Mass loss from the Greenland and Antarctic ice sheets is accelerating, and ice sheets are expected to be the dominant contributor to global sea level rise in the next several decades. Although advanced ice sheet models are now included in Earth system models, projections of future sea level rise remain very uncertain, with high-end estimates of more than 1 meter by 2100. NSF NCAR scientist William Lipscomb will discuss the challenges of simulating ice sheets and their interactions with the ocean and atmosphere using the Community Earth System Model. This talk will cover the basics of ice sheet modeling and the likelihood of abrupt sea level rise.