Scientists have observed a recent surge in shorter days on Earth, with July 9 being the shortest day of the year so far this summer. The International Earth Rotation and Reference Systems Service (IERS) reports that Earth spun faster by 1.34 milliseconds, clocking in at less than 24 hours for the past five years.
Astronomer Nicholas Stamatakos explains that variations in Earth’s rotation are caused by a mix of factors, including the moon’s gravitational pull. When the moon is close to the equator twice a month, it slows down Earth’s spin, while its proximity to the poles increases the planet’s speed. Additionally, the atmosphere and core work together to maintain angular momentum.
However, scientists still don’t fully understand why Earth’s core has been slowing down for 50 years, causing the solid Earth above to spin faster. “We don’t know what the core might do in the future,” says geophysicist Duncan Agnew.
While the short-term fluctuations have produced historically short days, Earth’s long-term trend is one of increasing day length over billions of years. The moon’s gravity has been slowing down Earth’s rotation since its formation, with analysis of ancient mollusk shells revealing that 70 million years ago, a day was only 23.5 hours long.
The recent surge in faster rotations may be due to climate change, which is changing Earth’s mass and slowing its spin. A study suggests that modern climate change has contributed to a lengthening of the day by about 0.6-0.7 milliseconds, with this rate expected to double in the coming century.
As scientists struggle to understand the complex interactions driving Earth’s rotation, accurate predictions beyond six months remain challenging due to the incomplete understanding of various geodetic phenomena.
Source: https://www.nationalgeographic.com/science/article/shortest-day-earth-rotation