What was done
The authors report the results of their study of plant cellulose ð¹⁸O variations in cores retrieved from peat deposits west of Hongyuan County at the northeastern edge of the Qinghai-Tibetan Plateau (32° 46'N, 102° 30'E) in China.

What was learned
Following the demise of what has been called the Roman Warm Period, the authors note the existence of three consistently cold events that were centered at approximately 500, 700 and 900 AD, during what is sometimes referred to as the Dark Ages Cold Period.  Then, from 1100-1300 AD, they report "the ð¹⁸O of Hongyuan peat cellulose increased, consistent with that of Jinchuan peat cellulose and corresponding to the 'Medieval Warm Period'."  Finally, they note that "the periods 1370-1400 AD, 1550-1610 AD, [and] 1780-1880 AD recorded three cold events, corresponding to the 'Little Ice Age'."

Regarding the origins of these climatic fluctuations, power spectrum analyses of their data revealed periodicities of 79, 88 and 123-127 years, "suggesting," in the words of the authors, "that the main driving force of Hongyuan climate change is from solar activities."

What it means
As more and more scientists dig into all parts of the planet to study its climatic history, they unearth more and more evidence for the global reality of the [likely] solar-forced millennial-scale climatic oscillation that has alternately brought us long intervals of relative warmth and coolness, such as the Roman Warm Period, the Dark Ages Cold Period, the Medieval Warm Period, the Little Ice Age and, most recently, the Modern Warm Period.