Ralph Keeling is professor of geochemistry in the Geosciences Research Division of Scripps Institution of Oceanography, University of California, San Diego. His research focuses on atmospheric composition, the carbon cycle, and climate change. He is considered a leading investigator of the global oxygen cycle for his precise measurements and analysis techniques. Keeling developed his method for measuring atmospheric oxygen levels utilizing interferometry techniques in the laboratory. He began pioneering measurements of changes in atmospheric oxygen levels from air samples collected at stations around the world. The measurements continue at nine sampling stations, extending from Ellesmere Island in northern Canada over the equator to two Antarctic stations.