Ice is lost through the calving of icebergs, and by melting year-round from the base of ice shelves.
Additionally in summer there is a little surface melting at warm sites. Two methods are used to determine whether the ice sheet is growing or shrinking. By measuring the difference between the accumulation of snow and the loss of ice, we can assess the change in the mass of the ice sheet. Unfortunately this method is prone to large uncertainties. Alternatively we can use a technique to measure directly whether the ice sheet is getting thicker or thinner.