Read here. The IPCC and Climategate scientists, such as Michael Mann, attempted to mislead the public and policymakers with claims that the Medieval Warming Period was an insignificant climate event only affecting the northern European areas. However, the empirical evidence continues to grow that the Southern Hemisphere experienced a global medieval warming climate also.
Analyzing sediment cores from the Merín Lagoon Basin, in the region of the ancient Uruguay 'Los Ajos' mound builders, it was determined from opal phytoliths that Uruguay's climate of 750 AD to 1350 AD was warmer and wetter than those of its current modern climate.
"Focusing on coastal lagoons within the Merin Lagoon Basin, which is located between 31-34°S and 52-54°W in the easternmost part of the South American plains, and working with phytoliths found within various sediment cores which they used to create a temperature index indicative of relative warmth, Bracco et al. discovered a period of time straddling the division of the last two millennia (AD 750-1350) that they identified as having "warmer and wetter conditions than those of the present."" [Roberto Bracco, Laura del Puerto, Hugo Inda, Daniel Panario, Carola Castiñeira, Felipe García-Rodríguez 2011: Quaternary International]
Conclusion: Medieval global warming was a significant climate phenomenon that empirically prevailed across the world and not just limited to the northern European/Atlantic region as fabricated by the IPCC.