Melting ice slows down the Earth's rotation. And it affects the measurement of time


By John

The climate change has intertwined its destiny with that of the measurement of terrestrial time. Events such as lo melting of polar ice in remote locations such as Greenland and Antarctica are influencing the angular speed of our planet, or the rate of its rotation around its axis. This alteration has significant repercussions on the adaptation of the Coordinated Universal Time (UTC), which serves as a global reference for defining all world time zones. Since it became necessary to implement periodic corrections to the UTC in 1972, there has been much discussion about the possible introduction of a “negative leap second”, i.e. a decrease in time, initially scheduled for 2026 but now postponed to 2029.

Change of geophysical perspective

The research conducted by Duncan Carr Agnew from the University of California at San Diego and published in Nature highlights how the melting of ice modifies the distribution of Earth's mass, thus altering the shape of the planet from a sphere to a geoid. Second Massimo Frezzottiglaciologist and professor at Roma Tre University, over the last forty years the melting of ice at the poles has increased six times, marginally but significantly influencing the rotation speed of the Earth.

The challenges of temporal precision

UTC is calibrated through data from approximately 450 atomic clocks dispersed across more than 80 laboratories worldwide. These clocks, which measure time through the vibrations of cesium atoms, have extreme precision. However, precision clashes with irregularities in the Earth's rotation, caused for example by tides, which make the rotation speed variable. Since 1972, the leap second figure was introduced to synchronize UTC with atomic time, requiring the addition of 27 leap seconds whenever the discrepancy between the two measurement methods approached 0.6 seconds.

Future prospects

The need to remove a “leap second” represents an absolute novelty that could generate unprecedented complications in satellite navigation systems, computers and financial markets, all dependent on UTC. Agnew's mathematical simulations of changes in the Earth's angular momentum indicate that the slowing of the Earth's rotation, accelerated by melting ice, will postpone the need for the negative leap second by 2029.

Massimo Frezzotti concludes by observing that climate change, by affecting the weather, highlights already marked effects that are destined to intensify in the future.