Lamb 1965
Also: Lamb (1965)
The early medieval warm epoch and its sequel
Lamb, H.H. (1965). The early medieval warm epoch and its sequel. Palaeogeography, Palaeoclimatology, Palaeoecology. 1. 13-37. Link to article.
https://doi.org/10.1016/0031-0182(65)90004-0
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.