Read here. The research keeps being conducted, providing further scientific evidence that the Medieval Warming was considerably warmer that the current period warming of the late 20th and early 21st century. The irrefutable climate data continues to mount regarding the extreme variation in historical temperatures, as this chart indicates. (click on image to enlarge)
"Kobashi et al. (2010) constructed a history of the last thousand years of central Greenland surface air temperature, based on values of isotopic ratios of nitrogen and argon...from air bubbles trapped in the GISP2 ice core that had been extracted from central Greenland...results reveal that the latter part of the Medieval Warm Period was approximately 1.67°C greater than the temperature of the last decades of the 20th century, which climate alarmists claim to have been the warmest of the past millennium."