Jin, H.J., Chang, X.L. and Wang, S.L. 2007. Evolution of permafrost on the Qinghai-Xizang (Tibet) Plateau since the end of the late Pleistocene. Journal of Geophysical Research 112: 10.1029/2006JF000521.
The authors describe "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 they report that during "the warm period in the later Holocene (1000 to 500 years BP)," 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."