Read here. Map source here. Scientists, using sediment cores, determine that all the historical, major climate changes have impacted the Southern Hemisphere at approximately the same times as impacting the Northern Hemisphere.
"Signy Island [in Southern Ocean, near Antarctica] is seen to have experienced the relative warmth of the last vestiges of the Roman Warm Period...Then comes the Dark Ages Cold period...after which the Medieval Warm Period appears at the same point in time and persists for the same length of time that it does in the vicinity of Ireland, whereupon the Little Ice Age sets in just as it does in the Northern Hemisphere. Finally, there is an indication of late 20th century warming, but with still a long way to go before conditions comparable to those of the Medieval Warm Period are achieved..... it demonstrates that the global warming of the past century, which led to the demise of the Little Ice Age, is but the most recent phase of a natural climatic oscillation that is totally unrelated to the increase in the air's CO2 content that just happened to coincide with its occurrence."
Additional climate history postings