What was done
The authors compared Ge et al.'s (2003) reconstructed winter half-year temperature anomalies in the central region of eastern China (25-40°N, east of 105°E) for the last 1000 years with simulated anomalies of the same parameter, which they obtained from the ECHO-G global atmosphere-ocean coupled climate model that was driven by time-varying external forcings, including solar radiation, volcanic eruptions, and greenhouse gas concentrations (CO2 and CH4) for the same time period.

What was learned
Liu et al. report that "the Medieval Warm Period (MWP) during 1000-1300 A.D., the Little Ice Age (LIA) during 1300-1850 A.D. and the modern warming period after 1900 A.D. are all recognizable from both the simulated and reconstructed temperatures." They also report that the anomalies associated with the LIA and the modern warming simulated by the model are "in good consistency" with their reconstructed counterparts. However, they note that "in the earlier MWP, significant discrepancies exist between the simulation and the reconstruction." More specifically, they say that "the simulated temperature anomaly in the 20th century is higher than that of the Medieval Warm Period, while the reconstructed temperature in the 20th century is lower."

What it means
The seven scientists say the two different results "provide two different interpretations regarding the amplitude of recent global warming," noting that "one states that the 20th century warming has exceeded the normal range of the climate change, and it will result in catastrophic impact on human beings if warming continues," while the other suggests that "the current climate change has not yet exceeded the range of natural climate change in the past millennium." And that is why we continue to post the results of one new MWP study every single week on our website. As the real-world evidence for a warmer-than-present Medieval Warm Period continues to accumulate, it is getting harder and harder to believe the climate-alarmist claim that current temperatures are unnaturally high due to anthropogenic CO2 emissions, because the atmospheric CO2 concentration during the Medieval Warm Period was fully 100 ppm less than it is today, while temperatures then were either equivalent to, or (more likely) even higher than, they are currently.

Reference
Ge, Q., Zheng, J., Fang, X., Man, Z., Zhang, X., Zhang, P. and Wang, W.-C. 2003. Winter half-year temperature reconstruction for the middle and lower reaches of the Yellow River and Yangtze River, China, during the past 2000 years. The Holocene 13: 933-940.