Breecker et al. (2009)
Also: Breecker et al. 2009
Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for AD2100
Breecker, D.O., Sharp, Z.D., & McFadden, L.D. (2009). Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for AD2100. PNAS, 107(2), 576-580. Link to article
doi: 10.1073/pnas.0902323106
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.