A rising level of CO2 in the atmosphere was first demonstrated in 1960 in Antarctica, visible after only two years of measurements. Upper: Keeling's graph. Lower: the Little America Navy base shortly after it was established in 1956.

C. D. Keeling, Tellus 12, (1960), p. 200, reproduced by permission.

Little America. Watercolor & pencil sketch by Robert Charles Haun, January 1956.
Courtesy Dept. of the Navy, Naval Historical Center, 88-192-BF