Past climate variability in the Last Millennium

Abstract

We review our knowledge of the climate variability in southern Africa over the past millennium, based on information provided by proxy data and by climate simulations. Since proxy data almost exclusively record past temperature and/or precipitation, the review is focused on those two variables. Proxy data identify three thermal phases in the region: a medieval warm period around year 1000 CE (common era), a Little Ice Age until about the eighteenth century, and a clear warming phase since that temperature minimum until the present period. Variations of precipitation are different in the summer-rainfall and winter-rainfall regions. In the former, precipitation tends to accompany the temperature, with warm/humid and cold/dry phases. In the winter-rainfall zone, the variations are opposite to temperature. Thus, past precipitation variations display a see-saw pattern between the summer- and winter-rainfall zones. However, climate simulations do not display these three different hydroclimatic periods. Instead, the simulations show a clearly warm twentieth century and punctuated cooling due to volcanic eruptions, with otherwise little variations during the pre-industrial period. Also, the simulations do not indicate an anticorrelation between precipitation in the summer- and winter-rainfall zones. Possible reasons for these discrepancies are discussed.