Ice sheet melt tied to shift in geographic pole motion

Nature : Earth’s geographic poles have long been known to shift seasonally in a generally circular direction because of changes in snow, rain, and humidity. There is also a yearly motion that is believed to be partly driven by continental drift. Between 1982 and 2005, the North Pole shifted roughly 2 milliarcseconds (mas) per year in a southeasterly direction. In 2005 the pole’s motion changed significantly; it started moving directly eastward (toward Greenland) at a rate of 7 mas/year. Jianli Chen of the University of Texas at Austin and his colleagues used data from NASA’s Gravity Recovery and Climate Experiment ( GRACE) satellite to compare changes in Earth’s gravitational distribution and estimates of ice sheet loss in Greenland. They found that 90% of the pole’s shift in direction and speed was due to the increased loss of ice and associated sea-level rise. Chen suggests that measurements of polar motion taken over the past century could be used to check the estimates of ice loss over that same period.