Posted by 
This story was originally published by the Guardian and is reproduced here as part of the Climate Desk collaboration.
The climate crisis is causing the length of each day to get longer, analysis shows, as the mass melting of polar ice reshapes the planet.
The phenomenon is a striking demonstration of how humanity’s actions are transforming the Earth, scientists said, rivalling natural processes that have existed for billions of years.
The change in the length of the day is on the scale of milliseconds but this is enough to potentially disrupt internet traffic, financial transactions, and GPS navigation, all of which rely on precise timekeeping.
The length of the Earth’s day has been steadily increasing over geological time due to the gravitational drag of the moon on the planet’s oceans and land. However, the melting of the Greenland and Antarctic ice sheets due to human-caused global heating has been redistributing water stored at high latitudes into the world’s oceans, leading to more water in the seas nearer the equator. This makes the Earth more oblate — or fatter — slowing the rotation of the planet and lengthening the day still further.
The planetary impact of humanity was also demonstrated recently by research that showed the redistribution of water had caused the Earth’s axis of rotation — the north and south poles — to move. Other work has revealed that humanity’s carbon emissions are shrinking the stratosphere.
“We can see our impact as humans on the whole Earth system, not just locally, like the rise in temperature, but really fundamentally, altering how it moves in space and rotates,” said professor Benedikt Soja of ETH Zurich in Switzerland, one of the world’s leading universities in science and technology. “Due to our carbon emissions, we have done this in just 100 or 200 years. Whereas the governing processes previously had been going on for billions of years, and that is striking.”
Human timekeeping is based on atomic clocks, which are extremely precise. However, the exact time of a day — one rotation of the Earth — varies due to lunar tides, climate impacts, and some other factors, such as the slow rebound of the Earth’s crust after the retreat of ice sheets formed in the last ice age.
These differences have to be accounted for, said Soja: “All the datacentres that run the internet, communications and financial transactions, they are based on precise timing. We also need a precise knowledge of time for navigation, and particularly for satellites and spacecraft.”
“Due to our carbon emissions, we have done this in just 100 or 200 years. Whereas the governing processes previously had been going on for billions of years, and that is striking.”
The research, published in the Proceedings of the National Academy of Sciences of the USA, used observations and computer reconstructions to assess the impact of melting ice on the length of the day. The rate of slowing varied between 0.3 and 1.0 millisecond per century between 1900 and 2000. But since 2000, as melting accelerated, the rate of change also accelerated to 1.3 millisecond per century.
“This present-day rate is likely higher than at any time in the past few thousand years,” the researchers said. “It is projected to remain approximately at a level of 1.0 millisecond per century for the next few decades, even if greenhouse gas emissions are severely curbed.” If emissions are not cut, the slowing rate will increase to 2.6 milliseconds per century by 2100, overtaking lunar tides as the single biggest contributor to long-term variations in the length of days, they said.
Dr. Santiago Belda of the University of Alicante in Spain, who was not part of the research team, said: “This study is a great advance because it confirms that the worrying loss of ice that Greenland and Antarctica are suffering has a direct impact on day length, causing our days to lengthen. This variation in day length has critical implications not only for how we measure time, but also for GPS and other technologies that govern our modern lives.”
