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Using satellite laser altimetry, basal melting of ice shelves is determined to be the main driver of Antarctic ice-sheet loss,with changing climate the likely cause. Ice shelves — those parts of the ice sheets that extend over the ocean — are known to provide a buttressing effect that limits the velocity of upstream glaciers and ice streams. In Antarctica, loss of ice shelves has already been implicated in the accelerated motion of some ice masses, but the extent of ice-shelf wasting remained unknown. Now, Pritchard et al. present a complete survey of Antarctic ice-shelf thinning between 2003 and 2008, and reveal loss rates of up to 7 metres per year. Much of the thinning is attributable to wind-driven movement of warm water through deep troughs crossing the continental shelf. The authors conclude that the thinning has led to loss of buttressing strength and accelerated loss of ice mass. Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying1,2 glacier acceleration along Antarctic ice-sheet coastal margins3. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves, potentially limiting their ability to buttress the flow of grounded tributary glaciers4. Indeed, recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula5. But the extent and magnitude of ice-shelf thickness change, the underlying causes of such change, and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted3. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary control of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow2. The highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen6 and Bellingshausen7 seas, and atmospheric warming on the Antarctic Peninsula8. This implies that climate forcing through changing winds influences Antarctic ice-sheet mass balance, and hence global sea level, on annual to decadal timescales.