At the current rate of retreat the vast glaciers, which extend deep into the heart of the ice sheet, could contribute as much as 3.4 metres to global sea level rise over the next several centuries.
Antarctica is covered by two huge ice masses: the East and West Antarctic Ice Sheets, which feed many individual glaciers. Because of the warming climate, the WAIS has been thinning at accelerated rates over the past few decades. Within the ice sheet, the Thwaites and Pine Island glaciers are particularly vulnerable to global warming and are already contributing to rises in sea level.
Now, a new study led by the University of Maine and the British Antarctic Survey, including academics from Imperial College London, has measured the rate of local sea level change – an indirect way to measure ice loss – around these particularly vulnerable glaciers.
They found that the glaciers have begun retreating at a rate not seen in the last 5,500 years. With areas of 192,000 km2 (nearly the size of the island of Great Britain) and 162,300 km2 respectively, the Thwaites and Pine Island glaciers have the potential to cause large rises in global sea level.
“These currently elevated rates of ice melting may signal that those vital arteries from the heart of the West Antarctic Ice Sheet have been ruptured, leading to accelerating flow into the ocean that is potentially disastrous for future global sea level in a warming world. Is it too late to stop the bleeding?”
During the mid-Holocene period, over 5,000 years ago, the climate was warmer than today and thus sea levels were higher and glaciers smaller. The researchers wanted to study fluctuations in sea level since the mid-Holocene, so studied the remnants of old Antarctic beaches, which are today elevated above modern sea level.
They examined seashells and penguin bones on these beaches using radiocarbon dating – a technique that uses the radioactive decay of carbon locked in the shells and bones as a clock to tell us how long they have sat above sea level.
When heavy glaciers sit on the land, they push down or ‘load’ the Earth’s surface. After the glaciers’ ice melts or ‘unloads’, the land ‘bounces back’ so that what once was a beach is now higher than sea level. This explains why the local sea level for this land fell, while globally the water from the melting ice caused global sea levels to rise.
By pinpointing the precise age of these beaches, they could tell when each beach appeared and therefore reconstruct changes in local, or ‘relative’, sea level over time.
The results showed a steady fall in relative sea level over the last 5,500 years, which the researchers interpret as a result of ice loss just prior to that time. This pattern is consistent with relatively stable glacier behaviour with no evidence of large-scale glacier loss or advance.
The paper is published in Nature Geoscience.