The sky has long been read, and the climate crisis has renewed the need to read it. Today, changes in the atmosphere cannot be grasped simply by looking up at the sky; we encounter them through processes of observation, recording, classification, and interpretation. Yet the processes through which such readings are produced often recede behind their results. This study addresses this problem through the concept of environmental legibility, which refers to the process by which atmospheric change becomes perceptible and readable. Drawing on Derrida’s grammatology and on Ingold’s and Böhme’s accounts of atmospheric perception, the study distinguishes two dimensions of inscription. Material-atmospheric inscription refers to physical changes that register as perceptible or measurable differences. Discursive-technical inscription refers to the human and technical practices through which such differences are recorded, classified, and calculated. The legibility of the sky emerges through the interplay of these two dimensions. This interplay is examined through Susan Schuppli’s Can the Sun Lie? (2014) and Trevor Paglen’s CLOUD series (2019). Schuppli foregrounds how atmospheric difference becomes evidence, while Paglen makes visible how visual differences are selected as algorithmic features. Together, the two works show how the sky becomes legible and how the conditions of its reading recede behind the result.