Anthropogenic polar melt and the lengthening day: Rotational slowdown, sea level redistribution, and navigation impacts

Abstract

Earth's rotation is not constant. Tidal friction has lengthened the day by about 1.8 ms per century over the years. Recent observations show an additional slowdown in rotation linked to human-caused climate change. Purpose: This review brings together the physical processes, observational evidence, and technological effects of climate-driven polar ice melt on Earth’s length of day (LOD), focusing on the years 2000 to 2020. We use satellite gravimetry (GRACE/GRACE-FO), altimetry (IMBIE), very long baseline interferometry (VLBI), GNSS, and paleoclimatic deep-learning analyses to quantify ice sheet mass loss, sea level change, and resulting LOD shifts. From 2000 to 2020, melting of the Greenland and Antarctic ice sheets moved mass toward the equator. This increased Earth’s moment of inertia and slowed its rotation by an extra 1.33 ± 0.08 ms per century. This climate-related effect now surpasses the natural slowdown caused by tidal friction and glacial isostatic adjustment. If this is not accounted for, the total timing error will reach 0.67 ms after 50 years, equivalent to a 200 km GNSS range error. This poses serious risks for autonomous vehicles, aviation, and maritime navigation. The expected first negative leap second has been delayed by three years; however, the accelerating ice melt may push it back indefinitely. Human-induced mass redistribution has become the primary cause of increased LOD, significantly affecting UTC leap-second policies and satellite positioning. We need urgent updates to Earth rotation models, a reassessment of the leap second system, and collaboration among glaciology, geodesy, and metrology to protect global navigation and timekeeping systems.