(Sarah of the Clue Crew reports from a beach UC San Diego's Scripps Institution of Oceanography.)  In 1958, Scripps scientist Charles Keeling began using flasks to measure this gas in the atmosphere; the "Keeling curve" is a symbol of climate change
It is based on continuous 
measurements taken at the Mauna Loa Observatory in Hawaii that began under 
the supervision of Charles David Keeling.