Ice sheet mass loss is adding to sea-level rise, and is expected to increase, but by how much and how fast remains uncertain. Isotopes produced in rock at the Earth’s surface provide records of past ice sheet thinning which help predict future change but are more effective if they are precise enough to determine past changes to the nearest thousand years. Carbon-14 is a unique isotope that provides an accurate record of past change since the last ice age, however, its precision can be improved.