[Illustrations, footnotes and references available in PDF version]
Was there a Medieval Warm Period anywhere in addition to the area surrounding the North Atlantic Ocean, where its occurrence is uncontested? This question is of utmost importance to the ongoing global warming debate, since if there was, and if the locations where it occurred were as warm then as they are currently, there is no need to consider the temperature increase of the past century as anything other than the natural progression of the persistent millennial-scale oscillation of climate that regularly brings the earth several-hundred-year periods of modestly higher and lower temperatures that are totally independent of variations in atmospheric CO2 concentration. Hence, this question is here considered as it applies to South America, a region far removed from where the existence of the Medieval Warm Period was first recognized.
ST data indicate that the current level of warmth in that part of the world still has a long way to go before equaling the warmth experienced there a thousand and more years ago, which suggests that the region's current level of warmth is neither unprecedented nor unnatural -and therefore need not be CO2-induced - as is also the case for most of the rest of the planet.
This finding of Neukom et al. goes a long ways towards demonstrating that: (1) the Medieval Warm Period was a global phenomenon that was comprised of even warmer intervals than the warmest portion of the Current Warm Period, and that (2) the greater warmth of the Medieval Warm Period occurred when there was far less CO2 in the air than there is nowadays, which facts clearly demonstrate that the planet's current - but not unprecedented - degree of warmth need not have been CO2-induced.