Xu et al. (2012)
Also: Xu et al. 2012
Carbon isotopic evidence for the associations of decreasing atmospheric CO2 level with the Frasnian-Famennian mass extinction
Xu, B., Z. Gu, C. Wang, Q. Hao, J. Han, Q. Liu, L. Wang, and Y. Lu (2012), Carbon isotopic evidence for the associations of decreasing atmospheric CO2 level with the Frasnian-Famennian mass extinction, J. Geophys. Res., 117, G01032. Link to PDF
doi:10.1029/2011JG001847
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.