How we worked out that climate change messes with Earth’s spin
Cosmic radio waves and computer models revealed the phenomenon
A cosmic radio broadcast helped tell us what was going on. The tilt of our planet was changing.
Out there in space, extremely bright centres of galaxies called quasars send blasts of radio waves across the cosmos. And those signals are really useful. Carefully monitoring the arrival of those radio waves on Earth is one method scientists use to monitor variations in our planet’s spin.
How? Say you have two antennae at different locations on Earth listening to radio waves from a quasar – you’ll be able to detect a time difference between when those signals arrive. If the discrepancy between those arrivals changes over time, then you know the Earth’s orientation, such as its tilt, must also be changing. A bit like a bat using echolocation to orient itself.
Our planet is forever in motion. Spinning on its axis, orbiting the sun. But humans are throwing that motion out of whack. As the world gets hotter due to climate change, causing droughts and irregular rainfall, more and more people have been pumping water out of the ground. It’s causing some problems.
We are taking so much water out of the ground that rainfall is no longer able to replenish it in many parts of the world – and giant sinkholes (caused in part by groundwater extraction) large enough to swallow entire buildings, are becoming more common.
Combined with the runoff from melting icebergs and glaciers, groundwater redistributed to the oceans is exacerbating sea-level rise. An excess of water is forming around the equator – meaning Earth’s very shape is changing. It’s getting flatter (and fatter), basically. This massive shift is affecting how the planet spins, altering Earth’s tilt to the tune of 4.36 centimetres per year.
In 2023, geophysicists published an analysis of this phenomenon. They used computer models to show that this 4.36 centimetre shift was dependent on humans having redistributed 2,150 gigatons of groundwater.
Sea change
More and more pumping of groundwater is expected to occur in the coming years – largely in response to climate change. A 2012 paper estimated that groundwater redistribution would cause sea-levels to rise by 0.82 millimetres per year by 2050 (The Intergovernmental Panel on Climate Change notes that sea-level rise is already at 3-4 millimetres per year and could rise to somewhere between 4 and 20 millimetres per year by 2100).
Earth becoming flatter also means that the length of days – the time it takes for the planet to spin around on its axis once – is changing. A full spin, or Earth day is getting longer by around 1.33 milliseconds every 100 years. This is more than the variation in day length (between 0.3 and 1 millisecond per 100 years) that was observed during the 20th Century.
Researchers who quantified the shift in a 2024 study used satellite observations of water and ice redistribution on Earth to help them make their estimate.
Just think about that. Emissions from human activities, and human pumping of groundwater, is significant enough to alter the very motion of our planet.
Sometimes, the impact is especially dramatic.
In 2023, a glacier in Greenland melted enough to collapse a mountain peak, which in turn caused a huge landslide and a tsunami. The sloshing of water back and forth in a narrow fjord was strong enough to send seismic waves reverberating across the planet – it made the Earth vibrate for nine days.
This, too, is an example of climate change feedback. When you think about it, the phrase “climate change” arguably does not capture, or even hint at, the truly seismic shifts our planet is experiencing because of human activity.
Earth is literally shaking.
Further reading on this week’s story
Nasa has published an in-depth article explaining how scientists study the relationship between climate change and Earth’s motion.
In June, BBC News reported on how cities around the world are “sinking” due to excessive groundwater pumping.
Sea-level rise and extreme storms are powerful enough to have a small but noticeably effect on the frequency of earthquakes, according to a 2024 study.
Thanks for reading! If you enjoyed this story, don’t forget to share it with your friends and colleagues. You can also subscribe to The Reengineer and follow me on Bluesky.
Now add to this that Australia exports approximately 898 million tonnes of iron ore annually (!), from the southern hemisphere to industrial centers in the northern hemisphere (China, Korea, etc). There is no way that such an enormous amount of iron shift over now years doesn’t / hasn’t also affected the earth magnetic fields and pole locations!?