American Alpine Club library’s archive of images by early mountaineers holds clues for researchers documenting the retreat of glaciers worldwide.

Early in the Alpine Club’s history, climbers were interested in photos of glaciers so they could see what obstacles faced them before they traveled to attempt a mountain. They used some of the earliest film cameras to document the valleys filled with ice. In 2019, scientists have a more pressing interest, and new equipment to match.

Ted Scambos, a senior research scientist at the Cooperative Institute for Research in Environmental Sciences, a University of Colorado and NOAA partnership, estimates the Arapaho Glacier has lost 75 percent of its ice in the last 100 years. To get an idea of the glacier’s range at the turn of the century, he turned to old photographs.