Until now, scientists believed the WAIS was relatively small about 10 million years ago, before the Late Miocene.
The bulk, if not all, of the rising sea levels were also attributed to the bigger EAIS during periods of warming in the last 23 million years.
Lead author and PhD student Jim Marschalek, from the Department of Earth Science and Engineering at Imperial, said: “Our observations from the past help inform predictions of how the West Antarctic Ice Sheet, which is considered particularly vulnerable to rapid ice mass loss today, will respond under various future warming scenarios.”
With the threat of global warming shooting past 2C above pre-industrial levels, scientists around the globe are scrambling to figure out how the Antarctic will react to climate change.
The WAIS is considered particularly vulnerable to a warming atmosphere and ocean waters, both of which drive the melting of glaciers and surface ice.