Why has Earth's axis tilted by 31.5 inches and what does it mean?

Planet Earth (Nasa/American Institute of Biology/PA) (PA Media)
Planet Earth (Nasa/American Institute of Biology/PA) (PA Media)

Humans may have significantly shifted the Earth’s rotation by 80 centimetres to the east due to large quantities of water being pumped out of the ground.

Findings published in Geophysical Research Letters revealed that between 1993 and 2010 alone, water extraction led an estimated 2,150 billion tonnes to be sucked up from beneath the Earth’s surface.

Northwestern India and western North America showed significant decreases in groundwater storage.

The water has mostly been used for drinking, irrigation, and agriculture as the rapidly growing world population and climate change sent demand rising.

According to the UN, climate change is exacerbating both water scarcity and water-related hazards. Over the past twenty years, terrestrial water storage – including soil moisture, snow and ice – has dropped at a rate of 1cm per year, with major ramifications for water security.

How has water pumping made the Earth’s axis tilt?

Water eventually finds its way back into the oceans as it evaporates from land, before returning to the Earth as rainfall and running off into rivers and the sea.

As a result, there has been a massive relocation of water on the planet and distribution to oceans.

Earth has therefore tilted it on its axis at a rate of about 1.7 inches (4.3 centimetres) a year, giving a total of 78.5 centimetres, during the 18-year study period.

While spinning on its axis, Earth wobbles like an off-kilter top (about 20 to 60 inches every six to 14 years). The distribution of water on the planet affects how mass is distributed.

A study by Nature showed higher sea levels have slowed down Earth’s rotation because they change the concentration of the plant’s mass, making it spin less quickly than it used to.

However, a lot of factors can affect the speed of our planet’s rotation, including ocean tides and the disappearance of ice caps.

What does this mean for the planet?

Groundwater depletion is a significant contributor to a rise in the global mean sea level estimate (GMSL), experts have said. Data about time-variable gravity has shown a connection between large amounts of groundwater depletion and sea level rise.

The redistribution of water pushed up the global sea level by 0.24 inches in the 18 years to 2010.

Despite the slight rise, scientists say the rate of water distribution has accelerated significantly in recent decades and expect the trend to continue, as climate change and rising populations push demand for water ever higher.

The connection between sea levels and the Earth’s rotation

According to the scientist behind the Nature study, the connection between sea levels and the Earth’s rotation can be likened to a figure skater.

"If you have a skater who starts spinning, if she lowers her arms or stretches out her legs, she will slow down,” said Duncan Agnew, author of the study and a geophysicist at the Scripps Institution of Oceanography at the University of California.

When skaters pull their arms in, they spin faster – the opposite of what’s happening to our planet because of climate change.

“It’s kind of impressive, even to me, we’ve done something that measurably changes how fast the Earth rotates,” Agnew added. “Things are happening that are unprecedented.”