Climate Research From Briffa, Esper, Jones, Moberg & Mann All Confirm The Extreme Medieval Warming
During U.S. Senate testimony (2005), evidence was presented that revealed multiple studies supporting a consensus that the Medieval Period experienced extreme warming that matches or exceeds any modern, post-1970's warming. The multi-graph below represents the research from major climate researchers that was presented at the Senate testimony. It's of interest to note that none of these scientists are considered global warming "skeptics." (Source of multi-graph from 2005 testimony.)
Besides these studies, hundreds of scientists have conducted research that more often than not, confirm that Medieval Warming was unprecedented. For a quick review of historical climate charts that show this, go here. In addition, C3 has compiled a page that includes climate-history postings, with and without charts. (click on image to enlarge)
"According to the six scientists, we understand, for the most part, the shape of long-term climate fluctuations better than their amplitudes. For instance, nearly all 1000-year temperaturereconstructions capture the major climatic episodes of the Medieval Warm Period, Little Ice Age and Current Warm Period; but for various reasons they exhibit differences in the degree of climatic warming or cooling experienced in the transitions between them, which for decadal means may amount to as much as 0.4 to 1.0°C...knowledge of the correct amplitude of the major climatic episodes of the past millennium is "critical for predicting future trends." Why? Because if it can be shown that the amplitudes of the major historical climate episodes were as large as, or even greater than, that of 20th-century global warming, there would be a "redistribution of weight towards the role of natural factors in forcing temperature changes, thereby relatively devaluing the impact of anthropogenic emissions and affecting future predicted scenarios.""