A growing library of peer reviewed studies provides mounting empirical evidence that the medieval warming was also experienced in the Southern Hemisphere. The latest study that discredits the 'hockey stick' bogosity comes from scientists analyzing past climate conditions on New Caledonia.
Wirrmann et al. confirmed that the peak mangrove growth was during the 950 to 1250 AD period, which would conform to the approximate Medieval period in the Northern Hemisphere. The tropical mangrove plant prospers in warmer climates.
"Based on their multi-proxy approach to climate evaluation, the authors determined that between ca. 2640 and 2000 cal yr BP, conditions were "drier and cooler," while subsequent observations linked wetter with warmer. More specifically, they report that "between ca. 1250-500 cal yr BP the higher % of Rhizophoraceae and their peak around ca. 1080-750 cal yr BP underscore a mangrove belt development along the coastline." And they state that this episode must be related to a wetter period and "may be related to a more global phenomenon such as the MWP in the Northern Hemisphere." [Denis Wirrmanna, Anne-Marie Sémaha, Jean-Pierre Debenayb, Magali Chacornac-Raultc 2011: Quaternary Research]