Marco Cattaneo
For many millennia, mankind has measured time based on the rotation of the Earth. A day lasts 24 hours, of 60 minutes each. And every minute lasts 60 seconds. But the devil, as we know, is in the details.
And the movement of the planet around its axis is not stable at all, on the geological time scale. Thus, with the advent of atomic clocks, since 1972 we have had to "adjust" the time by occasionally adding a split second to the Greenwich meridian time to keep it in line with the solar day.
The next leap second was expected in 2026. But according to an analysis published in Nature, the melting of ice sheets due to climate change is causing the Earth's rotation to slow down to such an extent that it is pushing it back by three years, in 2029. For the first time, moreover, it will be one second less, and not more.
The length of the day depends on several factors, such as the Moon's pull on the oceans or the currents in the planet's molten core. And satellite data show that since the 1990s our planet has become less spherical because the melting ice of Antarctica and Greenland has shifted its mass toward the equator. It is this flow of water away from the axis that slows its rotation.
Of course, a second… that will never be. In reality, in a world based on computer systems, for example for geographic location, inaccuracy in measuring time can cause serious problems.
For experts, the main concern is that it will have a negative effect, and existing codes do not take this into account, comments Elizabeth Donley, of the National Institute of Standards and Technology in Boulder, Colorado.
We have all the time to figure it out, but this tiny second is another sign of how quickly the planet is changing before our eyes.
