Lamb, H.F., Leng, M.J., Telford, R.J., Ayenew, T. and Umer, M. 2007. Oxygen and carbon isotope composition of authigenic carbonate from an Ethiopian lake: a climate record of the last 2000 years. The Holocene 17: 517-526.
Lamb et al. developed a 2000-year history of effective precipitation based upon oxygen and carbon isotope and pollen stratigraphy data derived from a sediment core taken from Lake Hayq (11°21'N, 39°43'E) on the eastern margin of the north-central highlands in South Wollo, Ethiopia. This record revealed, in their words, that a "similar, but slightly moister climate than today, with high interdecadal variability, prevailed from AD 800 to AD 1200, equivalent to the European 'Mediaeval Warm Period'," and that "a period of high effective precipitation followed, from AD 1200 to AD 1700, during the 'Little Ice Age'."