
Earth is spinning faster, making days shorter — here's why scientists say it could be a problem
July 10 was the shortest day of the year so far, lasting 1.36 milliseconds less than 24 hours, according to data from the International Earth Rotation and Reference Systems Service and the US Naval Observatory, compiled by timeanddate.com. More exceptionally short days are coming on July 22 and August 5, currently predicted to be 1.34 and 1.25 milliseconds shorter than 24 hours, respectively.
The length of a day is the time it takes for the planet to complete one full rotation on its axis —24 hours or 86,400 seconds on average. But in reality, each rotation is slightly irregular due to a variety of factors, such as the gravitational pull of the moon, seasonal changes in the atmosphere and the influence of Earth's liquid core. As a result, a full rotation usually takes slightly less or slightly more than 86,400 seconds — a discrepancy of just milliseconds that doesn't have any obvious effect on everyday life.
However these discrepancies can, in the long run, affect computers, satellites and telecommunications, which is why even the smallest time deviations are tracked using atomic clocks, which were introduced in 1955. Some experts believe this could lead to a scenario similar to the Y2K problem, which threatened to bring modern civilization to a halt.
Atomic clocks count the oscillations of atoms held in a vacuum chamber within the clock itself to calculate 24 hours to the utmost degree of precision. We call the resulting time UTC, or Coordinated Universal Time, which is based on around 450 atomic clocks and is the global standard for timekeeping, as well as the time to which all our phones and computers are set.
Astronomers also keep track of Earth's rotation — using satellites that check the position of the planet relative to fixed stars, for example — and can detect minute differences between the atomic clocks' time and the amount of time it actually takes Earth to complete a full rotation. Last year, on July 5, 2024, Earth experienced the shortest day ever recorded since the advent of the atomic clock 65 years ago, at 1.66 milliseconds less than 24 hours.
'We've been on a trend toward slightly faster days since 1972,' said Duncan Agnew, a professor emeritus of geophysics at the Scripps Institution of Oceanography and a research geophysicist at the University of California, San Diego. 'But there are fluctuations. It's like watching the stock market, really. There are long-term trends, and then there are peaks and falls.'
In 1972, after decades of rotating relatively slowly, Earth's spin had accumulated such a delay relative to atomic time that the International Earth Rotation and Reference Systems Service mandated the addition of a 'leap second' to the UTC. This is similar to the leap year, which adds an extra day to February every four years to account for the discrepancy between the Gregorian calendar and the time it takes Earth to complete one orbit around the sun.
Since 1972, a total of 27 leap seconds have been added to the UTC, but the rate of addition has increasingly slowed, due to Earth speeding up; nine leap seconds were added throughout the 1970s while no new leap seconds have been added since 2016.
In 2022, the General Conference on Weights and Measures (CGPM) voted to retire the leap second by 2035, meaning we may never see another one added to the clocks. But if Earth keeps spinning faster for several more years, according to Agnew, eventually one second might need to be removed from the UTC. 'There's never been a negative leap second,' he said, 'but the probability of having one between now and 2035 is about 40%.'
The shortest-term changes in Earth's rotation, Agnew said, come from the moon and the tides, which make it spin slower when the satellite is over the equator and faster when it's at higher or lower altitudes. This effect compounds with the fact that during the summer Earth naturally spins faster — the result of the atmosphere itself slowing down due to seasonal changes, such as the jet stream moving north or south; the laws of physics dictate that the overall angular momentum of Earth and its atmosphere must remain constant, so the rotation speed lost by the atmosphere is picked up by the planet itself. Similarly, for the past 50 years Earth's liquid core has also been slowing down, with the solid Earth around it speeding up.
By looking at the combination of these effects, scientists can predict if an upcoming day could be particularly short. 'These fluctuations have short-period correlations, which means that if Earth is speeding up on one day, it tends to be speeding up the next day, too,' said Judah Levine, a physicist and a fellow of the National Institute of Standards and Technology in the time and frequency division. 'But that correlation disappears as you go to longer and longer intervals. And when you get to a year, the prediction becomes quite uncertain. In fact, the International Earth Rotation and Reference Systems Service doesn't predict further in advance than a year.'
While one short day doesn't make any difference, Levine said, the recent trend of shorter days is increasing the possibility of a negative leap second. 'When the leap second system was defined in 1972, nobody ever really thought that the negative second would ever happen,' he noted. 'It was just something that was put into the standard because you had to do it for completeness. Everybody assumed that only positive leap seconds would ever be needed, but now the shortening of the days makes (negative leap seconds) in danger of happening, so to speak.'
The prospect of a negative leap second raises concerns because there are still ongoing problems with positive leap seconds after 50 years, explained Levine. 'There are still places that do it wrong or do it at the wrong time, or do it (with) the wrong number, and so on. And that's with a positive leap second, which has been done over and over. There's a much greater concern about the negative leap second, because it's never been tested, never been tried.'
Because so many fundamental technologies systems rely on clocks and time to function, such as telecommunications, financial transactions, electric grids and GPS satellites just to name a few, the advent of the negative leap second is, according to Levine, somewhat akin to the Y2K problem — the moment at the turn of the last century when the world thought a kind of doomsday would ensue because computers might have been unable to negotiate the new date format, going from '99' to '00.'
Climate change is also a contributing factor to the issue of the leap second, but in a surprising way. While global warming has had considerable negative impacts on Earth, when it comes to our timekeeping, it has served to counteract the forces that are speeding up Earth's spin. A study published last year by Agnew in the journal Nature details how ice melting in Antarctica and Greenland is spreading over the oceans, slowing down Earth's rotation — much like a skater spinning with their arms over their head, but spinning slower if the arms are tucked along the body.
'If that ice had not melted, if we had not had global warming, then we would already be having a leap negative leap second, or we would be very close to having it,' Agnew said. Meltwater from Greenland and Antarctica ice sheets has is responsible for a third of the global sea level rise since 1993, according to NASA.
The mass shift of this melting ice is not only causing changes in Earth's rotation speed, but also in its rotation axis, according to research led by Benedikt Soja, an assistant professor at the department of civil, environmental and geomatic engineering of The Swiss Federal Institute of Technology in Zurich, Switzerland. If warming continues, its effect might become dominant. 'By the end of this century, in a pessimistic scenario (in which humans continue to emit more greenhouse gases) the effect of climate change could surpass the effect of the moon, which has been really driving Earth's rotation for the past few billions of years,' Soja said.
At the moment, potentially having more time to prepare for action is helpful, given the uncertainty of long-term predictions on Earth's spinning behavior. 'I think the (faster spinning) is still within reasonable boundaries, so it could be natural variability,' Soja said. 'Maybe in a few years, we could see again a different situation, and long term, we could see the planet slowing down again. That would be my intuition, but you never know.'
Hashtags

