Understanding and modeling the ice sheets in a changing climate
Over the past three decades, observations have shown that both the Antarctic and Greenland Ice Sheets have been losing mass at an increasing rate. According to the Intergovernmental Panel on Climate Change (IPCC), glaciers and ice sheets have become today the largest contributors to sea level rise, but their contribution over the next century remains a key uncertainty in sea level rise projections. How the ice sheets interact with the other components of the Earth system and how they will respond to this negative mass balance have become some of the most urgent questions in understanding the implications of climate change. Understanding the past and future behavior of the ice sheets remains scientifically and technically challenging, and numerical modeling is the only effective tool to address this question. A new generation of ice sheet models that include a more complete physics of ice stream flow and improved forcing from the other components of the Earth System is emerging. This new generation of models is both improving our understanding of important physical processes, and reducing the uncertainty in the contribution of the ice sheets to sea level rise.
I will first illustrate how surface observations coupled with modeling tools can provide critical insights into important physical processes or ice properties that are difficult to observe directly (e.g., basal friction or ice thickness) for both the Greenland and Antarctic ice sheets. I will then show how climate forcings, and the ocean in particular, strongly affect ice sheet dynamics. Pine Island Glacier, for example, has been undergoing significant changes over the last few decades, and our simulations show that the largest climatic impact on ice dynamics is the rate of ice shelf melting, which rapidly affects glacier speed over several hundreds of kilometers upstream of the grounding line. I will finally present modeling results that include ice–ocean interactions beneath the ice shelves performed with coupled ice-sheet–ocean models. I will conclude with future research directions and new challenges.