Greenland Ice Sheet is More Vulnerable to Climate Change Due to Mushy Underside

It turns out that the Greenland Ice Sheet may be far more vulnerable to climate change than once thought. Scientists have created a new model that shows that despite its apparent stability, the ice sheet is more sensitive than earlier estimates suggested.

The Greenland Ice Sheet is the second-largest ice sheet in the world. It covers a staggering 1.7 million square kilometers, which is an area that's roughly eight times the size of the United Kingdom. It also contains enough ice to raise sea levels by more than seven meters if it were to melt completely.

Currently, the ice sheet is losing ice at a net annual rate of 200 gigatons. That's equivalent to about .6 millimeters of annual sea level rise. With other contributions, the seas are rising about three millimeters annually.

While other models of the Greenland Ice Sheet assume that the ice slides over hard and impermeable bedrock, this study incorporates new evidence from ground-based surveys that show soft and porous sediments can be found at the bottom of the ice sheet. More specifically, the new study identifies the intake and temporal storage of water by weak sediment beneath the ice sheet as a crucial process in governing the ice flow.

"When these large ice sheets melt, whether that's due to seasonal change or a warming climate, they don't melt like an ice cube," said Marion Bougamont, the lead researcher, in a news release. "Instead, there are two sources of net ice loss: melting on the surface and increased flow of the ice itself, and there is a connection between these two mechanisms which we don't fully understand and isn't taken into account by standard ice sheet models."

The scientists created a three-dimensional ice sheet model and used an observational record of surface melting. This allowed them to accurately reproduce how the ice sheet's seasonal movement changes in response to the amount of surface meltwater being delivered to the ground below. In the end, the scientists found that the ice sheet isn't nearly as resistant to melting as once thought.

"Not only is the ice sheet sensitive to a changing climate, but extreme meteorological events, such as heavy rainfall and heat waves, can also have a large effect on the rate of ice loss," said Poul Christoffersen, one of the researchers. "The soft sediment gets weaker as it tries to soak up more water, making it less resistant, so that the ice above moves faster. The Greenland Ice Sheet is not nearly as stable as we think."

The findings are published in the journal Nature Communications.