The "Keeling curve" of CO2 measured at Mauna Loa, Hawaii, as seen in 1971. (The annual cycle reflects uptake and release of the gas from plants and soil in the northern hemisphere.) The full curve into the 21st century is shown here. A gap in 1964 was due to problems that could have been avoided with better funding.

From Inadvertent Climate Modification. Report of Conference, Study of Man's Impact on Climate (SMIC), Stockholm, edited by Carroll L.Wilson and William H. Matthews , p. 234, copyright MIT Press, 1971.