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his year marks the 50th anniversary of the start of the Mauna Loa CO 2 record, the longest continuous record of CO 2 in the atmosphere. Initiated by my father, Charles D. Keeling of the Scripps Institution of Oceanography, the record pro-vided the first compelling evidence that the concentration of CO 2 in the atmosphere was rising. It has become an icon of the human imprint on the planet and a continuing resource for the study of the changing global carbon cycle. The Mauna Loa story (1) pro-vides a valuable lesson on the importance of continuous Earth observations in a time of accelerating global change. At the outset, the decision to place the instrument at Mauna Loa was a gamble. Existing measurements suggested that atmo-spheric CO 2 concentrations varied widely depending on the place and time. Given this variability, could a meaningful record be recov-ered from an instrument parked in one loca-tion? Among the skeptics was Roger Revelle, then director of the Scripps Institution of Oceanography. Revelle would eventually become one of the record’s strongest champi-ons. Initially, however, he urged that priority be given to a one-time survey of CO 2 variability using ships and airplanes. Such a survey could be repeated a decade or so later to look for long-term changes. My father was armed with evidence from his postdoctoral research that the CO 2 concen-tration in the remote atmosphere was a lot less variable than previously believed (2). He also had a strong ally in Harry Wexler of the U.S. Weather Bureau, who envisioned a central role for the newly established Mauna Loa Observatory (see the photo) in the major field program planned for the International Geophysical Year of 1957–1958. The value of the Mauna Loa data soon was apparent (3). By the second year, a regular seasonal cycle was evident, reflecting the “breathing ” of land plants in the Northern Hemisphere. Together with a more limite