Climate change effects on Earth's spin

 Earth is wobbling and days are getting longer, NASA-funded study shows        

New studies, which utilized AI to monitor the effects of climate change on Earth's spin, have shown that our days are getting increasingly longer and that our planet will get more wobbly in the future. These changes could have major implications for humanity's future. Earth's days are getting longer as the planet's spin slows down, and the melting of ice by human-caused climate change is partly to blame, say researchers. A NASA-funded study used over 120 years of data to show how melting glaciers and ice sheets, dwindling groundwater and rising seas are affecting Earth's spin axis and lengthening its days. Since the year 2000, the study says, days have been getting longer by 1.33 milliseconds per 100 years, marking the fastest such change compared to any time in the previous century.

Melting ice affects

Earth's days are getting longer, and the extent of this change is accelerating. Plus, the planet's rotational axis moved about 30 feet (10 metres) in the past 120 years. This, say researchers, is a result of a redistribution of ice and water caused as ice sheets and glaciers melt more than they accumulate from snowfall. It's also caused by loss of groundwater that's not being replenished by rain. The effect of these phenomena is a shift in mass which causes Earth to wobble and its spin axis to move (known as 'polar motion'). Earth moves much faster than it seems. The length of Earth's days and the orientation of our planet are being thrown out of balance as human-caused climate change continuously alters Earth's spin, new research suggests. Initially, these changes will be imperceptible to us, but they could have serious knock-on effects, including forcing us to introduce negative leap seconds, interfering with space travel and altering our planet's inner core, researchers warn. A day on Earth lasts about 86,400 seconds. But the exact time it takes our planet to complete a single rotation can shift by tiny fractions of milliseconds every year due to a number of factors, such as tectonic plate movements, changes to the inner core's rotation and gravitational tugging from the moon.

A paper published in Nature Geoscience entitled Contributions of core, mantle and climatological processes to Earth’s polar motion states that these mass variations during the 20th century were mostly a result of natural climate cycles. "The common thread between the two papers is that climate-related changes on Earth’s surface, whether human-caused or not, are strong drivers of the changes we’re seeing in the planet’s rotation," says Surendra Adhikari, a co-author of both papers and a geophysicist at NASA’s Jet Propulsion Laboratory in Southern California. Studies of the 120-year-old data found that 90% of fluctuations between 1900 and 2018 are a result of changes in groundwater, ice sheets, glaciers, and sea level, with the remainder caused by changes in Earth's interior. The changes caused by a shift in surface mass occurred frequently throughout the 20th century: a few times every 25 years. This suggests the changes were largely a result of natural climate change. However, more recent papers have looked at changes caused by human activities.

Human-caused climate change is another factor that can alter the length of our days, and scientists are just starting to realize how much this will affect our planet's spin in the coming years. Over the past few decades, the rate of ice loss from Earth's polar regions, particularly Greenland and Antarctica, has been increasing rapidly due to global warming, leading to rising sea levels. Most of this extra water accumulates near the equator, causing our planet to bulge slightly around the middle. This, in turn, slows the planet's spin because more weight is distributed farther away from the planet's centre, similar to how spinning figure skaters slow down by moving their arms away from their bodies. In the new study, published on 15 July in the journal PNAS, researchers used an advanced artificial intelligence program that combines real-world data with the laws of physics to predict how the planet's spin will change over time.

One paper authored by Adhikari shows how an eastward drift of Earth's axis that began around 2000 could be caused by melting of Greenland and Antarctic ice sheets and groundwater depletion in Eurasia. Faster melting of ice sheets is shifting mass from Earth's poles to the equator, causing the planet's spin to slow and the days to get longer. Global warming has triggered sea level rises, which are impacting Earth's rotation. The results back up a similar study published in March, which suggested that Earth's days will get longer in the future. However, the new program offered much more precise estimates of how days will lengthen over time. The same research team behind the new paper also released another study, published on 12 July in the journal Nature Geoscience, which showed that the increased water near the equator is moving Earth's axis of rotation. This is making the magnetic poles wobble farther away from the axis every year.

Scientists previously found that this effect has likely been happening for at least the past three decades. However, the new study suggests the axis will move even farther from its current position than previous studies predicted. "We humans have a greater impact on our planet than we realise," Benedikt Soja, a geodesist at ETH Zurich in Switzerland who was a co-author on both the studies, said. "And this naturally places great responsibility on us for the future of our planet." Earth's days have always varied in length. Around 1 billion years ago, our planet likely took only 19 hours to complete a single rotation, before slowing to the 24 hours we experience today. It also changes on shorter timescales. For example, in 2020, Earth was spinning more quickly than at any point since records began in 1960. In 2021, the planet's rotation began to slow down again even though we experienced the shortest-ever recorded day in June 2022.

But in general, Earth's rotation has been slowing for millennia, mainly due to a process known as lunar tidal friction, in which the moon's gravitational effect on our oceans pulls water away from the poles. At the moment, this effect is lengthening our days by around 2.3 milliseconds every century. The new studies show that climate change is currently lengthening our days by around 1.3 milliseconds every century. However, based on current global temperature models, the researchers predict that this could increase to 2.6 milliseconds per century by the end of the 21st century, which would make climate change the biggest influence on our planet's spin.

 

 

Potential impacts

Any changes to Earth's spin will have to be accounted for during space travel, researchers say. One of the most likely effects of longer days would be the need to introduce negative leap seconds, where we'd occasionally lose a second from some future days to accommodate the lengthening days, similar to how leap years work. The study suggests that this may need to start happening as soon as 2029, mainly to accommodate for how much the days have already lengthened over the past few millennia. In the past, scientists have suggested this introduction could mess with the timekeeping of computers and smartphones. However, not everyone is convinced this will be a major issue. The researchers of the new studies also noted that future changes could impact space travel. "Even if the Earth's rotation is changing only slowly, this effect has to be taken into account when navigating in space, for example, when sending a space probe to land on another planet," Soja said. It is therefore important to monitor these changes closely, he added. The team also warned that the changes to Earth's rotational axis could alter the rotation of Earth's inner core, which could further increase how fast days lengthen. However, this potential interaction is still largely unknown.

Conclusion

From 2000 to 2018, the rate of increase of the length of a day on Earth caused by the movement of ice and groundwater was 1.33 milliseconds per century. That's faster than any period in the previous century. Researchers say that action to severely reduce emissions by 2100 could decelerate the lengthening of Earth's days caused by ice and groundwater changes. But if emissions continue to rise, say researchers, the lengthening of Earth's day caused by climate change could be as much as 2.62 milliseconds per century. "In barely 100 years, human beings have altered the climate system to such a degree that we’re seeing the impact on the very way the planet spins," says Adhikari.