While a vast body of scientific literature has demonstrated that people are causing long-term global warming, with this decade the hottest on record, a new study finds that 2023’s record-breaking temperatures were elevated even higher by another force: El Niño.

Global temperatures rose 0.3˚C from 2022 to 2023, making it the warmest year ever recorded, with heat climbing so quickly that experts struggled to explain it. But a team of climate scientists —including Princeton’s HMEI Director and Knox Taylor Professor of Geosciences Gabriel Vecchi, climate scientist Wenchang Yang and graduate student Sofia Menemenlis—has found that the 2023 outsize warming was primarily caused by El Niño Southern Oscillation (ENSO), a pattern of warm water temperatures in the Pacific Ocean that affect weather worldwide, causing a global temperature spike that surpassed the ongoing warming brought about by anthropogenic factors like the burning of fossil fuels. The findings were just published in the journal Atmospheric Chemistry and Physics and covered in Science.

“We underscore that our findings regarding the association of global warming spikes with ENSO do not undermine the vast body of literature on how anthropogenic activities are causing long-term global warming,” write the authors.