Through his worldwide industrial civilization, Man is unwittingly conducting a vast geophysical experiment. Within a few generations he is burning the fossil fuels that slowly accumulated in the earth over the past 500 million years. The CO2 produced by this combustion is being injected into the atmosphere; about half of it remains there. The estimated recoverable reserves of fossil fuels are sufficient to produce nearly a 200% increase in the carbon dioxide content of the atmosphere.
...The climatic changes that may be produced by the increased CO2 content could be deleterious from the point of view of human beings.
From
Restoring the Quality of Our Environment: Report of the Environmental Pollution Panel, President's Advisory Committee, November
1965, Appendix Y4: Atmospheric Carbon Dioxide (
PDF). The authors credit T.C. Chamberlain and Svante Arrhenius with the first speculation about the phenomenon, in 1899 and 1903, respectively.