So Much Ice Has Melted, That the Earth’s Crust Is Shifting in Weird, New Ways

So Much Ice Has Melted, That the Earth’s Crust Is Shifting in Weird, New Ways

Both the Greenland and Antarctic ice sheets — the world’s two largest bodies of ice — are melting at an alarming rate, causing major problems for local ecosystems and coastal communities alike. Now, in yet more evidence that the climate crisis is changing everything in bizarre and profound ways, new research suggests that the meltdown is warping the Earth’s crust.

The new study, published in the journal Geophysical Research Letters last month, analyses satellite data of ice melt from 2003 to 2018. The authors paired this data with a model showing how changes in ice mass affect the crust. The model showed that much of the northern hemisphere moved horizontally because of melting ice in Greenland and the Arctic.

This happens because the planet’s outermost layer has a little more slack than you might think. When ice sheets build up, their weight causes the crust underpinning them to sink in order to compensate. When the ice melts, as it’s doing at a record rate due to rising temperatures, there’s less weight for the crust to bear so it rebounds.

“Think of a wooden board floating on top of a tub of water,” Sophie Coulson, planetary scientist at Harvard and lead author of the study, said in a press release. “When you push the board down, you would have the water beneath moving down. If you pick it up, you’ll see the water moving vertically to fill that space.” But like an old mattress or sofa cushion that maintains the depression of your body after you lie on it, the crust doesn’t always totally revert back to its old shape.

During the Ice Age, the Earth’s crust was weighed down by ice sheets that were thousands of feet thick. The Earth has bounced back in places where the ice sheets have since receded. But the new phenomenon is a whole different ballgame that’s being driven by climate change the rapid meltdown it’s causing.

Some previous studies have looked at the up-and-down motion that ice sheet melting can cause, but the new report took a closer look at horizontal shifts. In some places, the researchers found the horizontal shifts are more significant than the upward and downward ones. These changes are observable even in areas hundreds of miles away from the ice loss itself. Researchers teased them out using a variety of satellite data, including the network that helps provide GPS.

The movement is subtle, averaging far less than a millimetre a year globally. The crust under western Canada and the U.S. shifted horizontally by up to 0.3 millimetres per year. Elsewhere, the biggest shifts took place off the northern edge of Greenland, particularly during periods of major ice loss. West Antarctica and the Antarctic Peninsula, two hotspots for ice loss, also saw major (OK, “major”) movement as well, with the crust as far away as the Southern Ocean crawling back toward areas where the ice was disappearing.

These small shifts add up, and could actually lead to even more ice melt. Coulson said that the “rebounding of the crust is changing the slope of the bedrock under the ice sheet, and that can affect the ice dynamics.” In West Antarctic, for instance, the bedrock slopes downward further inland. The upward spring in the crust in the Southern Ocean could cause the slope to increase even further, sending more ocean water to undercut the ice. (To be clear, this is a nominal process and we have much bigger, direct climate change impacts on the ice sheet to worry about.)

The new study’s authors hope their research will help future studies and other researchers develop a new way to monitor the changes in the ice mass. Analysing this movement of the crust is crucial to predicting tectonic motions, earthquakes, and other geological processes.

“Understanding all of the factors that cause movement of the crust is really important for a wide range of Earth science problems,” said Coulson.

This is not the first time researchers have found that melting ice is causing major global changes. Previous studies have found that disappearing ice has redistributed enough water to shift Earth’s axis by moving its rotational poles. The new study is the latest reminder that the climate crisis is driving wide-ranging major changes to the very structure of the Earth — and unless the world phases out the use of fossil fuels, those profound shifts will continue.

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