El Niño phenomenon may slightly lengthen Earth's day

Strong El Niño events can slow Earth's rotation, potentially lengthening a day by approximately one millisecond. According to the National Oceanic and Atmospheric Administration (NOAA), this phenomenon is caused by large-scale redistribution of mass within the atmosphere and oceans.

During El Niño, trade winds in the tropical Pacific weaken while winds in other regions strengthen. This shift alters the distribution of angular momentum between the Earth and its atmosphere. Scientists compare this effect to a figure skater: when arms are extended away from the body, rotation slows down. Conversely, the La Niña phase tends to have the opposite effect, potentially speeding up rotation and shortening the day.

While these changes are imperceptible to humans, they are measurable and significant for scientists requiring high precision for satellite positioning, astronomical observations, and timekeeping. Other factors also influence Earth's rotation, such as melting glaciers, which redistribute mass from land to oceans and contribute to long-term slowing of the planet's rotation.