On secular geocenter motion: The impact of climate changes

We investigate the impact of recent climate changes on the long-term displacement of the Center of Figure (CF) of the Earth (also defined as the geocenter in our convention) with respect to the Center of Mass of the whole Earth (CM). The two realizations of the International Terrestrial Reference System (ITRS), entitled ITRF2000 and ITRF2005, present a difference of 1.8 mm/yr between the velocities of their respective frame origins, suggesting an acceleration of the geocenter towards the North Pole. We investigate if such a displacement could be explained by geophysical phenomena, such as the present ice melting and the sea level rise. Using published observations on ice caps and glaciers, we calculated the range of geocenter motion that may occur today. We found that the global ice melting induces long-term displacements of the geocenter mainly along the Z-axis, toward the North Pole. The geocenter velocity is today between 0.3 and 0.7–0.8 mm/yr and has doubled during last decade with the recent acceleration of ice melting. Combining with Greff-Lefftz (2000) results on post-glacial rebound, we conclude that a present secular geocenter velocity of 1 mm/yr is possible. However, the recent increase of the geocenter velocity cannot explain the difference observed between the two last realizations of the ITRS. Our results comfort the previous conclusions about ITRF2000 and ITRF2005 and the pre-analysis of ITRF2008 data, suggesting that the large Z-translation rate between the ITRS realizations is probably due to an imprecise ITRF2000 origin. Finally, we show that determining precisely the geocenter velocity would give a new type of information that may be useful to more precisely constrain mass exchanges associated with climate changes.