The rapid increase in global warming in 2023 has sparked fears that Earth has entered a new warm state. Possible explanations for a warming spike have included transient changes in radiative forcing or deficiencies in climate models. This study shows that the primary cause is a mode of natural climate variability – the El Niño/Southern Oscillation (ENSO). The authors show that, while the magnitude of global warming caused by ENSO was particularly large in 2023, it is not unprecedented in the historical record. The implication is that global warming is continuing at a steady average rate without dramatic acceleration.