Climate change has altered the Earth’s tilt
Earth’s poles are moving – that’s normal – but new research suggests that within just decades, climate change and human water use have given them an additional nudge. Any object’s spin is affected by how its weight is distributed. Earth’s weight distribution is always changing as the planet’s molten innards roil and its surface morphs.
Water is a key influencer, since it’s so heavy. In the past two decades, two super-sensitive NASA satellite missions – the Gravity Recovery and Climate Experiment (GRACE) and its successor GRACE-FO – have analysed this shifting weight, but those observations only began in 2002.
In the new research, scientists focused on shifts in Earth’s tilt in the 1990s, before that satellite data existed. Instead the researchers turned to observations of the water itself – measurements of ice loss and statistics on groundwater pumped out for human use – to combine with studies of how the poles drifted.
In 1995 polar drift changed direction completely, and between that year and 2020, the speed of the pole movement increased about 17 times compared to the average speed measured between 1981 and 1995. By combining the polar drift data with the water data, the researchers showed that most of the pole movement was triggered by water loss from polar regions – ice melting off land and flowing into the oceans – with smaller input from water loss in other regions, where humans pull groundwater up to use.