Humans have affected the Earth’s rotation, scientists say

Humans may have altered the Earth’s rotation significantly between 1993 and 2010 alone by pumping large quantities of water out of the ground and moving it elsewhere.

Alarming levels of groundwater extraction have tilted the Earth nearly 80cm (31.5 inches) east during this period, found research published in the journal Geophysical Research Letters.

Previous studies have shown that the position of the Earth’s axis – or its rotational pole – changes relative to the crust, with the planet spinning a little differently as water is moved around.

Scientists have estimated using climate models that humans pumped 2,150 gigatons of groundwater – equivalent to over 6mm (0.24 inches) of sea level rise from 1993-2010.

While water’s ability to change the Earth’s rotation was first discovered in 2016, the specific contribution of groundwater to these rotational changes has remained elusive.

The new study modelled the observed changes in the drift of the planet’s rotational pole and the movement of water.

It first assessed the impact of only ice sheets and glaciers and then considered different scenarios of groundwater redistribution.

“Earth’s rotational pole actually changes a lot. Our study shows that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole,” said study co-author Ki-Weon Seo, a geophysicist at Seoul National University in South Korea.

The model was found to be off by 78.5cm (31 inches) or 4.3cm (1.7 inches) of drift per year when considering 2,150 gigatons of groundwater redistribution.

“I’m very glad to find the unexplained cause of the rotation pole drift. On the other hand, as a resident of Earth and a father, I’m concerned and surprised to see that pumping groundwater is another source of sea-level rise,” Dr Seo said.

The findings suggest the location from which the groundwater is drawn matters for how much it could change polar drift.

For instance, scientists said redistributing water from the mid-latitudes has a larger impact on the rotational pole.

Researchers said the most water was redistributed in western North America and northwestern India, both at mid-latitudes during the period from 1993 to 2010.

Attempts by countries to slow groundwater depletion rates, especially in these sensitive regions, can theoretically alter the change in drift, scientists said.

However, this could work only if such conservation approaches are sustained for decades.

Since the Earth’s rotational pole normally changes by several meters within about a year, changes due to groundwater pumping don’t pose any risk of shifting seasons, researchers said.

But the axis drift has been shown to have an impact on climate over long, geological time scales.

In further research, scientists hope to understand water storage variations during the last 100 years and whether global heating had any impact on this.