(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
In 1958, Keeling 
began measuring atmospheric CO2 concentrations from ... scientific linkages 
between fossil fuel combustion and global climate change due to the greenhouse 
effect.