Warm ocean currents are melting many of Antarctica’s floating ice shelves from beneath, which in turn is speeding up the flow of land-based glaciers into the ocean and increasing global sea levels, according to a new study. An international team of scientists, led by researchers from the British Antarctic Survey (BAS), used 4.5 million measurements from a satellite-based laser altimeter that precisely measures the changing thickness of ice shelves. Using those readings and other data, the researchers determined that 20 of 54 ice shelves that flow off the Antarctic continent and float on the Southern Ocean are melting and thinning from below. Most of the 20 ice shelves are in West Antarctica, where air and ocean temperatures have been steadily rising in recent years. Along the western Antarctic Peninsula, eight ice shelves have fully or partially collapsed in the past several decades, allowing inland glaciers to surge into the sea. But the study, published in Nature, found that even the thinning of ice shelves, without total collapse, speeds up the flow of inland glaciers, increasing global sea levels.