Abstract
In 2002, W. H. Munk defined an important enigma of 20th century global mean sea-level (GMSL) rise that has yet to be resolved. First, he listed three canonical observations related to Earth rotation – (1) the slowing of the Earth’s rotation rate over the last three millennia inferred from ancient eclipse observations, and changes in (2) the amplitude and (3) orientation of the Earth’s rotation vector over the last century estimated from geodetic and astronomic measurements – and argued that they could all be fit by a model of ongoing glacial isostatic adjustment (GIA) associated with the last ice age. Second, he demonstrated that prevailing estimates of the 20th century rate of GMSL rise (~1.5-2.0 mm/yr), after correction for the maximum signal from ocean thermal expansion, implied mass flux from ice sheets and glaciers at a level that would grossly misfit the residual, GIA-corrected observations of Earth rotation. We demonstrate that the combination of lower estimates of 20th century GMSL rise (up to 1990), improved modeling of the GIA process, and a correction of eclipse records for a signal due to angular momentum exchange between the fluid outer core and mantle reconciles all three Earth rotation observations. This resolution adds confidence to recent estimates of the individual contributions to 20th century sea-level change and to projections of GMSL rise to the end of the 21st century based upon them.