Climate change. Climate in Medieval time

Many papers have referred to a "Medieval Warm Period." But how well defined is climate in this period, and was it as warm as or warmer than it is today? In their Perspective, Bradley et al. review the evidence and conclude that although the High Medieval (1100 to 1200 A.D.) was warmer than subsequent centuries, it was not warmer than the late 20th century. Moreover, the warmest Medieval temperatures were not synchronous around the globe. Large changes in precipitation patterns are a particular characteristic of "High Medieval" time. The underlying mechanisms for such changes must be elucidated further to inform the ongoing debate on natural climate variability and anthropogenic climate change.