\~no that we have developed recently: the climate network-based approach allows forecasting the onset of an El Ni\~no event about 1 year ahead, while the complexity-based approach allows additionally to estimate the magnitude of an upcoming El Ni\~no event in the calendar year before. For 2023, both approaches predict the onset of an El Ni\~no event, with a combined onset probability of about 89%. The complexity-based approach predicts a moderate-to-strong El Ni\~no with a magnitude of $1.49\pm0.37${\deg}C. Since El Ni\~no events temporarily increase the global temperature, we expect that the coming El Ni\~no will increase the global temperature by about +0.2{\deg}C, likely making 2024 the hottest year since the beginning of instrumental observations. It is possible that as a consequence of this El Ni\~no, the +1.5{\deg}C target (compared to pre-industrial levels) will be temporarily breached already in 2024.