The consequences of man-made climate change were overwhelmingly recognized by the world last December, when the landmark Paris agreement was signed by 195 nations. Chief among these dangers was sea level rise, which is already engulfing low-lying countries. A timely new study in Nature Communications reveals that the melting of the West Antarctic Ice Sheet (WAIS) could contribute 3.3 meters (10.8 feet) to sea level rise.

The WAIS is an icy behemoth, 25.4 million cubic kilometers (6.1 million cubic miles) in size. Unfortunately, it is fundamentally unstable. The Thwaites Glacier, which is often referred to as the “weak underbelly” of the WAIS, has melted and retreated to a remarkable extent over the last 20 years. This has left the WAIS particularly vulnerable to increasingly warm seawater, which is slowly eroding away the ice sheet’s base.

Although the WAIS is currently held in place by an underwater ledge, it’s not looking good: The melting rate for the WAIS has tripled in the last 10 years alone. With this in mind, a research team led by the University of Edinburgh decided to investigate the long-term stability of the ice sheet.

When glaciers and ice sheets move, shrink, or grow they leave traces on the underlying rocky landscape, moving huge boulders across the continent and depositing them far from their point of origin. This also causes the slope angles of the bedrock’s peaks and valleys to change over time.

If the underlying bedrock is brought to or left behind on the surface of the ice, it is bombarded by cosmic rays which produce rare, unstable isotopes, or forms of elements. By looking at the isotopic chemistry of these rocks, the length of time that they had been exposed to the atmosphere can be determined.

^{A researcher looks at some of the exposed rocks on the WAIS. Andy Hein/University of Edinburgh}

By examining the slope angles and the geochemistry of the peaks of the Ellsworth Mountains – the highest mountain range in Antarctica that was once covered in far more of the WAIS – the researchers were able to determine how the WAIS has either grown or shrunk over time.

The results indicate that during previous warmer periods, known as interglacials, a substantial amount of the WAIS would have melted, but it wouldn’t have completely disappeared. In fact, at least some of the WAIS has existed continuously for the last 1.4 million years.

The Quaternary Period, which began 2.4 million years ago and is still ongoing, has seen glacial-interglacial cycles – ice growth and shrinkage – occur roughly every 100,000 years. This is due to the wobble of the Earth on its rotational axis, which causes global temperature changes. This study indicates that, during even the warmest interglacials, the WAIS has managed to survive.

This, unfortunately, doesn’t mean that humanity is safe from sea level rise. During the interglacial period we are currently in, which is uncharacteristically warm thanks to man-made greenhouse gas emissions, the melting of the WAIS will still cause 3.3 meters (10.8 feet) of sea rise, even if it doesn’t completely disappear.

Dr. Andrew Hein, a researcher at the University of Edinburgh and lead author of the study, said in a statement that “this remains a troubling forecast, since all signs suggest the ice from West Antarctica could disappear relatively quickly.”