Try Our AI Features
Explore what Daily8 AI can do for you:
Comments
No comments yet...
Related Articles
Yahoo
3 hours ago
- Yahoo
US bans vaccine ingredient targeted by anti-vaxxers
The US health department said Wednesday it would end the use of a vaccine ingredient long targeted by conspiracy theorists over debunked claims it causes autism. Thimerosal, a preservative that prevents bacterial and fungal contamination in multidose vials, has been extensively studied, with authorities including the World Health Organization finding no evidence of harm. The move follows a vote by a panel of outside experts convened by Kennedy last month that voted to end the use of thimerosal in influenza vaccines for adults, pregnant people and children. Although the substance is now rarely used in US vaccines, the recommendations by the influential Advisory Committee on Immunization Practices alarmed experts, who said the move has effectively embedded talking points championed by the anti-vaccine movement into national policy. ia/sms


New York Post
3 hours ago
- New York Post
Ex-DOGE lawyer launches AI policy council to push US to front of tech race with China
WASHINGTON — A former top lawyer at the Department of Government Efficiency launched a new artificial intelligence policy council on Wednesday, coinciding with executive actions by President Trump to deregulating the industry, The Post can reveal. James Burnham, who also held a senior position in the Department of Justice during Trump's first term, is founding the AI Innovation Council to push an 'America First' approach to AI and prevent China from winning the race for global tech dominance — both economically and militarily. 'Artificial intelligence is a revolutionary technology with the potential to make the United States wealthier and greater than it has ever been,' he said. Advertisement 3 The Department of Government Efficiency's former top lawyer James Burnham is launching a new artificial intelligence policy council on Wednesday to coincide with executive actions by the Trump administration. LinkedIn / James Burnham 'That's why President Trump made clear in his first week back in office that 'the policy of the United States is to sustain and enhance America's global AI dominance in order to promote human flourishing, economic competitiveness, and national security.' 'I have been as outspoken as anyone about the problems of Big Tech and monopoly power, but it's a major mistake to let legitimate concerns about past abuses block new innovators from propelling our nation into a new golden age.' Advertisement The new council will sketch out regulatory frameworks for AI and help boost US-based companies. 3 The 'AI Action Plan' will be touted by the president's czar on the issue, Silicon Valley billionaire David Sacks, and will further promote the 'export' of American AI tech abroad and build out data centers in the US. AP Trump, 79, is set to sign several AI-related executive orders Wednesday afternoon — including an expected action to curb 'woke' models. The 'AI Action Plan' will be touted by the president's AI czar, Silicon Valley billionaire David Sacks, and will further promote the 'export' of American tech abroad and build out data centers in the US. Advertisement Last week, Sacks joined Trump in announcing more than $100 billion in AI- and energy-related private sector investments at a forum in Pittsburgh. 3 Last week, Sacks joined Trump in announcing more than $100 billion in AI- and energy-related private sector investments at a forum in Pittsburgh. Getty Images The administration may also prevent states from taking too heavy a hand in regulating the industry, according to a summary seen by Reuters. Advertisement A proposed moratorium on state and local AI regulation was removed from the One Big Beautiful Bill Act by congressional Republicans before Trump signed it July 4. 'The goal isn't just to win the innovation race,' Burnham said. 'It's to help launch America's golden age.'


New York Times
3 hours ago
- New York Times
There's Fungus Among Us. But Where Exactly?
The world's biological riches are not evenly distributed. Instead, much of Earth's plant and animal life is concentrated in a small number of biodiversity hot spots — from the tropical rainforests of the Amazon to the alpine meadows of the Himalayas — that have earned enormous scientific and conservation attention. Now, new research suggests that more of these critical hot spots could be hiding beneath our feet — undocumented and largely unprotected. On Wednesday, an international team of scientists unveiled a global underground atlas, mapping the biodiversity of organisms known as mycorrhizal fungi. The fungi, which live in and on plant roots, form vast underground networks and perform critical ecosystem services, transporting nutrients to plants, storing carbon, bolstering soil health and helping crops survive environmental shocks and stresses. Using machine learning models, the scientists predicted that rich reservoirs of these fungi lie hidden in some unexpected places, including the Alaskan tundra and Mediterranean woodlands and scrublands. The dense Amazonian jungle did not stand out as a fungal biodiversity hot spot, but the neighboring savanna, the Brazilian Cerrado, did. 'The Amazon of the underground is not actually in the Amazon rainforest,' said Michael Van Nuland, the lead data scientist at the Society for the Protection of Underground Networks, a research organization that led the mapping effort. 'These patterns of diversity that we're seeing are unique.' Alarmingly, they found, relatively few of these critical hot spots are in ecologically protected areas. Want all of The Times? Subscribe.