The Greenland ice sheet is far more vulnerable to climate change than wraps previously thought, based on recent findings from the University of Cambridge.
Through the use of a new model — which takes into account the role that the “soft, spongy ground beneath the ice sheet plays in its changing dynamics”, as well as meltwater impacts — researchers at the university determined the increased instability.
Given the massive size of the ice sheet (1.7 million square kilometers), and the world changing effects that its melting would have, the findings are worth noting. If/when the ice sheet melts completely, global sea levels will rise by an average of seven meters.
“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,” stated Dr Marion Bougamont of Cambridge’s Scott Polar Research Institute, who led the research. “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 University of Cambridge provides more:
Whereas other models of the Greenland Ice Sheet typically assume the ice slides over hard and impermeable bedrock – an assumption which is largely practical and based on lack of constraints – this study incorporates new evidence from ground-based surveys, which show soft and porous sediments at the bed of the ice sheet, more like the soft and muddy bottom of a lake than a sheet of solid rock. The new study specifically identifies the intake and temporal storage of water by weak sediment beneath the ice sheet as a crucial process in governing the ice flow.
Using a three-dimensional ice sheet model, together with an observational record of surface melting produced by collaborators at Aberystwyth University, Dr Bougamont and Dr Poul Christoffersen were able 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.
Lakes which form on the surfaces of glaciers, known as supraglacial lakes, are often created during the melt season, and typically last from early June to late August. Co-author Professor Alun Hubbard of Aberystwyth University studied these lakes and found that many empty in just a matter of hours, when hydrofracturing opens up water-filled crevasses, resulting in huge amounts of water entering and flooding the subglacial environment. In warmer years, these high-discharge drainage events are expected to become even more frequent.
“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,” explained Dr Christoffersen. “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.”
Current (very conservative predictions) argue that complete collapse of the ice sheet is unlikely within this century, but will probably come sometime soon after that. I’d like to posit though, that such predictions reflect greatly on the notoriously conservative nature of most of the predictions put out there by the scientific community. A collapse sometime towards the end of the century is most certainly a real possibility.
The new findings are detailed in a paper just published in the journal Nature Communications.
Image Credit: Sam Doyle