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Millennial-Scale Climate Variability in Southern Africa
Reference
Holmgren, K., Lee-Thorp, J.A., Cooper, G.R.J., Lundblad, K., Partridge, T.C., Scott, L., Sithaldeen, R., Talma, A.S. and Tyson, P.D. 2003. Persistent millennial-scale climatic variability over the past 25,000 years in Southern Africa. Quaternary Science Reviews 22: 2311-2326.

What was done
The authors developed a 25,000-year temperature history from a stalagmite retrieved from Cold Air Cave (241'S, 2911'E) in the Makapansgat Valley of South Africa that was based on 18O and 13C measurements dated by 14C and high-precision thermal ionization mass spectrometry using the 230Th/234U method.

What was learned
In the words of the authors [with our interspersed notes], "cooling is evident from ~6 to 2.5ka [thousand years before present, during the long interval of coolness that preceded the Roman Warm Period], followed by warming between 1.5 and 2.5 ka [the Roman Warm Period] and briefly at ~AD 1200 [the Medieval Warm Period, which followed the Dark Ages Cold Period]," after which "maximum Holocene cooling occurred at AD 1700 [the depth of the Little Ice Age]." They also note that "the Little Ice Age covered the four centuries between AD 1500 and 1800 and at its maximum at AD 1700 represents the most pronounced negative 18O deviation in the entire record."

What it means
This new temperature record from far below the equator (24S) reveals the existence of all the major millennial-scale oscillations of climate that are evident in data collected from regions surrounding the North Atlantic Ocean. Hence, it attests to the global extent of these significant intervals of relative warmth and coolness; and it suggests that, after the coldest such period of the entire Holocene, it was only to be expected there would be a significant increase in mean global air temperature when the next scheduled warming took place [for evidence of the great regularity and, hence, "scheduling" of these events, see Rahmstorf (2003)]. Once these facts are appreciated, it is easy to see there is nothing unusual about either the extent or rate of rise of earth's temperature over the past century or so.

Reference
Rahmstorf, S. 2003. Timing of abrupt climate change: A precise clock. Geophysical Research Letters 30: 10.1029/2003GL017115.


Reviewed 31 December 2003