Earth’s geographic poles aren’t fixed. Instead, they wander in seasonal and near-annual cycles. The weather and ocean currents drive most of this slow drift. But a sudden zag in the direction of that drift started in the 1990s. That sharp change in direction appears due in large part to the melting of glaciers, a new study finds. And that melt? Climate change triggered it.
The geographic poles are where the planet’s axis pierces Earth’s surface. Those poles move in relatively tight swirls just a few meters across. They also drift over time as the distribution of the planet’s weight shifts. That shift in mass alters the rotation of Earth about its axis.
Before the mid-1990s, the North Pole had been drifting toward the western edge of Canada’s Ellesmere Island. It’s part of Canada’s Nunavut territory, just off Greenland’s northwest shoulder. But then the pole veered eastward by about 71 degrees. That sent it toward the northeastern tip of Greenland. It has continued to head that way, moving about 10 centimeters (4 inches) per year. Scientists aren’t quite sure why this shift occurred, says Suxia Liu. She’s a hydrologist at the Institute of Geographic Sciences and Natural Resources Research. It’s in Beijing, China.
Liu’s team checked how well the trends in the changing polar drift match data from studies on melting across the globe. In particular, glacial melt sped up during the 1990s in Alaska, Greenland and the southern Andes. The timing of that accelerated melting helped link it to Earth’s changing climate. This, as well as the effects that the melt would have had on altering the distribution of Earth’s mass, suggests glacial melting helped trigger the change in polar drift. Liu and her colleagues described their findings April 16 in Geophysical Research Letters.
While melting glaciers can account for much of the change in polar drift, it doesn’t explain all of it. This means other factors must also be at work. Farmers, for instance, have been pumping lots of groundwater from aquifers for irrigation. Once brought to the surface, that water can drain to rivers. Eventually, it can flow to an ocean far away. Like glacial melt, how water is managed cannot alone explain the North Pole’s drift, the team reports. It can, however, give Earth’s axis a substantial nudge.
The findings “reveal how much human activity can have an impact on changes to the mass of water stored on land,” says Vincent Humphrey. He’s a climate scientist at the University of Zurich in Switzerland. The new data also show how large these shifts in our planet’s mass can be, he adds. “They’re so big that they can change the axis of the Earth.”