The change is invisible to humans but forces us to recalibrate our clocks more frequently.
The day isn’t precisely 24 hours to the millisecond, not even close. The duration of our planet’s rotation isn’t even stable; it has gradually lengthened at the rate of milliseconds per century, increasing by a few hours over millions of years. The main culprit has been the gravitational interaction with a receding moon.
But now, something else is altering the Earth’s rotation.
New factor. A new study published in the journal Proceedings of the National Academy of Sciences (PNAS) suggests that climate change may be responsible for accelerating the rate at which days are getting longer. In other words, the speed of the Earth’s rotation is slowing at an increasing rate.
Changes in distribution. What does one have to do with the other? The connection between climate change and the length of the day isn't intuitive, even though we know that melting the great ice sheets at the poles mediates this relation.
As the ice melts, large masses of water, previously concentrated at the poles, move to lower latitudes. This mass redistribution affects the planet’s angular momentum, which must be constant, so the rate of rotation changes.
Just as an ice skater can change the speed at which they rotate by changing the distribution of their mass—the ice skater will rotate faster if they concentrate their weight near the axis of rotation and slower if, for example, they stretch out one leg—the Earth will rotate more slowly as the mass of water moves away from the poles and toward the equator.
A matter of milliseconds. The team behind the study combined observations with reconstructions of landmass changes since 1900. They estimated that during the 20th century, the length of the day increased at a rate of 0.3 to 1 millisecond per century. However, so far in the 21st century, this rate of change has increased to 1.33 milliseconds, with a margin of error of ±0.03 milliseconds.
According to the study results, the effect of climate change might be worse to the extent that it could surpass the lunar retreat as the leading cause of the increase in the length of days. Also, the results indicate that this increase could reach 2.62 milliseconds per century by 2100 (with a margin of error of ±0.79 milliseconds).
Tangible impact. A change of this magnitude is invisible to humans, but it isn’t for our infrastructures in the digital era. Today, systems such as GPS need to keep a tight grip on time, so much so that they even have to consider relativistic changes due to the speed at which they orbit.
Such changes could be relevant in systems that require this kind of millisecond precision. In practice, we rely on leap seconds to set our clocks today. Leap seconds work like leap years, except we add seconds instead of days. The greater the speed loss, the more frequent these leap seconds must be.
To do this, the team used physically informed neural networks. These artificial intelligence-based tools can apply the laws of physics to generate automated learning algorithms, the researchers state in their study published in PNAS.
Changes in the Earth’s axis. The team behind the study of the effects of climate change on the Earth’s rotation complemented their investigation with another work published in the journal Nature Geoscience on other changes in these dynamics.
According to the second study, the Earth’s rotation axis is changing slightly due to alterations in the distribution of land masses, not only at the surface but also internally. This means the geographic poles could change like the magnetic ones, but at slower rates: tens of meters per century.
This article was written by Pablo Martínez-Juarez and originally published in Spanish on Xataka.
Image | NASA
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