Sediment cores were collected from a lake that captures runoff from two glaciers in Greenland. Our analysis of the sediments shows that these glaciers were active over the last 9,000 years and advanced and retreated in response to regional climate changes. The data also provide a long-term perspective on the rate of 20th century glacier retreat and indicate that recent anthropogenic-driven warming has already impacted the regional cryosphere in a manner outside the range of natural variability.