Background
The total area of permafrost on the Qinghai-Tibet Plateau, according to the authors, is "estimated to be between 1.3 and 1.6 million km², making it the largest expanse of elevational permafrost in the world," and they write that it "was formed during the last two major glaciations, and was not completely thawed during the intervening warmer periods."

What was done
Jin et al. discuss "the evolutionary history of permafrost in the central and eastern Qinghai-Tibetan Plateau since the end of the late Pleistocene, using relict permafrost and periglacial phenomena along the Qinghai-Tibet Highway from Gomud to Lhasa, the Qinghai-Kang (western Sichuan) Highway from Xi'ning to Yusu, adjacent areas, and the Xinjiang-Tibet Highway from Yecheng to Lhasa." Among their many findings, we focus our attention on their descriptions of permafrost and deduced environmental conditions during "the Megathermal period in the middle Holocene (~8500-7000 to ~4000-3000 years BP)," as well as "the warm period in the later Holocene (1000 to 500 years BP)," wherein they compare environmental and permafrost characteristics during those periods of elevated warmth with those of the present.

What was learned
The three researchers from the Chinese Academy of Sciences report that during the Megathermal period of the middle Holocene, "the total areas of permafrost then were about 40-50% of those at present," while "mean annual air temperatures were ~2-3°C higher." Likewise, they report that during the warm period of the late Holocene, "the retreating of permafrost resulted in a total permafrost area of ~20-30% less than at present," while mean annual air temperatures were "1.5-2.0°C warmer than at present."

What it means
Clearly, mean annual air temperatures over the vast expanse of the Qinghai-Tibet Plateau during both the Megathermal of the middle Holocene and the Medieval Warm Period of the late Holocene were both significantly warmer than those of the present, providing ever more evidence for the hollowness of the climate-alarmist claim that the Medieval Warm Period was but a local phenomenon confined to high-latitude lands surrounding the North Atlantic Ocean, as well as the claim of Hansen et al. (2006), who in reference to a single point of the earth's surface in the Western Equatorial Pacific stated that "this critical ocean region, and probably the planet as a whole [our italics], is approximately as warm now as at the Holocene maximum and within ~1°C of the maximum temperature of the past million years [our italics]."

Reference
Hansen, J., Sato, M., Ruedy, R., Lo, K., Lea, D.W. and Medina-Elizade, M. 2006. Global temperature change. Proceedings of the National Academy of Sciences USA 103: 14,288-14,293.