In a study published in the Journal of Geophysical Research: Solid Earth, researchers explain how the warming planet is slowing Earth’s rotation and lengthening the day at a rate not seen for the last 3.6 million years. The length of a day changes over time due to the gravitational effect of the moon, shifting tectonic plates and other geophysical processes on the planet’s surface and in the atmosphere.

Scientists in the study developed a methodology to model changes in the Earth’s rotation over millions of years that included the repeated growth and melting of continental ice sheets from the ice ages. Using their technique, they estimate that our day increased the equivalent of 1.33 milliseconds per century from just 2000 to 2020 due to the redistribution of water from melting polar ice sheets and glaciers.

The researchers expect the Earth’s rotation rate to continue to decline through the end of the century. While a millisecond is very short, they point out that precise space navigation relies upon accurate information about the Earth’s rotation.