The melting of ice in Greenland and Antarctica modifies the speed of the Earth’s rotation faster than expected and that will alter the calculation of universal time on which computer networks adjust, says a study published recently.
Since 1967, Universal Coordinated Time (UCT) has been established with ultra-sensitive atomic clocks that keep time around the world and ensure the accuracy of digital and communication infrastructures such as satellite navigation.
For historical reasons, synchrony was maintained between the UCT and astronomical time, calculated from the Earth’s rotation speed, which is not constant. Starting in 1972, it was decided to compensate for the irregularities by adding leap seconds to atomic time, so that it coincides with astronomical time.
These leap seconds are added every time the lag between both measurements approaches 0.9 seconds. The last time this adjustment was made was in 2016, Duncan Agnew, author of one of the studies on the subject, published by the journal Nature, explained.
But changing the speed of the Earth’s rotation poses an inverse problem, since it will cause astronomical time to advance ahead of atomic time. And that would force, within a few years, to introduce a negative leap second.
A real worry
Such a novelty worries metrology specialists, who measure time, since the introduction of a negative leap second would pose “unprecedented” problems in “an increasingly connected world,” says PatriziaTavella, from the International Bureau of Weights and Measures.(BIPM), in a commentary attached to the study.
The uncertainty comes from the fact that computer programs that integrate leap seconds “assume that leap seconds are always positive,” adds Duncan Agnew of the Institute of Geophysics at the University of California, San Diego.
The Earth slows down
Partly because of this new situation, metrologists around the world agreed to stop introducing leap seconds until 2035.And starting that year, it is planned to let the difference between atomic time and the Earth’s rotation reach one minute.
But according to Nature, that program could be compromised by global warming, due to the acceleration of melting in Greenland and Antarctica, which Agnew measured with satellite observations.
Since the 1990s, the melting of ice has slowed down the rotation of the Earth, just as the tides caused by the gravitational force that the Moon and the Sun exert on our planet do, counterbalancing the natural acceleration.“When the ice melts, water spreads throughout the ocean (…), which modifies the distribution of fluids on the surface and inside the Earth,” details the scientist.
All this in itself is not new, because the slowing effect caused by melting was suggested at the end of the 19th century and has been measured since the 1950s, says Duncan Agnew.“But the novelty of my work is to show the extent of the impact of melting on the Earth’s rotation. A change never seen before,” he highlights.
The slowdown is such that it could delay an eventual transition to the negative second until 2029, according to forecasts. Without the impacts of global warming, this would probably occur as early as 2026.
This postponement gives a break to metrologists, who will have “more time to decide if 2035 is the best date to eliminate the leap second or if it should be abandoned earlier,” comments PatriziaTavella, from the BIPM.
