Manabe & Wetherald (1967)
Also: Manabe & Wetherald 1967
Thermal equilibrium of the atmosphere with a given distribution of relative humidity
Manabe, S., & Wetherald, R.T. (1967). Thermal equilibrium of the atmosphere with a given distribution of relative humidity. Journal of Atmospheric Sciences, 24, 24159. Link to PDF
References
All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.