In 2023, the world experienced its highest ever global mean surface temperature (GMST). Our study underscores the pivotal significance of El Niño and sea surface temperature (SST) warming as the fundamental causes. Interannually, the increment of GMST in 2023 comprised two phases: first, gradual ocean warming associated with El Niño and the North Atlantic from January to August; second, a continued rise in land temperatures in the mid‐to‐high latitude regions from September onwards, influenced by SST patterns. Notably, the maturation of El Niño prolonged warming in North America through excitation of the Pacific‐North American teleconnection. During the most recent 15 years, GMST has entered an accelerated warming period, primarily driven by rapid SST warming trends in the tropical Indian Ocean, tropical Atlantic, subtropical North Pacific, and North Atlantic. These decadal warming patterns, combined with El Niño, may further increase GMST, with 2023 as a particularly striking example.