Read here. In the broad realm of empirical evidence for Medieval Warming, there is one unique indicator that does not require a Phd to appreciate and understand - that would be tree lines. In general, if the climate is warmer, the tree line will move farther north and/or to higher elevations. As scientists discovered in the Ural Mountains, the modern tree line is at a much lower elevation than the Medieval tree line.
"Most importantly, Mazepa reports that "a large number of well-preserved tree remains can be found up to 60-80 meters above the current tree line, some dating to as early as a maximum [our italics] of 1300 years ago," and that "the earliest distinct maximum in stand density [our italics] occurred in the 11th to 13th centuries, coincident with Medieval climatic warming.".....Noting that "dead trees located above the current tree-line ecotone provide evidence of the dynamic behavior in the location of the tree line in the recent past (Shiyatov, 1993, 2003)," Mazepa reports that "previous studies have concluded that increases in tree-line elevation, and associated increases in tree abundance within the transient tree-line ecotone, are associated with extended warm periods"
Additional climate history postings.