Global warming is shaking up the calculation of universal time

The melting of ice due to global warming is modifying the speed of rotation of the Earth more quickly than expected, to the point of affecting the calculation of universal time which determines the proper functioning of computer networks, according to a study on Wednesday.

Since 1967, Coordinated Universal Time (UTC) has been calculated using measurements from ultra-stable atomic clocks, which provide time around the world and enable digital and communications infrastructure, such as satellite navigation, to function. extremely precisely.

For historical reasons, UTC time remains linked to astronomical time, calculated with the Earth’s rotation speed, which is not constant. It was therefore decided, in 1972, to add a leap second to atomic time to make it coincide with astronomical time.

This addition occurs, irregularly, each time the difference between the two standards approaches 0.9 seconds. The last addition dates back to 2016, Duncan Agnew, author of a study published in Nature, told AFP.

But the acceleration of the Earth’s rotation means that astronomical time will gradually exceed atomic time. Which could force us to introduce, within a few years, a second… negative.

A leap into the unknown feared by metrologists, scientists who measure time, given the “unprecedented” problems that this could cause “in an increasingly connected world”, underlines Patrizia Tavella, of the International Weights Bureau and measurements (BIPM), in a commentary attached to the study.

“I would not recommend being on a plane at that time,” says Demetrios Matsakis, former chief scientist at the United States Naval Observatory, who did not take part in the work.

Because computer programs that integrate leap seconds “assume that they are all positive,” explains Duncan Agnew, of the Institute of Geophysics at the University of California at San Diego.

The Earth slows down

This is partly why metrologists around the world have agreed to eliminate the leap second by 2035.

From that year onwards, it was planned to allow the difference between atomic time and the rotation of the Earth to increase to one minute. But what to do in the meantime?

According to the study of Nature, global warming could disrupt the program. In question: the acceleration of the melting of the ice in Greenland and Antarctica, which the researcher was able to measure thanks to satellite observations.

Since the 1990s, melting ice has slowed the Earth’s rotation, as do the tidal effects of the Moon and Sun, counteracting the natural acceleration. “When the ice melts, water spreads across the entire ocean. (…) Which modifies the distribution of fluids on the surface and inside the Earth,” explains the scientist.

So far nothing new – the slowing effect of melting ice was suggested at the end of the 19th century, and it has been calculated since the 1950s, notes Duncan Agnew. “But the novelty of my work is to show the extent of the impact of melting ice on the rotation of the Earth. A change never seen before,” he says.

The slowdown is such that it could postpone a possible transition to the negative second until 2029, according to its forecasts. Without the effects of global warming, it would undoubtedly have had to be added in 2026.

This delay is rather welcome for metrologists, giving them “more time to decide whether 2035 is the best date to eliminate the leap second, or whether it should be abandoned before then,” reacted Patrizia Tavella, from the BIPM.


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