Human-driven melting slows Earth’s spin at an unprecedented pace

A new study shows Earth's day length is increasing at about 1.33 milliseconds per century—unprecedented in 3.6 million years—driven by mass shifting from melting polar ice into the oceans. The redistribution (around 1000 gigatonnes) slows rotation to a level whose energy is comparable to a magnitude 9.0 earthquake; if high-emission trends continue, climate change could become the leading driver of day-length change by century’s end, with subtle effects on GPS and spacecraft navigation. Researchers note today’s human activity is matching a rare natural event from ~2 million years ago and plan to study other mass-shift processes like groundwater depletion.