Image Slideshow Arctic Institute of Denmark Danish National Survey and Cadastre Scott Polar Research Institute Natural History Museum of Denmark Natural History Museum of Denmark NASA Goddard Space Flight Center/US Geological Survey

Long-forgotten aerial photographs of Greenland from the 1930s, rediscovered in a castle outside Copenhagen, have allowed researchers to construct a history of glacier retreat and advance in the area. The work, by Anders Bjørk at the University of Copenhagen and his colleagues, aims to provide a deeper understanding of how climate change has affected ice loss and glacier movements over the past 80 years.

Most studies of Greenland's glaciers have been done only since imaging satellites became available in the 1970s, so the data are relatively short-term. But using photographs from 1930s aerial surveys of the southeast coast of Greenland, together with US military aerial shots from the Second World War and recent satellite images, Bjørk and his colleagues have been able to observe changes at high spatial resolution from a period in which few glacier measurements were previously available.

Analysis of the images reveals that over the past decade, glacier retreat was as vigorous as in a similar period of warming in the 1930s. However, whereas glaciers that spill into the ocean retreated rapidly in the 2000s, it was land-terminating glaciers that underwent the fastest regression 80 years ago.