The global environment has changed beyond recognition over the past century, presenting unprecedented challenges in environmental resource management, including biodiversity loss, deforestation and climate change. To address these challenges, we need to understand the causes and consequences of long-run environmental change. To understand long-run environmental change, we must be able to measure it. Satellite imagery allows us to measure environmental change in recent decades, but researchers have to date been unable to analyze long-run large-scale environmental change further back in time. In partnership with the Bodleian Library in Oxford and the National Collection of Aerial Photography in Edinburgh, we will digitize, process and make accessible a remarkable archive of 1.6 million aerial photographs from across the developing world, dating back to the late 1930s. In doing so, we will expand the horizon over which data are available to study global long-run environmental change by between 30 and 60 years, or more than 50%. Access to the archive has so far been extremely limited. We will transform the archive into a digitized, merged dataset, accessible online, which will allow researchers to look back in time to the beginning of WWII and the decolonization era. We expect the data to be applicable in fields as diverse as geology, archaeology, ecology, and climatology. In particular, we will use these data to study the relationships between development and the environment.