Aerial photographs of Greenland from the 1930s — rediscovered in a castle outside Copenhagen — could provide a deeper understanding of the impact of climate change on the island's glaciers than the use of satellite data alone.

Most studies of Greenland's glaciers have used satellite imagery collected since the 1960s. Anders Bjørk at the University of Copenhagen and his colleagues found the historical images of 132 Greenlandic glaciers (pictured) and compared them with more recent satellite data. The comparison shows that, overall, glacier retreat over the past decade has been as vigorous as in a similar period of warming in the 1930s. However, glaciers with edges that reach the ocean tended to retreat more rapidly in the 2000s than in the 1930s, whereas those terminating on land regressed faster 80 years ago than in the 2000s.

Nature Geosci. http://dx.doi.org/10.1038/ngeo1481 (2012)