Charles David ("Dave") Keeling, the first person to devote his life to measuring a key parameter of climate change. Upper: in 1961, photographed from R/V ARGO at dock in Wellington, New Zealand before departing on an expedition. Lower: In 1990s.

upper: Scripps Archives, UCSD (photo by Harmon Craig)
lower: American Geophysical Union, courtesy AIP Emilio Segrè Visual Archives.