Etheridge et al. (1996)
Also: Etheridge et al. 1996
Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn
Etheridge, D. M., Steele, L. P., Langenfelds, R. L., Francey, R. J., Barnola, J. M., & Morgan, V. I. (1996). Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn. Journal of Geophysical Research: Atmospheres, 101(D2), 4115-4128. Link to paper.
DOI: 10.1029/95JD03410
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.