Tide gauge and satellite measurements indicate that global mean sea level has increased by 1.5 to 2.0 mm/year during the 20th century. A significant fraction of this increase is ascribed to glacial melting caused by warming, with the remainder due to thermal expansion of the oceans. Because glacial melting redistributes Earth's mass from high latitudes, where water is stored as ice, to lower latitudes, any appreciable melting should change the planet's rate of rotation, as when a spinning figure skater extends her arms, and the orientation of the rotational vector, which should move as mass shifts. However, the simultaneous agreement in the movement of the rotational pole, the historical observations of ancient eclipses (which allow trends in the length of day to be computed), and space-based gravity measurements (which reflect mass redistributions) has seemingly precluded any major amount of ice melting during the past hundred years.
Mitrovica et al. challenge that view with a new theory of rotational stability that involves reformulating how the shape of Earth has responded to glacial melting. In this way, they show how the full suite of Earth rotation and geodetic observations can be reconciled with those of glacial melting and associated sea level rise. -- HJS
Earth Planet. Sci. Lett. 243, 390 (2006).
