Recent mass balance of polar ice sheets inferred from patterns of global sea-level change

Global sea level is an indicator of climate change(1-3), as it is sensitive to both thermal expansion of the oceans and a reduction of land-based glac iers. Global sea-level rise has been estimated by correcting observations f rom tide gauges for glacial isostatic adjustment-the continuing sea-level r esponse due to melting of Late Pleistocene ice-and by computing the global mean of these residual trends(4-9). In such analyses, spatial patterns of s ealevel rise are assumed to be signals that will average out over geographi cally distributed tide-gauge data. But a long history of modelling studies( 10-12) has demonstrated that non-uniform- that is, non-eustatic-sea-level r edistributions can be produced by variations in the volume of the polar ice sheets. Here we present numerical predictions of gravitationally consisten t patterns of sea-level change following variations in either the Antarctic or Greenland ice sheets or the melting of a suite of small mountain glacie rs. These predictions are characterized by geometrically distinct patterns that reconcile spatial variations in previously published sea-level records . Under the-albeit coarse-assumption of a globally uniform thermal expansio n of the oceans, our approach suggests melting of the Greenland ice complex over the last century equivalent to similar to0.6 mm yr(-1) of sea-level r ise.