Barnosky et al. (2011)
Also: Barnosky et al. 2011
Has the Earth/'s sixth mass extinction already arrived?
Barnosky, A. D., Matzke, N., Tomiya, S., Wogan, G. O., Swartz, B., Quental, T. B., ... & Ferrer, E. A. (2011). Has the Earth's sixth mass extinction already arrived?. Nature 471(7336), 51-57. Link to paper
doi: 10.1038/nature09678
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.