Carbon Dioxide and Climate: A Scientific Assessment.
Charney, Jule G., Akio Arakawa, D. James Baker, Bert Bolin, Robert E. Dickinson, Richard M. Goody, Cecil E. Leith, Henry M. Stommel, and Carl I. Wunch, 1979. Carbon Dioxide and Climate: A Scientific Assessment. Washington, DC, National Academy of Sciences, 22 pp.
Essay about this article
Jule Gregory Charney (1917-1981), a leader in numerical weather prediction and one of the dominant figures in the emergence of atmospheric science, chaired a distinguished ad hoc study group on carbon dioxide and climate for the National Academy of Sciences. The task, to undertake an independent critical assessment of the emerging scientific consensus that increasing carbon dioxide will lead to a warmer Earth with a different distribution of climatic regimes, was undertaken at the request of the President’s Office of Science and Technology Policy. The focus of the study group was the following question: “If it were indeed certain that atmospheric carbon dioxide would increase on a known schedule, how well could we project the climatic consequences?”
The experiments of John Tyndall in the nineteenth century had demonstrated the significant role carbon dioxide plays in the heat budget of the atmosphere. The careful measurements of Charles D. Keeling since 1958 had provided incontrovertible evidence that atmospheric concentrations of carbon dioxide are steadily increasing. Carbon-14 abundance studies had linked this increase to humanity’s use of fossil fuels and exploitation of the land, while spectroscopic studies had indicated that carbon dioxide plays a significant role in the heat budget of the atmosphere. Thus it was reasonable to suppose that continued increases in carbon dioxide would warm the climate, a result in agreement with the results of climate modelers.
The study group examined general circulation models being developed at NOAA’s Geophysical Fluid Dynamics Laboratory and NASA’s Goddard Institute for Space Studies and accessed each model’s ability to emulate the processes of the actual atmosphere and climate system. All the current models, although quite sophisticated in their own right, were lacking in comprehensive routines to calculate the effects of cloud feedbacks and ocean-atmosphere interactions.
Clouds have the potential to act as either positive or negative temperature feedback mechanisms. They are efficient at both scattering solar radiation and absorbing and emitting long wave radiation. Upper level clouds were assumed to have a net warming effect and lower clouds a net cooling effect on the climate. The amount and type of cloud cover is dependent on other complex feedback mechanisms which themselves may be dependent on the presence of clouds (see Cess, et al., 1989). Ocean-atmosphere interactions presented another set of issues. The group concluded it is possible that the ocean, with its ability to absorb vast amounts of heat, “acts as a ponderous flywheel of the global climate system,” and may delay noticeable temperature increases by several decades.
Based on a review of the results of state-of-the-art computer models, scientific theory, and the results of field measurements, the group estimated that Earth’s average temperature was likely to increase by 1.5 to 4.5 oC by the middle of the twenty-first century and that weather patterns will significantly change as a result of global warming. The ability to evaluate the degree to which the nation’s socio-economic standing would be immediately affected by climate change, however, was deemed to lie beyond the expertise of the group.
a. Discuss how an emerging scientific consensus can be used in policy deliberations among non-scientists, with specific reference to the carbon dioxide theory of climate change.
b. Compare the results of this 1979 study with what is currently known about climate sensitivity to doubling carbon dioxide concentrations and also with regard to societal implications.
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